gecko-dev/xpcom/base/nsCycleCollector.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim: set ts=8 sts=4 et sw=4 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//
// This file implements a garbage-cycle collector based on the paper
//
//   Concurrent Cycle Collection in Reference Counted Systems
//   Bacon & Rajan (2001), ECOOP 2001 / Springer LNCS vol 2072
//
// We are not using the concurrent or acyclic cases of that paper; so
// the green, red and orange colors are not used.
//
// The collector is based on tracking pointers of four colors:
//
// Black nodes are definitely live. If we ever determine a node is
// black, it's ok to forget about, drop from our records.
//
// White nodes are definitely garbage cycles. Once we finish with our
// scanning, we unlink all the white nodes and expect that by
// unlinking them they will self-destruct (since a garbage cycle is
// only keeping itself alive with internal links, by definition).
//
// Snow-white is an addition to the original algorithm. Snow-white object
// has reference count zero and is just waiting for deletion.
//
// Grey nodes are being scanned. Nodes that turn grey will turn
// either black if we determine that they're live, or white if we
// determine that they're a garbage cycle. After the main collection
// algorithm there should be no grey nodes.
//
// Purple nodes are *candidates* for being scanned. They are nodes we
// haven't begun scanning yet because they're not old enough, or we're
// still partway through the algorithm.
//
// XPCOM objects participating in garbage-cycle collection are obliged
// to inform us when they ought to turn purple; that is, when their
// refcount transitions from N+1 -> N, for nonzero N. Furthermore we
// require that *after* an XPCOM object has informed us of turning
// purple, they will tell us when they either transition back to being
// black (incremented refcount) or are ultimately deleted.

// Incremental cycle collection
//
// Beyond the simple state machine required to implement incremental
// collection, the CC needs to be able to compensate for things the browser
// is doing during the collection. There are two kinds of problems. For each
// of these, there are two cases to deal with: purple-buffered C++ objects
// and JS objects.

// The first problem is that an object in the CC's graph can become garbage.
// This is bad because the CC touches the objects in its graph at every
// stage of its operation.
//
// All cycle collected C++ objects that die during a cycle collection
// will end up actually getting deleted by the SnowWhiteKiller. Before
// the SWK deletes an object, it checks if an ICC is running, and if so,
// if the object is in the graph. If it is, the CC clears mPointer and
// mParticipant so it does not point to the raw object any more. Because
// objects could die any time the CC returns to the mutator, any time the CC
// accesses a PtrInfo it must perform a null check on mParticipant to
// ensure the object has not gone away.
//
// JS objects don't always run finalizers, so the CC can't remove them from
// the graph when they die. Fortunately, JS objects can only die during a GC,
// so if a GC is begun during an ICC, the browser synchronously finishes off
// the ICC, which clears the entire CC graph. If the GC and CC are scheduled
// properly, this should be rare.
//
// The second problem is that objects in the graph can be changed, say by
// being addrefed or released, or by having a field updated, after the object
// has been added to the graph. This will be addressed in bug 937818.


// Safety
//
// An XPCOM object is either scan-safe or scan-unsafe, purple-safe or
// purple-unsafe.
//
// An nsISupports object is scan-safe if:
//
//  - It can be QI'ed to |nsXPCOMCycleCollectionParticipant|, though
//    this operation loses ISupports identity (like nsIClassInfo).
//  - Additionally, the operation |traverse| on the resulting
//    nsXPCOMCycleCollectionParticipant does not cause *any* refcount
//    adjustment to occur (no AddRef / Release calls).
//
// A non-nsISupports ("native") object is scan-safe by explicitly
// providing its nsCycleCollectionParticipant.
//
// An object is purple-safe if it satisfies the following properties:
//
//  - The object is scan-safe.
//
// When we receive a pointer |ptr| via
// |nsCycleCollector::suspect(ptr)|, we assume it is purple-safe. We
// can check the scan-safety, but have no way to ensure the
// purple-safety; objects must obey, or else the entire system falls
// apart. Don't involve an object in this scheme if you can't
// guarantee its purple-safety. The easiest way to ensure that an
// object is purple-safe is to use nsCycleCollectingAutoRefCnt.
//
// When we have a scannable set of purple nodes ready, we begin
// our walks. During the walks, the nodes we |traverse| should only
// feed us more scan-safe nodes, and should not adjust the refcounts
// of those nodes.
//
// We do not |AddRef| or |Release| any objects during scanning. We
// rely on the purple-safety of the roots that call |suspect| to
// hold, such that we will clear the pointer from the purple buffer
// entry to the object before it is destroyed. The pointers that are
// merely scan-safe we hold only for the duration of scanning, and
// there should be no objects released from the scan-safe set during
// the scan.
//
// We *do* call |Root| and |Unroot| on every white object, on
// either side of the calls to |Unlink|. This keeps the set of white
// objects alive during the unlinking.
//

#if !defined(__MINGW32__)
#ifdef WIN32
#include <crtdbg.h>
#include <errno.h>
#endif
#endif

#include "base/process_util.h"

#include "mozilla/ArrayUtils.h"
#include "mozilla/AutoRestore.h"
#include "mozilla/CycleCollectedJSRuntime.h"
/* This must occur *after* base/process_util.h to avoid typedefs conflicts. */
#include "mozilla/MemoryReporting.h"
#include "mozilla/LinkedList.h"

#include "nsCycleCollectionParticipant.h"
#include "nsCycleCollectionNoteRootCallback.h"
#include "nsDeque.h"
#include "nsCycleCollector.h"
#include "nsThreadUtils.h"
#include "prenv.h"
#include "nsPrintfCString.h"
#include "nsTArray.h"
#include "nsIConsoleService.h"
#include "mozilla/Attributes.h"
#include "nsICycleCollectorListener.h"
#include "nsIMemoryReporter.h"
#include "nsIFile.h"
#include "nsMemoryInfoDumper.h"
#include "xpcpublic.h"
#include "GeckoProfiler.h"
#include "js/SliceBudget.h"
#include <stdint.h>
#include <stdio.h>

#include "mozilla/Likely.h"
#include "mozilla/PoisonIOInterposer.h"
#include "mozilla/Telemetry.h"
#include "mozilla/ThreadLocal.h"

using namespace mozilla;

//#define COLLECT_TIME_DEBUG

// Enable assertions that are useful for diagnosing errors in graph construction.
//#define DEBUG_CC_GRAPH

#define DEFAULT_SHUTDOWN_COLLECTIONS 5

// One to do the freeing, then another to detect there is no more work to do.
#define NORMAL_SHUTDOWN_COLLECTIONS 2

// Cycle collector environment variables
//
// XPCOM_CC_LOG_ALL: If defined, always log cycle collector heaps.
//
// XPCOM_CC_LOG_SHUTDOWN: If defined, log cycle collector heaps at shutdown.
//
// XPCOM_CC_ALL_TRACES_AT_SHUTDOWN: If defined, any cycle collector
// logging done at shutdown will be WantAllTraces, which disables
// various cycle collector optimizations to give a fuller picture of
// the heap.
//
// XPCOM_CC_RUN_DURING_SHUTDOWN: In non-DEBUG or builds, if this is set,
// run cycle collections at shutdown.
//
// MOZ_CC_LOG_DIRECTORY: The directory in which logs are placed (such as
// logs from XPCOM_CC_LOG_ALL and XPCOM_CC_LOG_SHUTDOWN, or other uses
// of nsICycleCollectorListener)

MOZ_NEVER_INLINE void
CC_AbortIfNull(void *ptr)
{
    if (!ptr)
        MOZ_CRASH();
}

// Various parameters of this collector can be tuned using environment
// variables.

struct nsCycleCollectorParams
{
    bool mLogAll;
    bool mLogShutdown;
    bool mAllTracesAtShutdown;

    nsCycleCollectorParams() :
        mLogAll      (PR_GetEnv("XPCOM_CC_LOG_ALL") != nullptr),
        mLogShutdown (PR_GetEnv("XPCOM_CC_LOG_SHUTDOWN") != nullptr),
        mAllTracesAtShutdown (PR_GetEnv("XPCOM_CC_ALL_TRACES_AT_SHUTDOWN") != nullptr)
    {
    }
};

#ifdef COLLECT_TIME_DEBUG
class TimeLog
{
public:
    TimeLog() : mLastCheckpoint(TimeStamp::Now()) {}

    void
    Checkpoint(const char* aEvent)
    {
        TimeStamp now = TimeStamp::Now();
        uint32_t dur = (uint32_t) ((now - mLastCheckpoint).ToMilliseconds());
        if (dur > 0) {
            printf("cc: %s took %dms\n", aEvent, dur);
        }
        mLastCheckpoint = now;
    }

private:
    TimeStamp mLastCheckpoint;
};
#else
class TimeLog
{
public:
    TimeLog() {}
    void Checkpoint(const char* aEvent) {}
};
#endif


////////////////////////////////////////////////////////////////////////
// Base types
////////////////////////////////////////////////////////////////////////

struct PtrInfo;

class EdgePool
{
public:
    // EdgePool allocates arrays of void*, primarily to hold PtrInfo*.
    // However, at the end of a block, the last two pointers are a null
    // and then a void** pointing to the next block.  This allows
    // EdgePool::Iterators to be a single word but still capable of crossing
    // block boundaries.

    EdgePool()
    {
        mSentinelAndBlocks[0].block = nullptr;
        mSentinelAndBlocks[1].block = nullptr;
    }

    ~EdgePool()
    {
        MOZ_ASSERT(!mSentinelAndBlocks[0].block &&
                   !mSentinelAndBlocks[1].block,
                   "Didn't call Clear()?");
    }

    void Clear()
    {
        Block *b = Blocks();
        while (b) {
            Block *next = b->Next();
            delete b;
            b = next;
        }

        mSentinelAndBlocks[0].block = nullptr;
        mSentinelAndBlocks[1].block = nullptr;
    }

#ifdef DEBUG
    bool IsEmpty()
    {
        return !mSentinelAndBlocks[0].block &&
               !mSentinelAndBlocks[1].block;
    }
#endif

private:
    struct Block;
    union PtrInfoOrBlock {
        // Use a union to avoid reinterpret_cast and the ensuing
        // potential aliasing bugs.
        PtrInfo *ptrInfo;
        Block *block;
    };
    struct Block {
        enum { BlockSize = 16 * 1024 };

        PtrInfoOrBlock mPointers[BlockSize];
        Block() {
            mPointers[BlockSize - 2].block = nullptr; // sentinel
            mPointers[BlockSize - 1].block = nullptr; // next block pointer
        }
        Block*& Next()          { return mPointers[BlockSize - 1].block; }
        PtrInfoOrBlock* Start() { return &mPointers[0]; }
        PtrInfoOrBlock* End()   { return &mPointers[BlockSize - 2]; }
    };

    // Store the null sentinel so that we can have valid iterators
    // before adding any edges and without adding any blocks.
    PtrInfoOrBlock mSentinelAndBlocks[2];

    Block*& Blocks()       { return mSentinelAndBlocks[1].block; }
    Block*  Blocks() const { return mSentinelAndBlocks[1].block; }

public:
    class Iterator
    {
    public:
        Iterator() : mPointer(nullptr) {}
        Iterator(PtrInfoOrBlock *aPointer) : mPointer(aPointer) {}
        Iterator(const Iterator& aOther) : mPointer(aOther.mPointer) {}

        Iterator& operator++()
        {
            if (mPointer->ptrInfo == nullptr) {
                // Null pointer is a sentinel for link to the next block.
                mPointer = (mPointer + 1)->block->mPointers;
            }
            ++mPointer;
            return *this;
        }

        PtrInfo* operator*() const
        {
            if (mPointer->ptrInfo == nullptr) {
                // Null pointer is a sentinel for link to the next block.
                return (mPointer + 1)->block->mPointers->ptrInfo;
            }
            return mPointer->ptrInfo;
        }
        bool operator==(const Iterator& aOther) const
            { return mPointer == aOther.mPointer; }
        bool operator!=(const Iterator& aOther) const
            { return mPointer != aOther.mPointer; }

#ifdef DEBUG_CC_GRAPH
        bool Initialized() const
        {
            return mPointer != nullptr;
        }
#endif

    private:
        PtrInfoOrBlock *mPointer;
    };

    class Builder;
    friend class Builder;
    class Builder {
    public:
        Builder(EdgePool &aPool)
            : mCurrent(&aPool.mSentinelAndBlocks[0]),
              mBlockEnd(&aPool.mSentinelAndBlocks[0]),
              mNextBlockPtr(&aPool.Blocks())
        {
        }

        Iterator Mark() { return Iterator(mCurrent); }

        void Add(PtrInfo* aEdge) {
            if (mCurrent == mBlockEnd) {
                Block *b = new Block();
                *mNextBlockPtr = b;
                mCurrent = b->Start();
                mBlockEnd = b->End();
                mNextBlockPtr = &b->Next();
            }
            (mCurrent++)->ptrInfo = aEdge;
        }
    private:
        // mBlockEnd points to space for null sentinel
        PtrInfoOrBlock *mCurrent, *mBlockEnd;
        Block **mNextBlockPtr;
    };

    size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
        size_t n = 0;
        Block *b = Blocks();
        while (b) {
            n += aMallocSizeOf(b);
            b = b->Next();
        }
        return n;
    }
};

#ifdef DEBUG_CC_GRAPH
#define CC_GRAPH_ASSERT(b) MOZ_ASSERT(b)
#else
#define CC_GRAPH_ASSERT(b)
#endif

#define CC_TELEMETRY(_name, _value)                                            \
    PR_BEGIN_MACRO                                                             \
    if (NS_IsMainThread()) {                                                   \
      Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR##_name, _value);        \
    } else {                                                                   \
      Telemetry::Accumulate(Telemetry::CYCLE_COLLECTOR_WORKER##_name, _value); \
    }                                                                          \
    PR_END_MACRO

enum NodeColor { black, white, grey };

// This structure should be kept as small as possible; we may expect
// hundreds of thousands of them to be allocated and touched
// repeatedly during each cycle collection.

struct PtrInfo
{
    void *mPointer;
    nsCycleCollectionParticipant *mParticipant;
    uint32_t mColor : 2;
    uint32_t mInternalRefs : 30;
    uint32_t mRefCount;
private:
    EdgePool::Iterator mFirstChild;

public:

    PtrInfo(void *aPointer, nsCycleCollectionParticipant *aParticipant)
        : mPointer(aPointer),
          mParticipant(aParticipant),
          mColor(grey),
          mInternalRefs(0),
          mRefCount(UINT32_MAX - 1),
          mFirstChild()
    {
        // We initialize mRefCount to a large non-zero value so
        // that it doesn't look like a JS object to the cycle collector
        // in the case where the object dies before being traversed.

        MOZ_ASSERT(aParticipant);
    }

    // Allow NodePool::Block's constructor to compile.
    PtrInfo() {
        NS_NOTREACHED("should never be called");
    }

    EdgePool::Iterator FirstChild()
    {
        CC_GRAPH_ASSERT(mFirstChild.Initialized());
        return mFirstChild;
    }

    // this PtrInfo must be part of a NodePool
    EdgePool::Iterator LastChild()
    {
        CC_GRAPH_ASSERT((this + 1)->mFirstChild.Initialized());
        return (this + 1)->mFirstChild;
    }

    void SetFirstChild(EdgePool::Iterator aFirstChild)
    {
        CC_GRAPH_ASSERT(aFirstChild.Initialized());
        mFirstChild = aFirstChild;
    }

    // this PtrInfo must be part of a NodePool
    void SetLastChild(EdgePool::Iterator aLastChild)
    {
        CC_GRAPH_ASSERT(aLastChild.Initialized());
        (this + 1)->mFirstChild = aLastChild;
    }
};

/**
 * A structure designed to be used like a linked list of PtrInfo, except
 * that allocates the PtrInfo 32K-at-a-time.
 */
class NodePool
{
private:
    enum { BlockSize = 8 * 1024 }; // could be int template parameter

    struct Block {
        // We create and destroy Block using NS_Alloc/NS_Free rather
        // than new and delete to avoid calling its constructor and
        // destructor.
        Block()  { NS_NOTREACHED("should never be called"); }
        ~Block() { NS_NOTREACHED("should never be called"); }

        Block* mNext;
        PtrInfo mEntries[BlockSize + 1]; // +1 to store last child of last node
    };

public:
    NodePool()
        : mBlocks(nullptr),
          mLast(nullptr)
    {
    }

    ~NodePool()
    {
        MOZ_ASSERT(!mBlocks, "Didn't call Clear()?");
    }

    void Clear()
    {
        Block *b = mBlocks;
        while (b) {
            Block *n = b->mNext;
            NS_Free(b);
            b = n;
        }

        mBlocks = nullptr;
        mLast = nullptr;
    }

#ifdef DEBUG
    bool IsEmpty()
    {
        return !mBlocks && !mLast;
    }
#endif

    class Builder;
    friend class Builder;
    class Builder {
    public:
        Builder(NodePool& aPool)
            : mNextBlock(&aPool.mBlocks),
              mNext(aPool.mLast),
              mBlockEnd(nullptr)
        {
            MOZ_ASSERT(aPool.mBlocks == nullptr && aPool.mLast == nullptr,
                       "pool not empty");
        }
        PtrInfo *Add(void *aPointer, nsCycleCollectionParticipant *aParticipant)
        {
            if (mNext == mBlockEnd) {
                Block *block = static_cast<Block*>(NS_Alloc(sizeof(Block)));
                *mNextBlock = block;
                mNext = block->mEntries;
                mBlockEnd = block->mEntries + BlockSize;
                block->mNext = nullptr;
                mNextBlock = &block->mNext;
            }
            return new (mNext++) PtrInfo(aPointer, aParticipant);
        }
    private:
        Block **mNextBlock;
        PtrInfo *&mNext;
        PtrInfo *mBlockEnd;
    };

    class Enumerator;
    friend class Enumerator;
    class Enumerator {
    public:
        Enumerator(NodePool& aPool)
            : mFirstBlock(aPool.mBlocks),
              mCurBlock(nullptr),
              mNext(nullptr),
              mBlockEnd(nullptr),
              mLast(aPool.mLast)
        {
        }

        bool IsDone() const
        {
            return mNext == mLast;
        }

        bool AtBlockEnd() const
        {
            return mNext == mBlockEnd;
        }

        PtrInfo* GetNext()
        {
            MOZ_ASSERT(!IsDone(), "calling GetNext when done");
            if (mNext == mBlockEnd) {
                Block *nextBlock = mCurBlock ? mCurBlock->mNext : mFirstBlock;
                mNext = nextBlock->mEntries;
                mBlockEnd = mNext + BlockSize;
                mCurBlock = nextBlock;
            }
            return mNext++;
        }
    private:
        // mFirstBlock is a reference to allow an Enumerator to be constructed
        // for an empty graph.
        Block *&mFirstBlock;
        Block *mCurBlock;
        // mNext is the next value we want to return, unless mNext == mBlockEnd
        // NB: mLast is a reference to allow enumerating while building!
        PtrInfo *mNext, *mBlockEnd, *&mLast;
    };

    size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
        // We don't measure the things pointed to by mEntries[] because those
        // pointers are non-owning.
        size_t n = 0;
        Block *b = mBlocks;
        while (b) {
            n += aMallocSizeOf(b);
            b = b->mNext;
        }
        return n;
    }

private:
    Block *mBlocks;
    PtrInfo *mLast;
};


// Declarations for mPtrToNodeMap.

struct PtrToNodeEntry : public PLDHashEntryHdr
{
    // The key is mNode->mPointer
    PtrInfo *mNode;
};

static bool
PtrToNodeMatchEntry(PLDHashTable *table,
                    const PLDHashEntryHdr *entry,
                    const void *key)
{
    const PtrToNodeEntry *n = static_cast<const PtrToNodeEntry*>(entry);
    return n->mNode->mPointer == key;
}

static PLDHashTableOps PtrNodeOps = {
    PL_DHashAllocTable,
    PL_DHashFreeTable,
    PL_DHashVoidPtrKeyStub,
    PtrToNodeMatchEntry,
    PL_DHashMoveEntryStub,
    PL_DHashClearEntryStub,
    PL_DHashFinalizeStub,
    nullptr
};


struct WeakMapping
{
    // map and key will be null if the corresponding objects are GC marked
    PtrInfo *mMap;
    PtrInfo *mKey;
    PtrInfo *mKeyDelegate;
    PtrInfo *mVal;
};

class GCGraphBuilder;

struct GCGraph
{
    NodePool mNodes;
    EdgePool mEdges;
    nsTArray<WeakMapping> mWeakMaps;
    uint32_t mRootCount;

private:
    PLDHashTable mPtrToNodeMap;

public:
    GCGraph() : mRootCount(0)
    {
        mPtrToNodeMap.ops = nullptr;
    }

    ~GCGraph()
    {
        if (mPtrToNodeMap.ops) {
            PL_DHashTableFinish(&mPtrToNodeMap);
        }
    }

    void Init()
    {
        MOZ_ASSERT(IsEmpty(), "Failed to call GCGraph::Clear");
        if (!PL_DHashTableInit(&mPtrToNodeMap, &PtrNodeOps, nullptr,
                               sizeof(PtrToNodeEntry), 32768)) {
            MOZ_CRASH();
        }
    }

    void Clear()
    {
        mNodes.Clear();
        mEdges.Clear();
        mWeakMaps.Clear();
        mRootCount = 0;
        PL_DHashTableFinish(&mPtrToNodeMap);
        mPtrToNodeMap.ops = nullptr;
    }

#ifdef DEBUG
    bool IsEmpty()
    {
        return mNodes.IsEmpty() && mEdges.IsEmpty() &&
            mWeakMaps.IsEmpty() && mRootCount == 0 &&
            !mPtrToNodeMap.ops;
    }
#endif

    PtrInfo* FindNode(void *aPtr);
    PtrToNodeEntry* AddNodeToMap(void *aPtr);
    void RemoveNodeFromMap(void *aPtr);

    uint32_t MapCount() const
    {
        return mPtrToNodeMap.entryCount;
    }

    void SizeOfExcludingThis(MallocSizeOf aMallocSizeOf,
                             size_t *aNodesSize, size_t *aEdgesSize,
                             size_t *aWeakMapsSize) const {
        *aNodesSize = mNodes.SizeOfExcludingThis(aMallocSizeOf);
        *aEdgesSize = mEdges.SizeOfExcludingThis(aMallocSizeOf);

        // We don't measure what the WeakMappings point to, because the
        // pointers are non-owning.
        *aWeakMapsSize = mWeakMaps.SizeOfExcludingThis(aMallocSizeOf);
    }
};

PtrInfo*
GCGraph::FindNode(void *aPtr)
{
    PtrToNodeEntry *e = static_cast<PtrToNodeEntry*>(PL_DHashTableOperate(&mPtrToNodeMap, aPtr, PL_DHASH_LOOKUP));
    if (!PL_DHASH_ENTRY_IS_BUSY(e)) {
        return nullptr;
    }
    return e->mNode;
}

PtrToNodeEntry*
GCGraph::AddNodeToMap(void *aPtr)
{
    PtrToNodeEntry *e = static_cast<PtrToNodeEntry*>(PL_DHashTableOperate(&mPtrToNodeMap, aPtr, PL_DHASH_ADD));
    if (!e) {
        // Caller should track OOMs
        return nullptr;
    }
    return e;
}

void
GCGraph::RemoveNodeFromMap(void *aPtr)
{
    PL_DHashTableOperate(&mPtrToNodeMap, aPtr, PL_DHASH_REMOVE);
}


static nsISupports *
CanonicalizeXPCOMParticipant(nsISupports *in)
{
    nsISupports* out;
    in->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
                       reinterpret_cast<void**>(&out));
    return out;
}

static inline void
ToParticipant(nsISupports *s, nsXPCOMCycleCollectionParticipant **cp);

static void
CanonicalizeParticipant(void **parti, nsCycleCollectionParticipant **cp)
{
    // If the participant is null, this is an nsISupports participant,
    // so we must QI to get the real participant.

    if (!*cp) {
        nsISupports *nsparti = static_cast<nsISupports*>(*parti);
        nsparti = CanonicalizeXPCOMParticipant(nsparti);
        NS_ASSERTION(nsparti,
                     "Don't add objects that don't participate in collection!");
        nsXPCOMCycleCollectionParticipant *xcp;
        ToParticipant(nsparti, &xcp);
        *parti = nsparti;
        *cp = xcp;
    }
}

struct nsPurpleBufferEntry {
  union {
    void *mObject;                        // when low bit unset
    nsPurpleBufferEntry *mNextInFreeList; // when low bit set
  };

  nsCycleCollectingAutoRefCnt *mRefCnt;

  nsCycleCollectionParticipant *mParticipant; // nullptr for nsISupports
};

class nsCycleCollector;

struct nsPurpleBuffer
{
private:
    struct Block {
        Block *mNext;
        // Try to match the size of a jemalloc bucket, to minimize slop bytes.
        // - On 32-bit platforms sizeof(nsPurpleBufferEntry) is 12, so mEntries
        //   is 16,380 bytes, which leaves 4 bytes for mNext.
        // - On 64-bit platforms sizeof(nsPurpleBufferEntry) is 24, so mEntries
        //   is 32,544 bytes, which leaves 8 bytes for mNext.
        nsPurpleBufferEntry mEntries[1365];

        Block() : mNext(nullptr) {
            // Ensure Block is the right size (see above).
            static_assert(
                sizeof(Block) == 16384 ||       // 32-bit
                sizeof(Block) == 32768,         // 64-bit
                "ill-sized nsPurpleBuffer::Block"
            );
        }

        template <class PurpleVisitor>
        void VisitEntries(nsPurpleBuffer &aBuffer, PurpleVisitor &aVisitor)
        {
            nsPurpleBufferEntry *eEnd = ArrayEnd(mEntries);
            for (nsPurpleBufferEntry *e = mEntries; e != eEnd; ++e) {
                if (!(uintptr_t(e->mObject) & uintptr_t(1))) {
                    aVisitor.Visit(aBuffer, e);
                }
            }
        }
    };
    // This class wraps a linked list of the elements in the purple
    // buffer.

    uint32_t mCount;
    Block mFirstBlock;
    nsPurpleBufferEntry *mFreeList;

public:
    nsPurpleBuffer()
    {
        InitBlocks();
    }

    ~nsPurpleBuffer()
    {
        FreeBlocks();
    }

    template <class PurpleVisitor>
    void VisitEntries(PurpleVisitor &aVisitor)
    {
        for (Block *b = &mFirstBlock; b; b = b->mNext) {
            b->VisitEntries(*this, aVisitor);
        }
    }

    void InitBlocks()
    {
        mCount = 0;
        mFreeList = nullptr;
        StartBlock(&mFirstBlock);
    }

    void StartBlock(Block *aBlock)
    {
        NS_ABORT_IF_FALSE(!mFreeList, "should not have free list");

        // Put all the entries in the block on the free list.
        nsPurpleBufferEntry *entries = aBlock->mEntries;
        mFreeList = entries;
        for (uint32_t i = 1; i < ArrayLength(aBlock->mEntries); ++i) {
            entries[i - 1].mNextInFreeList =
                (nsPurpleBufferEntry*)(uintptr_t(entries + i) | 1);
        }
        entries[ArrayLength(aBlock->mEntries) - 1].mNextInFreeList =
            (nsPurpleBufferEntry*)1;
    }

    void FreeBlocks()
    {
        if (mCount > 0)
            UnmarkRemainingPurple(&mFirstBlock);
        Block *b = mFirstBlock.mNext;
        while (b) {
            if (mCount > 0)
                UnmarkRemainingPurple(b);
            Block *next = b->mNext;
            delete b;
            b = next;
        }
        mFirstBlock.mNext = nullptr;
    }

    struct UnmarkRemainingPurpleVisitor
    {
        void
        Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
        {
            if (aEntry->mRefCnt) {
                aEntry->mRefCnt->RemoveFromPurpleBuffer();
                aEntry->mRefCnt = nullptr;
            }
            aEntry->mObject = nullptr;
            --aBuffer.mCount;
        }
    };

    void UnmarkRemainingPurple(Block *b)
    {
        UnmarkRemainingPurpleVisitor visitor;
        b->VisitEntries(*this, visitor);
    }

    void SelectPointers(GCGraphBuilder &builder);

    // RemoveSkippable removes entries from the purple buffer synchronously
    // (1) if aAsyncSnowWhiteFreeing is false and nsPurpleBufferEntry::mRefCnt is 0 or
    // (2) if the object's nsXPCOMCycleCollectionParticipant::CanSkip() returns true or
    // (3) if nsPurpleBufferEntry::mRefCnt->IsPurple() is false.
    // (4) If removeChildlessNodes is true, then any nodes in the purple buffer
    //     that will have no children in the cycle collector graph will also be
    //     removed. CanSkip() may be run on these children.
    void RemoveSkippable(nsCycleCollector* aCollector,
                         bool removeChildlessNodes,
                         bool aAsyncSnowWhiteFreeing,
                         CC_ForgetSkippableCallback aCb);

    MOZ_ALWAYS_INLINE nsPurpleBufferEntry* NewEntry()
    {
        if (MOZ_UNLIKELY(!mFreeList)) {
            Block *b = new Block;
            StartBlock(b);

            // Add the new block as the second block in the list.
            b->mNext = mFirstBlock.mNext;
            mFirstBlock.mNext = b;
        }

        nsPurpleBufferEntry *e = mFreeList;
        mFreeList = (nsPurpleBufferEntry*)
            (uintptr_t(mFreeList->mNextInFreeList) & ~uintptr_t(1));
        return e;
    }

    MOZ_ALWAYS_INLINE void Put(void *p, nsCycleCollectionParticipant *cp,
                               nsCycleCollectingAutoRefCnt *aRefCnt)
    {
        nsPurpleBufferEntry *e = NewEntry();

        ++mCount;

        e->mObject = p;
        e->mRefCnt = aRefCnt;
        e->mParticipant = cp;
    }

    void Remove(nsPurpleBufferEntry *e)
    {
        MOZ_ASSERT(mCount != 0, "must have entries");

        if (e->mRefCnt) {
            e->mRefCnt->RemoveFromPurpleBuffer();
            e->mRefCnt = nullptr;
        }
        e->mNextInFreeList =
            (nsPurpleBufferEntry*)(uintptr_t(mFreeList) | uintptr_t(1));
        mFreeList = e;

        --mCount;
    }

    uint32_t Count() const
    {
        return mCount;
    }

    size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
    {
        size_t n = 0;

        // Don't measure mFirstBlock because it's within |this|.
        const Block *block = mFirstBlock.mNext;
        while (block) {
            n += aMallocSizeOf(block);
            block = block->mNext;
        }

        // mFreeList is deliberately not measured because it points into
        // the purple buffer, which is within mFirstBlock and thus within |this|.
        //
        // We also don't measure the things pointed to by mEntries[] because
        // those pointers are non-owning.

        return n;
    }
};

static bool
AddPurpleRoot(GCGraphBuilder &aBuilder, void *aRoot, nsCycleCollectionParticipant *aParti);

struct SelectPointersVisitor
{
    SelectPointersVisitor(GCGraphBuilder &aBuilder)
        : mBuilder(aBuilder)
    {}

    void
    Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
    {
        MOZ_ASSERT(aEntry->mObject, "Null object in purple buffer");
        MOZ_ASSERT(aEntry->mRefCnt->get() != 0,
                   "SelectPointersVisitor: snow-white object in the purple buffer");
        if (!aEntry->mRefCnt->IsPurple() ||
            AddPurpleRoot(mBuilder, aEntry->mObject, aEntry->mParticipant)) {
            aBuffer.Remove(aEntry);
        }
    }

private:
    GCGraphBuilder &mBuilder;
};

void
nsPurpleBuffer::SelectPointers(GCGraphBuilder &aBuilder)
{
    SelectPointersVisitor visitor(aBuilder);
    VisitEntries(visitor);

    NS_ASSERTION(mCount == 0, "AddPurpleRoot failed");
    if (mCount == 0) {
        FreeBlocks();
        InitBlocks();
    }
}

enum ccPhase {
    IdlePhase,
    GraphBuildingPhase,
    ScanAndCollectWhitePhase,
    CleanupPhase
};

enum ccType {
    ScheduledCC, /* Automatically triggered, based on time or the purple buffer. */
    ManualCC,    /* Explicitly triggered. */
    ShutdownCC   /* Shutdown CC, used for finding leaks. */
};

#ifdef MOZ_NUWA_PROCESS
#include "ipc/Nuwa.h"
#endif

////////////////////////////////////////////////////////////////////////
// Top level structure for the cycle collector.
////////////////////////////////////////////////////////////////////////

typedef js::SliceBudget SliceBudget;

class nsCycleCollector : public nsIMemoryReporter
{
    NS_DECL_ISUPPORTS
    NS_DECL_NSIMEMORYREPORTER

    bool mActivelyCollecting;
    // mScanInProgress should be false when we're collecting white objects.
    bool mScanInProgress;
    CycleCollectorResults mResults;
    TimeStamp mCollectionStart;

    CycleCollectedJSRuntime *mJSRuntime;

    ccPhase mIncrementalPhase;
    GCGraph mGraph;
    nsAutoPtr<GCGraphBuilder> mBuilder;
    nsAutoPtr<NodePool::Enumerator> mCurrNode;
    nsCOMPtr<nsICycleCollectorListener> mListener;

    nsIThread* mThread;

    nsCycleCollectorParams mParams;

    uint32_t mWhiteNodeCount;

    CC_BeforeUnlinkCallback mBeforeUnlinkCB;
    CC_ForgetSkippableCallback mForgetSkippableCB;

    nsPurpleBuffer mPurpleBuf;

    uint32_t mUnmergedNeeded;
    uint32_t mMergedInARow;

public:
    nsCycleCollector();
    virtual ~nsCycleCollector();

    void RegisterJSRuntime(CycleCollectedJSRuntime *aJSRuntime);
    void ForgetJSRuntime();

    void SetBeforeUnlinkCallback(CC_BeforeUnlinkCallback aBeforeUnlinkCB)
    {
        CheckThreadSafety();
        mBeforeUnlinkCB = aBeforeUnlinkCB;
    }

    void SetForgetSkippableCallback(CC_ForgetSkippableCallback aForgetSkippableCB)
    {
        CheckThreadSafety();
        mForgetSkippableCB = aForgetSkippableCB;
    }

    void Suspect(void *n, nsCycleCollectionParticipant *cp,
                 nsCycleCollectingAutoRefCnt *aRefCnt);
    uint32_t SuspectedCount();
    void ForgetSkippable(bool aRemoveChildlessNodes, bool aAsyncSnowWhiteFreeing);
    bool FreeSnowWhite(bool aUntilNoSWInPurpleBuffer);

    // This method assumes its argument is already canonicalized.
    void RemoveObjectFromGraph(void *aPtr);

    void PrepareForGarbageCollection();

    bool Collect(ccType aCCType,
                 SliceBudget &aBudget,
                 nsICycleCollectorListener *aManualListener);
    void Shutdown();

    void SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                             size_t *aObjectSize,
                             size_t *aGraphNodesSize,
                             size_t *aGraphEdgesSize,
                             size_t *aWeakMapsSize,
                             size_t *aPurpleBufferSize) const;

private:
    void CheckThreadSafety();
    void ShutdownCollect();

    void FixGrayBits(bool aForceGC);
    bool ShouldMergeZones(ccType aCCType);

    void BeginCollection(ccType aCCType, nsICycleCollectorListener *aManualListener);
    void MarkRoots(SliceBudget &aBudget);
    void ScanRoots();
    void ScanWeakMaps();

    // returns whether anything was collected
    bool CollectWhite();

    void CleanupAfterCollection();
};

NS_IMPL_ISUPPORTS1(nsCycleCollector, nsIMemoryReporter)

/**
 * GraphWalker is templatized over a Visitor class that must provide
 * the following two methods:
 *
 * bool ShouldVisitNode(PtrInfo const *pi);
 * void VisitNode(PtrInfo *pi);
 */
template <class Visitor>
class GraphWalker
{
private:
    Visitor mVisitor;

    void DoWalk(nsDeque &aQueue);

    void CheckedPush(nsDeque &aQueue, PtrInfo *pi)
    {
        CC_AbortIfNull(pi);
        if (!aQueue.Push(pi, fallible_t())) {
            mVisitor.Failed();
        }
    }

public:
    void Walk(PtrInfo *s0);
    void WalkFromRoots(GCGraph &aGraph);
    // copy-constructing the visitor should be cheap, and less
    // indirection than using a reference
    GraphWalker(const Visitor aVisitor) : mVisitor(aVisitor) {}
};


////////////////////////////////////////////////////////////////////////
// The static collector struct
////////////////////////////////////////////////////////////////////////

struct CollectorData {
  nsRefPtr<nsCycleCollector> mCollector;
  CycleCollectedJSRuntime* mRuntime;
};

static mozilla::ThreadLocal<CollectorData*> sCollectorData;

////////////////////////////////////////////////////////////////////////
// Utility functions
////////////////////////////////////////////////////////////////////////

MOZ_NEVER_INLINE static void
Fault(const char *msg, const void *ptr=nullptr)
{
    if (ptr)
        printf("Fault in cycle collector: %s (ptr: %p)\n", msg, ptr);
    else
        printf("Fault in cycle collector: %s\n", msg);

    NS_RUNTIMEABORT("cycle collector fault");
}

static void
Fault(const char *msg, PtrInfo *pi)
{
    Fault(msg, pi->mPointer);
}

static inline void
ToParticipant(nsISupports *s, nsXPCOMCycleCollectionParticipant **cp)
{
    // We use QI to move from an nsISupports to an
    // nsXPCOMCycleCollectionParticipant, which is a per-class singleton helper
    // object that implements traversal and unlinking logic for the nsISupports
    // in question.
    CallQueryInterface(s, cp);
}

template <class Visitor>
MOZ_NEVER_INLINE void
GraphWalker<Visitor>::Walk(PtrInfo *s0)
{
    nsDeque queue;
    CheckedPush(queue, s0);
    DoWalk(queue);
}

template <class Visitor>
MOZ_NEVER_INLINE void
GraphWalker<Visitor>::WalkFromRoots(GCGraph& aGraph)
{
    nsDeque queue;
    NodePool::Enumerator etor(aGraph.mNodes);
    for (uint32_t i = 0; i < aGraph.mRootCount; ++i) {
        CheckedPush(queue, etor.GetNext());
    }
    DoWalk(queue);
}

template <class Visitor>
MOZ_NEVER_INLINE void
GraphWalker<Visitor>::DoWalk(nsDeque &aQueue)
{
    // Use a aQueue to match the breadth-first traversal used when we
    // built the graph, for hopefully-better locality.
    while (aQueue.GetSize() > 0) {
        PtrInfo *pi = static_cast<PtrInfo*>(aQueue.PopFront());
        CC_AbortIfNull(pi);

        if (pi->mParticipant && mVisitor.ShouldVisitNode(pi)) {
            mVisitor.VisitNode(pi);
            for (EdgePool::Iterator child = pi->FirstChild(),
                                child_end = pi->LastChild();
                 child != child_end; ++child) {
                CheckedPush(aQueue, *child);
            }
        }
    }
}

struct CCGraphDescriber : public LinkedListElement<CCGraphDescriber>
{
  CCGraphDescriber()
  : mAddress("0x"), mCnt(0), mType(eUnknown) {}

  enum Type
  {
    eRefCountedObject,
    eGCedObject,
    eGCMarkedObject,
    eEdge,
    eRoot,
    eGarbage,
    eUnknown
  };

  nsCString mAddress;
  nsCString mName;
  nsCString mCompartmentOrToAddress;
  uint32_t mCnt;
  Type mType;
};

class nsCycleCollectorLogger MOZ_FINAL : public nsICycleCollectorListener
{
public:
    nsCycleCollectorLogger() :
      mStream(nullptr), mWantAllTraces(false),
      mDisableLog(false), mWantAfterProcessing(false)
    {
    }
    ~nsCycleCollectorLogger()
    {
        ClearDescribers();
        if (mStream) {
            MozillaUnRegisterDebugFILE(mStream);
            fclose(mStream);
        }
    }
    NS_DECL_ISUPPORTS

    void SetAllTraces()
    {
        mWantAllTraces = true;
    }

    NS_IMETHOD AllTraces(nsICycleCollectorListener** aListener)
    {
        SetAllTraces();
        NS_ADDREF(*aListener = this);
        return NS_OK;
    }

    NS_IMETHOD GetWantAllTraces(bool* aAllTraces)
    {
        *aAllTraces = mWantAllTraces;
        return NS_OK;
    }

    NS_IMETHOD GetDisableLog(bool* aDisableLog)
    {
        *aDisableLog = mDisableLog;
        return NS_OK;
    }

    NS_IMETHOD SetDisableLog(bool aDisableLog)
    {
        mDisableLog = aDisableLog;
        return NS_OK;
    }

    NS_IMETHOD GetWantAfterProcessing(bool* aWantAfterProcessing)
    {
        *aWantAfterProcessing = mWantAfterProcessing;
        return NS_OK;
    }

    NS_IMETHOD SetWantAfterProcessing(bool aWantAfterProcessing)
    {
        mWantAfterProcessing = aWantAfterProcessing;
        return NS_OK;
    }

    NS_IMETHOD GetFilenameIdentifier(nsAString& aIdentifier)
    {
        aIdentifier = mFilenameIdentifier;
        return NS_OK;
    }

    NS_IMETHOD SetFilenameIdentifier(const nsAString& aIdentifier)
    {
        mFilenameIdentifier = aIdentifier;
        return NS_OK;
    }

    NS_IMETHOD Begin()
    {
        mCurrentAddress.AssignLiteral("0x");
        ClearDescribers();
        if (mDisableLog) {
            return NS_OK;
        }

        // Initially create the log in a file starting with
        // "incomplete-gc-edges".  We'll move the file and strip off the
        // "incomplete-" once the dump completes.  (We do this because we don't
        // want scripts which poll the filesystem looking for gc/cc dumps to
        // grab a file before we're finished writing to it.)
        nsCOMPtr<nsIFile> gcLogFile = CreateTempFile("incomplete-gc-edges");
        if (NS_WARN_IF(!gcLogFile))
            return NS_ERROR_UNEXPECTED;

        // Dump the JS heap.
        FILE* gcLogANSIFile = nullptr;
        gcLogFile->OpenANSIFileDesc("w", &gcLogANSIFile);
        if (NS_WARN_IF(!gcLogANSIFile))
            return NS_ERROR_UNEXPECTED;
        MozillaRegisterDebugFILE(gcLogANSIFile);
        CollectorData *data = sCollectorData.get();
        if (data && data->mRuntime)
            data->mRuntime->DumpJSHeap(gcLogANSIFile);
        MozillaUnRegisterDebugFILE(gcLogANSIFile);
        fclose(gcLogANSIFile);

        // Strip off "incomplete-".
        nsCOMPtr<nsIFile> gcLogFileFinalDestination =
            CreateTempFile("gc-edges");
        if (NS_WARN_IF(!gcLogFileFinalDestination))
            return NS_ERROR_UNEXPECTED;

        nsAutoString gcLogFileFinalDestinationName;
        gcLogFileFinalDestination->GetLeafName(gcLogFileFinalDestinationName);
        if (NS_WARN_IF(gcLogFileFinalDestinationName.IsEmpty()))
            return NS_ERROR_UNEXPECTED;

        gcLogFile->MoveTo(/* directory */ nullptr, gcLogFileFinalDestinationName);

        // Log to the error console.
        nsCOMPtr<nsIConsoleService> cs =
            do_GetService(NS_CONSOLESERVICE_CONTRACTID);
        if (cs) {
            nsAutoString gcLogPath;
            gcLogFileFinalDestination->GetPath(gcLogPath);

            nsString msg = NS_LITERAL_STRING("Garbage Collector log dumped to ") +
                           gcLogPath;
            cs->LogStringMessage(msg.get());
        }

        // Open a file for dumping the CC graph.  We again prefix with
        // "incomplete-".
        mOutFile = CreateTempFile("incomplete-cc-edges");
        if (NS_WARN_IF(!mOutFile))
            return NS_ERROR_UNEXPECTED;
        MOZ_ASSERT(!mStream);
        mOutFile->OpenANSIFileDesc("w", &mStream);
        if (NS_WARN_IF(!mStream))
            return NS_ERROR_UNEXPECTED;
        MozillaRegisterDebugFILE(mStream);

        fprintf(mStream, "# WantAllTraces=%s\n", mWantAllTraces ? "true" : "false");

        return NS_OK;
    }
    NS_IMETHOD NoteRefCountedObject(uint64_t aAddress, uint32_t refCount,
                                    const char *aObjectDescription)
    {
        if (!mDisableLog) {
            fprintf(mStream, "%p [rc=%u] %s\n", (void*)aAddress, refCount,
                    aObjectDescription);
        }
        if (mWantAfterProcessing) {
            CCGraphDescriber* d =  new CCGraphDescriber();
            mDescribers.insertBack(d);
            mCurrentAddress.AssignLiteral("0x");
            mCurrentAddress.AppendInt(aAddress, 16);
            d->mType = CCGraphDescriber::eRefCountedObject;
            d->mAddress = mCurrentAddress;
            d->mCnt = refCount;
            d->mName.Append(aObjectDescription);
        }
        return NS_OK;
    }
    NS_IMETHOD NoteGCedObject(uint64_t aAddress, bool aMarked,
                              const char *aObjectDescription,
                              uint64_t aCompartmentAddress)
    {
        if (!mDisableLog) {
            fprintf(mStream, "%p [gc%s] %s\n", (void*)aAddress,
                    aMarked ? ".marked" : "", aObjectDescription);
        }
        if (mWantAfterProcessing) {
            CCGraphDescriber* d =  new CCGraphDescriber();
            mDescribers.insertBack(d);
            mCurrentAddress.AssignLiteral("0x");
            mCurrentAddress.AppendInt(aAddress, 16);
            d->mType = aMarked ? CCGraphDescriber::eGCMarkedObject :
                                 CCGraphDescriber::eGCedObject;
            d->mAddress = mCurrentAddress;
            d->mName.Append(aObjectDescription);
            if (aCompartmentAddress) {
                d->mCompartmentOrToAddress.AssignLiteral("0x");
                d->mCompartmentOrToAddress.AppendInt(aCompartmentAddress, 16);
            } else {
                d->mCompartmentOrToAddress.SetIsVoid(true);
            }
        }
        return NS_OK;
    }
    NS_IMETHOD NoteEdge(uint64_t aToAddress, const char *aEdgeName)
    {
        if (!mDisableLog) {
            fprintf(mStream, "> %p %s\n", (void*)aToAddress, aEdgeName);
        }
        if (mWantAfterProcessing) {
            CCGraphDescriber* d =  new CCGraphDescriber();
            mDescribers.insertBack(d);
            d->mType = CCGraphDescriber::eEdge;
            d->mAddress = mCurrentAddress;
            d->mCompartmentOrToAddress.AssignLiteral("0x");
            d->mCompartmentOrToAddress.AppendInt(aToAddress, 16);
            d->mName.Append(aEdgeName);
        }
        return NS_OK;
    }
    NS_IMETHOD NoteWeakMapEntry(uint64_t aMap, uint64_t aKey,
                                uint64_t aKeyDelegate, uint64_t aValue)
    {
        if (!mDisableLog) {
            fprintf(mStream, "WeakMapEntry map=%p key=%p keyDelegate=%p value=%p\n",
                    (void*)aMap, (void*)aKey, (void*)aKeyDelegate, (void*)aValue);
        }
        // We don't support after-processing for weak map entries.
        return NS_OK;
    }
    NS_IMETHOD BeginResults()
    {
        if (!mDisableLog) {
            fputs("==========\n", mStream);
        }
        return NS_OK;
    }
    NS_IMETHOD DescribeRoot(uint64_t aAddress, uint32_t aKnownEdges)
    {
        if (!mDisableLog) {
            fprintf(mStream, "%p [known=%u]\n", (void*)aAddress, aKnownEdges);
        }
        if (mWantAfterProcessing) {
            CCGraphDescriber* d =  new CCGraphDescriber();
            mDescribers.insertBack(d);
            d->mType = CCGraphDescriber::eRoot;
            d->mAddress.AppendInt(aAddress, 16);
            d->mCnt = aKnownEdges;
        }
        return NS_OK;
    }
    NS_IMETHOD DescribeGarbage(uint64_t aAddress)
    {
        if (!mDisableLog) {
            fprintf(mStream, "%p [garbage]\n", (void*)aAddress);
        }
        if (mWantAfterProcessing) {
            CCGraphDescriber* d =  new CCGraphDescriber();
            mDescribers.insertBack(d);
            d->mType = CCGraphDescriber::eGarbage;
            d->mAddress.AppendInt(aAddress, 16);
        }
        return NS_OK;
    }
    NS_IMETHOD End()
    {
        if (!mDisableLog) {
            MOZ_ASSERT(mStream);
            MOZ_ASSERT(mOutFile);

            MozillaUnRegisterDebugFILE(mStream);
            fclose(mStream);
            mStream = nullptr;

            // Strip off "incomplete-" from the log file's name.
            nsCOMPtr<nsIFile> logFileFinalDestination =
                CreateTempFile("cc-edges");
            if (NS_WARN_IF(!logFileFinalDestination))
                return NS_ERROR_UNEXPECTED;

            nsAutoString logFileFinalDestinationName;
            logFileFinalDestination->GetLeafName(logFileFinalDestinationName);
            if (NS_WARN_IF(logFileFinalDestinationName.IsEmpty()))
                return NS_ERROR_UNEXPECTED;

            mOutFile->MoveTo(/* directory = */ nullptr,
                             logFileFinalDestinationName);
            mOutFile = nullptr;

            // Log to the error console.
            nsCOMPtr<nsIConsoleService> cs =
                do_GetService(NS_CONSOLESERVICE_CONTRACTID);
            if (cs) {
                nsAutoString ccLogPath;
                logFileFinalDestination->GetPath(ccLogPath);

                nsString msg = NS_LITERAL_STRING("Cycle Collector log dumped to ") +
                               ccLogPath;
                cs->LogStringMessage(msg.get());
            }
        }
        return NS_OK;
    }
    NS_IMETHOD ProcessNext(nsICycleCollectorHandler* aHandler,
                           bool* aCanContinue)
    {
        if (NS_WARN_IF(!aHandler) || NS_WARN_IF(!mWantAfterProcessing))
            return NS_ERROR_UNEXPECTED;
        CCGraphDescriber* d = mDescribers.popFirst();
        if (d) {
            switch (d->mType) {
                case CCGraphDescriber::eRefCountedObject:
                    aHandler->NoteRefCountedObject(d->mAddress,
                                                   d->mCnt,
                                                   d->mName);
                    break;
                case CCGraphDescriber::eGCedObject:
                case CCGraphDescriber::eGCMarkedObject:
                    aHandler->NoteGCedObject(d->mAddress,
                                             d->mType ==
                                               CCGraphDescriber::eGCMarkedObject,
                                             d->mName,
                                             d->mCompartmentOrToAddress);
                    break;
                case CCGraphDescriber::eEdge:
                    aHandler->NoteEdge(d->mAddress,
                                       d->mCompartmentOrToAddress,
                                       d->mName);
                    break;
                case CCGraphDescriber::eRoot:
                    aHandler->DescribeRoot(d->mAddress,
                                           d->mCnt);
                    break;
                case CCGraphDescriber::eGarbage:
                    aHandler->DescribeGarbage(d->mAddress);
                    break;
                case CCGraphDescriber::eUnknown:
                    NS_NOTREACHED("CCGraphDescriber::eUnknown");
                    break;
            }
            delete d;
        }
        if (!(*aCanContinue = !mDescribers.isEmpty())) {
            mCurrentAddress.AssignLiteral("0x");
        }
        return NS_OK;
    }
private:
    /**
     * Create a new file named something like aPrefix.$PID.$IDENTIFIER.log in
     * $MOZ_CC_LOG_DIRECTORY or in the system's temp directory.  No existing
     * file will be overwritten; if aPrefix.$PID.$IDENTIFIER.log exists, we'll
     * try a file named something like aPrefix.$PID.$IDENTIFIER-1.log, and so
     * on.
     */
    already_AddRefed<nsIFile>
    CreateTempFile(const char* aPrefix)
    {
        nsPrintfCString filename("%s.%d%s%s.log",
            aPrefix,
            base::GetCurrentProcId(),
            mFilenameIdentifier.IsEmpty() ? "" : ".",
            NS_ConvertUTF16toUTF8(mFilenameIdentifier).get());

        // Get the log directory either from $MOZ_CC_LOG_DIRECTORY or from
        // the fallback directories in OpenTempFile.  We don't use an nsCOMPtr
        // here because OpenTempFile uses an in/out param and getter_AddRefs
        // wouldn't work.
        nsIFile* logFile = nullptr;
        if (char* env = PR_GetEnv("MOZ_CC_LOG_DIRECTORY")) {
            NS_NewNativeLocalFile(nsCString(env), /* followLinks = */ true,
                                  &logFile);
        }
        nsresult rv = nsMemoryInfoDumper::OpenTempFile(filename, &logFile);
        if (NS_FAILED(rv)) {
          NS_IF_RELEASE(logFile);
          return nullptr;
        }

        return dont_AddRef(logFile);
    }

    void ClearDescribers()
    {
      CCGraphDescriber* d;
      while((d = mDescribers.popFirst())) {
        delete d;
      }
    }

    FILE *mStream;
    nsCOMPtr<nsIFile> mOutFile;
    bool mWantAllTraces;
    bool mDisableLog;
    bool mWantAfterProcessing;
    nsString mFilenameIdentifier;
    nsCString mCurrentAddress;
    mozilla::LinkedList<CCGraphDescriber> mDescribers;
};

NS_IMPL_ISUPPORTS1(nsCycleCollectorLogger, nsICycleCollectorListener)

nsresult
nsCycleCollectorLoggerConstructor(nsISupports* aOuter,
                                  const nsIID& aIID,
                                  void* *aInstancePtr)
{
    if (NS_WARN_IF(aOuter))
        return NS_ERROR_NO_AGGREGATION;

    nsISupports *logger = new nsCycleCollectorLogger();

    return logger->QueryInterface(aIID, aInstancePtr);
}

////////////////////////////////////////////////////////////////////////
// Bacon & Rajan's |MarkRoots| routine.
////////////////////////////////////////////////////////////////////////

class GCGraphBuilder : public nsCycleCollectionTraversalCallback,
                       public nsCycleCollectionNoteRootCallback
{
private:
    GCGraph &mGraph;
    CycleCollectorResults &mResults;
    NodePool::Builder mNodeBuilder;
    EdgePool::Builder mEdgeBuilder;
    PtrInfo *mCurrPi;
    nsCycleCollectionParticipant *mJSParticipant;
    nsCycleCollectionParticipant *mJSZoneParticipant;
    nsCString mNextEdgeName;
    nsICycleCollectorListener *mListener;
    bool mMergeZones;
    bool mRanOutOfMemory;

public:
    GCGraphBuilder(GCGraph &aGraph,
                   CycleCollectorResults &aResults,
                   CycleCollectedJSRuntime *aJSRuntime,
                   nsICycleCollectorListener *aListener,
                   bool aMergeZones);
    virtual ~GCGraphBuilder();

    bool WantAllTraces() const
    {
        return nsCycleCollectionNoteRootCallback::WantAllTraces();
    }

    PtrInfo* AddNode(void *aPtr, nsCycleCollectionParticipant *aParticipant);
    PtrInfo* AddWeakMapNode(void* node);
    void Traverse(PtrInfo* aPtrInfo);
    void SetLastChild();

    bool RanOutOfMemory() const { return mRanOutOfMemory; }

private:
    void DescribeNode(uint32_t refCount, const char *objName)
    {
        mCurrPi->mRefCount = refCount;
    }

public:
    // nsCycleCollectionNoteRootCallback methods.
    NS_IMETHOD_(void) NoteXPCOMRoot(nsISupports *root);
    NS_IMETHOD_(void) NoteJSRoot(void *root);
    NS_IMETHOD_(void) NoteNativeRoot(void *root, nsCycleCollectionParticipant *participant);
    NS_IMETHOD_(void) NoteWeakMapping(void *map, void *key, void *kdelegate, void *val);

    // nsCycleCollectionTraversalCallback methods.
    NS_IMETHOD_(void) DescribeRefCountedNode(nsrefcnt refCount,
                                             const char *objName);
    NS_IMETHOD_(void) DescribeGCedNode(bool isMarked, const char *objName,
                                       uint64_t aCompartmentAddress);

    NS_IMETHOD_(void) NoteXPCOMChild(nsISupports *child);
    NS_IMETHOD_(void) NoteJSChild(void *child);
    NS_IMETHOD_(void) NoteNativeChild(void *child,
                                      nsCycleCollectionParticipant *participant);
    NS_IMETHOD_(void) NoteNextEdgeName(const char* name);

private:
    NS_IMETHOD_(void) NoteRoot(void *root,
                               nsCycleCollectionParticipant *participant)
    {
        MOZ_ASSERT(root);
        MOZ_ASSERT(participant);

        if (!participant->CanSkipInCC(root) || MOZ_UNLIKELY(WantAllTraces())) {
            AddNode(root, participant);
        }
    }

    NS_IMETHOD_(void) NoteChild(void *child, nsCycleCollectionParticipant *cp,
                                nsCString edgeName)
    {
        PtrInfo *childPi = AddNode(child, cp);
        if (!childPi)
            return;
        mEdgeBuilder.Add(childPi);
        if (mListener) {
            mListener->NoteEdge((uint64_t)child, edgeName.get());
        }
        ++childPi->mInternalRefs;
    }

    JS::Zone *MergeZone(void *gcthing) {
        if (!mMergeZones) {
            return nullptr;
        }
        JS::Zone *zone = JS::GetGCThingZone(gcthing);
        if (js::IsSystemZone(zone)) {
            return nullptr;
        }
        return zone;
    }
};

GCGraphBuilder::GCGraphBuilder(GCGraph &aGraph,
                               CycleCollectorResults &aResults,
                               CycleCollectedJSRuntime *aJSRuntime,
                               nsICycleCollectorListener *aListener,
                               bool aMergeZones)
    : mGraph(aGraph),
      mResults(aResults),
      mNodeBuilder(aGraph.mNodes),
      mEdgeBuilder(aGraph.mEdges),
      mJSParticipant(nullptr),
      mJSZoneParticipant(nullptr),
      mListener(aListener),
      mMergeZones(aMergeZones),
      mRanOutOfMemory(false)
{
    if (aJSRuntime) {
        mJSParticipant = aJSRuntime->GCThingParticipant();
        mJSZoneParticipant = aJSRuntime->ZoneParticipant();
    }

    uint32_t flags = 0;
    if (!flags && mListener) {
        flags = nsCycleCollectionTraversalCallback::WANT_DEBUG_INFO;
        bool all = false;
        mListener->GetWantAllTraces(&all);
        if (all) {
            flags |= nsCycleCollectionTraversalCallback::WANT_ALL_TRACES;
            mWantAllTraces = true; // for nsCycleCollectionNoteRootCallback
        }
    }

    mFlags |= flags;

    mMergeZones = mMergeZones && MOZ_LIKELY(!WantAllTraces());

    MOZ_ASSERT(nsCycleCollectionNoteRootCallback::WantAllTraces() ==
               nsCycleCollectionTraversalCallback::WantAllTraces());
}

GCGraphBuilder::~GCGraphBuilder()
{
}

PtrInfo*
GCGraphBuilder::AddNode(void *aPtr, nsCycleCollectionParticipant *aParticipant)
{
    PtrToNodeEntry *e = mGraph.AddNodeToMap(aPtr);
    if (!e) {
        mRanOutOfMemory = true;
        return nullptr;
    }

    PtrInfo *result;
    if (!e->mNode) {
        // New entry.
        result = mNodeBuilder.Add(aPtr, aParticipant);
        e->mNode = result;
        NS_ASSERTION(result, "mNodeBuilder.Add returned null");
    } else {
        result = e->mNode;
        MOZ_ASSERT(result->mParticipant == aParticipant,
                   "nsCycleCollectionParticipant shouldn't change!");
    }
    return result;
}

MOZ_NEVER_INLINE void
GCGraphBuilder::Traverse(PtrInfo* aPtrInfo)
{
    mCurrPi = aPtrInfo;

    mCurrPi->SetFirstChild(mEdgeBuilder.Mark());

    if (!aPtrInfo->mParticipant) {
        return;
    }

    nsresult rv = aPtrInfo->mParticipant->Traverse(aPtrInfo->mPointer, *this);
    if (NS_FAILED(rv)) {
        Fault("script pointer traversal failed", aPtrInfo);
    }
}

void
GCGraphBuilder::SetLastChild()
{
    mCurrPi->SetLastChild(mEdgeBuilder.Mark());
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteXPCOMRoot(nsISupports *root)
{
    root = CanonicalizeXPCOMParticipant(root);
    NS_ASSERTION(root,
                 "Don't add objects that don't participate in collection!");

    nsXPCOMCycleCollectionParticipant *cp;
    ToParticipant(root, &cp);

    NoteRoot(root, cp);
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteJSRoot(void *root)
{
    if (JS::Zone *zone = MergeZone(root)) {
        NoteRoot(zone, mJSZoneParticipant);
    } else {
        NoteRoot(root, mJSParticipant);
    }
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteNativeRoot(void *root, nsCycleCollectionParticipant *participant)
{
    NoteRoot(root, participant);
}

NS_IMETHODIMP_(void)
GCGraphBuilder::DescribeRefCountedNode(nsrefcnt refCount, const char *objName)
{
    if (refCount == 0)
        Fault("zero refcount", mCurrPi);
    if (refCount == UINT32_MAX)
        Fault("overflowing refcount", mCurrPi);
    mResults.mVisitedRefCounted++;

    if (mListener) {
        mListener->NoteRefCountedObject((uint64_t)mCurrPi->mPointer, refCount,
                                        objName);
    }

    DescribeNode(refCount, objName);
}

NS_IMETHODIMP_(void)
GCGraphBuilder::DescribeGCedNode(bool isMarked, const char *objName,
                                 uint64_t aCompartmentAddress)
{
    uint32_t refCount = isMarked ? UINT32_MAX : 0;
    mResults.mVisitedGCed++;

    if (mListener) {
        mListener->NoteGCedObject((uint64_t)mCurrPi->mPointer, isMarked,
                                  objName, aCompartmentAddress);
    }

    DescribeNode(refCount, objName);
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteXPCOMChild(nsISupports *child)
{
    nsCString edgeName;
    if (WantDebugInfo()) {
        edgeName.Assign(mNextEdgeName);
        mNextEdgeName.Truncate();
    }
    if (!child || !(child = CanonicalizeXPCOMParticipant(child)))
        return;

    nsXPCOMCycleCollectionParticipant *cp;
    ToParticipant(child, &cp);
    if (cp && (!cp->CanSkipThis(child) || WantAllTraces())) {
        NoteChild(child, cp, edgeName);
    }
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteNativeChild(void *child,
                                nsCycleCollectionParticipant *participant)
{
    nsCString edgeName;
    if (WantDebugInfo()) {
        edgeName.Assign(mNextEdgeName);
        mNextEdgeName.Truncate();
    }
    if (!child)
        return;

    MOZ_ASSERT(participant, "Need a nsCycleCollectionParticipant!");
    NoteChild(child, participant, edgeName);
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteJSChild(void *child)
{
    if (!child) {
        return;
    }

    nsCString edgeName;
    if (MOZ_UNLIKELY(WantDebugInfo())) {
        edgeName.Assign(mNextEdgeName);
        mNextEdgeName.Truncate();
    }

    if (xpc_GCThingIsGrayCCThing(child) || MOZ_UNLIKELY(WantAllTraces())) {
        if (JS::Zone *zone = MergeZone(child)) {
            NoteChild(zone, mJSZoneParticipant, edgeName);
        } else {
            NoteChild(child, mJSParticipant, edgeName);
        }
    }
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteNextEdgeName(const char* name)
{
    if (WantDebugInfo()) {
        mNextEdgeName = name;
    }
}

PtrInfo*
GCGraphBuilder::AddWeakMapNode(void *node)
{
    MOZ_ASSERT(node, "Weak map node should be non-null.");

    if (!xpc_GCThingIsGrayCCThing(node) && !WantAllTraces())
        return nullptr;

    if (JS::Zone *zone = MergeZone(node)) {
        return AddNode(zone, mJSZoneParticipant);
    } else {
        return AddNode(node, mJSParticipant);
    }
}

NS_IMETHODIMP_(void)
GCGraphBuilder::NoteWeakMapping(void *map, void *key, void *kdelegate, void *val)
{
    // Don't try to optimize away the entry here, as we've already attempted to
    // do that in TraceWeakMapping in nsXPConnect.
    WeakMapping *mapping = mGraph.mWeakMaps.AppendElement();
    mapping->mMap = map ? AddWeakMapNode(map) : nullptr;
    mapping->mKey = key ? AddWeakMapNode(key) : nullptr;
    mapping->mKeyDelegate = kdelegate ? AddWeakMapNode(kdelegate) : mapping->mKey;
    mapping->mVal = val ? AddWeakMapNode(val) : nullptr;

    if (mListener) {
        mListener->NoteWeakMapEntry((uint64_t)map, (uint64_t)key,
                                    (uint64_t)kdelegate, (uint64_t)val);
    }
}

static bool
AddPurpleRoot(GCGraphBuilder &aBuilder, void *aRoot, nsCycleCollectionParticipant *aParti)
{
    CanonicalizeParticipant(&aRoot, &aParti);

    if (aBuilder.WantAllTraces() || !aParti->CanSkipInCC(aRoot)) {
        PtrInfo *pinfo = aBuilder.AddNode(aRoot, aParti);
        if (!pinfo) {
            return false;
        }
    }

    return true;
}

// MayHaveChild() will be false after a Traverse if the object does
// not have any children the CC will visit.
class ChildFinder : public nsCycleCollectionTraversalCallback
{
public:
    ChildFinder() : mMayHaveChild(false) {}

    // The logic of the Note*Child functions must mirror that of their
    // respective functions in GCGraphBuilder.
    NS_IMETHOD_(void) NoteXPCOMChild(nsISupports *child);
    NS_IMETHOD_(void) NoteNativeChild(void *child,
                                      nsCycleCollectionParticipant *helper);
    NS_IMETHOD_(void) NoteJSChild(void *child);

    NS_IMETHOD_(void) DescribeRefCountedNode(nsrefcnt refcount,
                                             const char *objname) {}
    NS_IMETHOD_(void) DescribeGCedNode(bool ismarked,
                                       const char *objname,
                                       uint64_t aCompartmentAddress) {}
    NS_IMETHOD_(void) NoteNextEdgeName(const char* name) {}
    bool MayHaveChild() {
        return mMayHaveChild;
    }
private:
    bool mMayHaveChild;
};

NS_IMETHODIMP_(void)
ChildFinder::NoteXPCOMChild(nsISupports *child)
{
    if (!child || !(child = CanonicalizeXPCOMParticipant(child)))
        return;
    nsXPCOMCycleCollectionParticipant *cp;
    ToParticipant(child, &cp);
    if (cp && !cp->CanSkip(child, true))
        mMayHaveChild = true;
}

NS_IMETHODIMP_(void)
ChildFinder::NoteNativeChild(void *child,
                             nsCycleCollectionParticipant *helper)
{
    if (child)
        mMayHaveChild = true;
}

NS_IMETHODIMP_(void)
ChildFinder::NoteJSChild(void *child)
{
    if (child && xpc_GCThingIsGrayCCThing(child)) {
        mMayHaveChild = true;
    }
}

static bool
MayHaveChild(void *o, nsCycleCollectionParticipant* cp)
{
    ChildFinder cf;
    cp->Traverse(o, cf);
    return cf.MayHaveChild();
}

struct SnowWhiteObject
{
  void* mPointer;
  nsCycleCollectionParticipant* mParticipant;
  nsCycleCollectingAutoRefCnt* mRefCnt;
};

class SnowWhiteKiller
{
public:
    SnowWhiteKiller(nsCycleCollector *aCollector, uint32_t aMaxCount)
        : mCollector(aCollector)
    {
        MOZ_ASSERT(mCollector, "Calling SnowWhiteKiller after nsCC went away");
        while (true) {
            if (mObjects.SetCapacity(aMaxCount)) {
                break;
            }
            if (aMaxCount == 1) {
                NS_RUNTIMEABORT("Not enough memory to even delete objects!");
            }
            aMaxCount /= 2;
        }
    }

    ~SnowWhiteKiller()
    {
        for (uint32_t i = 0; i < mObjects.Length(); ++i) {
            SnowWhiteObject& o = mObjects[i];
            if (!o.mRefCnt->get() && !o.mRefCnt->IsInPurpleBuffer()) {
                mCollector->RemoveObjectFromGraph(o.mPointer);
                o.mRefCnt->stabilizeForDeletion();
                o.mParticipant->DeleteCycleCollectable(o.mPointer);
            }
        }
    }

    void
    Visit(nsPurpleBuffer& aBuffer, nsPurpleBufferEntry* aEntry)
    {
        MOZ_ASSERT(aEntry->mObject, "Null object in purple buffer");
        if (!aEntry->mRefCnt->get()) {
            void *o = aEntry->mObject;
            nsCycleCollectionParticipant *cp = aEntry->mParticipant;
            CanonicalizeParticipant(&o, &cp);
            SnowWhiteObject swo = { o, cp, aEntry->mRefCnt };
            if (mObjects.AppendElement(swo)) {
                aBuffer.Remove(aEntry);
            }
        }
    }

    bool HasSnowWhiteObjects() const
    {
      return mObjects.Length() > 0;
    }

private:
    nsCycleCollector *mCollector;
    FallibleTArray<SnowWhiteObject> mObjects;
};

class RemoveSkippableVisitor : public SnowWhiteKiller
{
public:
    RemoveSkippableVisitor(nsCycleCollector* aCollector,
                           uint32_t aMaxCount, bool aRemoveChildlessNodes,
                           bool aAsyncSnowWhiteFreeing,
                           CC_ForgetSkippableCallback aCb)
        : SnowWhiteKiller(aCollector, aAsyncSnowWhiteFreeing ? 0 : aMaxCount),
          mRemoveChildlessNodes(aRemoveChildlessNodes),
          mAsyncSnowWhiteFreeing(aAsyncSnowWhiteFreeing),
          mDispatchedDeferredDeletion(false),
          mCallback(aCb)
    {}

    ~RemoveSkippableVisitor()
    {
        // Note, we must call the callback before SnowWhiteKiller calls
        // DeleteCycleCollectable!
        if (mCallback) {
            mCallback();
        }
        if (HasSnowWhiteObjects()) {
            // Effectively a continuation.
            nsCycleCollector_dispatchDeferredDeletion(true);
        }
    }

    void
    Visit(nsPurpleBuffer &aBuffer, nsPurpleBufferEntry *aEntry)
    {
        MOZ_ASSERT(aEntry->mObject, "null mObject in purple buffer");
        if (!aEntry->mRefCnt->get()) {
            if (!mAsyncSnowWhiteFreeing) {
                SnowWhiteKiller::Visit(aBuffer, aEntry);
            } else if (!mDispatchedDeferredDeletion) {
                mDispatchedDeferredDeletion = true;
                nsCycleCollector_dispatchDeferredDeletion(false);
            }
            return;
        }
        void *o = aEntry->mObject;
        nsCycleCollectionParticipant *cp = aEntry->mParticipant;
        CanonicalizeParticipant(&o, &cp);
        if (aEntry->mRefCnt->IsPurple() && !cp->CanSkip(o, false) &&
            (!mRemoveChildlessNodes || MayHaveChild(o, cp))) {
            return;
        }
        aBuffer.Remove(aEntry);
    }

private:
    bool mRemoveChildlessNodes;
    bool mAsyncSnowWhiteFreeing;
    bool mDispatchedDeferredDeletion;
    CC_ForgetSkippableCallback mCallback;
};

void
nsPurpleBuffer::RemoveSkippable(nsCycleCollector* aCollector,
                                bool aRemoveChildlessNodes,
                                bool aAsyncSnowWhiteFreeing,
                                CC_ForgetSkippableCallback aCb)
{
    RemoveSkippableVisitor visitor(aCollector, Count(), aRemoveChildlessNodes,
                                   aAsyncSnowWhiteFreeing, aCb);
    VisitEntries(visitor);
}

bool
nsCycleCollector::FreeSnowWhite(bool aUntilNoSWInPurpleBuffer)
{
    CheckThreadSafety();

    bool hadSnowWhiteObjects = false;
    do {
        SnowWhiteKiller visitor(this, mPurpleBuf.Count());
        mPurpleBuf.VisitEntries(visitor);
        hadSnowWhiteObjects = hadSnowWhiteObjects ||
                              visitor.HasSnowWhiteObjects();
        if (!visitor.HasSnowWhiteObjects()) {
            break;
        }
    } while (aUntilNoSWInPurpleBuffer);
    return hadSnowWhiteObjects;
}

void
nsCycleCollector::ForgetSkippable(bool aRemoveChildlessNodes,
                                  bool aAsyncSnowWhiteFreeing)
{
    CheckThreadSafety();
    if (mJSRuntime) {
        mJSRuntime->PrepareForForgetSkippable();
    }
    MOZ_ASSERT(!mScanInProgress, "Don't forget skippable or free snow-white while scan is in progress.");
    mPurpleBuf.RemoveSkippable(this, aRemoveChildlessNodes,
                               aAsyncSnowWhiteFreeing, mForgetSkippableCB);
}

MOZ_NEVER_INLINE void
nsCycleCollector::MarkRoots(SliceBudget &aBudget)
{
    const intptr_t kNumNodesBetweenTimeChecks = 1000;
    const intptr_t kStep = SliceBudget::CounterReset / kNumNodesBetweenTimeChecks;

    TimeLog timeLog;
    AutoRestore<bool> ar(mScanInProgress);
    MOZ_ASSERT(!mScanInProgress);
    mScanInProgress = true;
    MOZ_ASSERT(mIncrementalPhase == GraphBuildingPhase);
    MOZ_ASSERT(mCurrNode);

    while (!aBudget.isOverBudget() && !mCurrNode->IsDone()) {
        PtrInfo *pi = mCurrNode->GetNext();
        CC_AbortIfNull(pi);
        // We need to call the builder's Traverse() method on deleted nodes, to
        // set their firstChild() that may be read by a prior non-deleted
        // neighbor.
        mBuilder->Traverse(pi);
        if (mCurrNode->AtBlockEnd()) {
            mBuilder->SetLastChild();
        }
        aBudget.step(kStep);
    }

    if (!mCurrNode->IsDone()) {
        timeLog.Checkpoint("MarkRoots()");
        return;
    }

    if (mGraph.mRootCount > 0) {
        mBuilder->SetLastChild();
    }

    if (mBuilder->RanOutOfMemory()) {
        MOZ_ASSERT(false, "Ran out of memory while building cycle collector graph");
        CC_TELEMETRY(_OOM, true);
    }

    mBuilder = nullptr;
    mCurrNode = nullptr;
    mIncrementalPhase = ScanAndCollectWhitePhase;
    timeLog.Checkpoint("MarkRoots()");
}


////////////////////////////////////////////////////////////////////////
// Bacon & Rajan's |ScanRoots| routine.
////////////////////////////////////////////////////////////////////////


struct ScanBlackVisitor
{
    ScanBlackVisitor(uint32_t &aWhiteNodeCount, bool &aFailed)
        : mWhiteNodeCount(aWhiteNodeCount), mFailed(aFailed)
    {
    }

    bool ShouldVisitNode(PtrInfo const *pi)
    {
        return pi->mColor != black;
    }

    MOZ_NEVER_INLINE void VisitNode(PtrInfo *pi)
    {
        if (pi->mColor == white)
            --mWhiteNodeCount;
        pi->mColor = black;
    }

    void Failed()
    {
        mFailed = true;
    }

private:
    uint32_t &mWhiteNodeCount;
    bool &mFailed;
};


struct scanVisitor
{
    scanVisitor(uint32_t &aWhiteNodeCount, bool &aFailed)
        : mWhiteNodeCount(aWhiteNodeCount), mFailed(aFailed)
    {
    }

    bool ShouldVisitNode(PtrInfo const *pi)
    {
        return pi->mColor == grey;
    }

    MOZ_NEVER_INLINE void VisitNode(PtrInfo *pi)
    {
        if (pi->mInternalRefs > pi->mRefCount && pi->mRefCount > 0)
            Fault("traversed refs exceed refcount", pi);

        if (pi->mInternalRefs == pi->mRefCount || pi->mRefCount == 0) {
            pi->mColor = white;
            ++mWhiteNodeCount;
        } else {
            GraphWalker<ScanBlackVisitor>(ScanBlackVisitor(mWhiteNodeCount, mFailed)).Walk(pi);
            MOZ_ASSERT(pi->mColor == black,
                       "Why didn't ScanBlackVisitor make pi black?");
        }
    }

    void Failed() {
        mFailed = true;
    }

private:
    uint32_t &mWhiteNodeCount;
    bool &mFailed;
};

// Iterate over the WeakMaps.  If we mark anything while iterating
// over the WeakMaps, we must iterate over all of the WeakMaps again.
void
nsCycleCollector::ScanWeakMaps()
{
    bool anyChanged;
    bool failed = false;
    do {
        anyChanged = false;
        for (uint32_t i = 0; i < mGraph.mWeakMaps.Length(); i++) {
            WeakMapping *wm = &mGraph.mWeakMaps[i];

            // If any of these are null, the original object was marked black.
            uint32_t mColor = wm->mMap ? wm->mMap->mColor : black;
            uint32_t kColor = wm->mKey ? wm->mKey->mColor : black;
            uint32_t kdColor = wm->mKeyDelegate ? wm->mKeyDelegate->mColor : black;
            uint32_t vColor = wm->mVal ? wm->mVal->mColor : black;

            // All non-null weak mapping maps, keys and values are
            // roots (in the sense of WalkFromRoots) in the cycle
            // collector graph, and thus should have been colored
            // either black or white in ScanRoots().
            MOZ_ASSERT(mColor != grey, "Uncolored weak map");
            MOZ_ASSERT(kColor != grey, "Uncolored weak map key");
            MOZ_ASSERT(kdColor != grey, "Uncolored weak map key delegate");
            MOZ_ASSERT(vColor != grey, "Uncolored weak map value");

            if (mColor == black && kColor != black && kdColor == black) {
                GraphWalker<ScanBlackVisitor>(ScanBlackVisitor(mWhiteNodeCount, failed)).Walk(wm->mKey);
                anyChanged = true;
            }

            if (mColor == black && kColor == black && vColor != black) {
                GraphWalker<ScanBlackVisitor>(ScanBlackVisitor(mWhiteNodeCount, failed)).Walk(wm->mVal);
                anyChanged = true;
            }
        }
    } while (anyChanged);

    if (failed) {
        MOZ_ASSERT(false, "Ran out of memory in ScanWeakMaps");
        CC_TELEMETRY(_OOM, true);
    }
}

void
nsCycleCollector::ScanRoots()
{
    TimeLog timeLog;
    AutoRestore<bool> ar(mScanInProgress);
    MOZ_ASSERT(!mScanInProgress);
    mScanInProgress = true;
    mWhiteNodeCount = 0;
    MOZ_ASSERT(mIncrementalPhase == ScanAndCollectWhitePhase);

    // On the assumption that most nodes will be black, it's
    // probably faster to use a GraphWalker than a
    // NodePool::Enumerator.
    bool failed = false;
    GraphWalker<scanVisitor>(scanVisitor(mWhiteNodeCount, failed)).WalkFromRoots(mGraph);

    if (failed) {
        NS_ASSERTION(false, "Ran out of memory in ScanRoots");
        CC_TELEMETRY(_OOM, true);
    }

    ScanWeakMaps();

    if (mListener) {
        mListener->BeginResults();

        NodePool::Enumerator etor(mGraph.mNodes);
        while (!etor.IsDone()) {
            PtrInfo *pi = etor.GetNext();
            if (!pi->mParticipant) {
                continue;
            }
            switch (pi->mColor) {
            case black:
                if (pi->mRefCount > 0 && pi->mRefCount < UINT32_MAX &&
                    pi->mInternalRefs != pi->mRefCount) {
                    mListener->DescribeRoot((uint64_t)pi->mPointer,
                                            pi->mInternalRefs);
                }
                break;
            case white:
                mListener->DescribeGarbage((uint64_t)pi->mPointer);
                break;
            case grey:
                // With incremental CC, we can end up with a grey object after
                // scanning if it is only reachable from an object that gets freed.
                break;
            }
        }

        mListener->End();
        mListener = nullptr;
    }

    timeLog.Checkpoint("ScanRoots()");
}


////////////////////////////////////////////////////////////////////////
// Bacon & Rajan's |CollectWhite| routine, somewhat modified.
////////////////////////////////////////////////////////////////////////

bool
nsCycleCollector::CollectWhite()
{
    // Explanation of "somewhat modified": we have no way to collect the
    // set of whites "all at once", we have to ask each of them to drop
    // their outgoing links and assume this will cause the garbage cycle
    // to *mostly* self-destruct (except for the reference we continue
    // to hold).
    //
    // To do this "safely" we must make sure that the white nodes we're
    // operating on are stable for the duration of our operation. So we
    // make 3 sets of calls to language runtimes:
    //
    //   - Root(whites), which should pin the whites in memory.
    //   - Unlink(whites), which drops outgoing links on each white.
    //   - Unroot(whites), which returns the whites to normal GC.

    TimeLog timeLog;
    nsAutoTArray<PtrInfo*, 4000> whiteNodes;

    MOZ_ASSERT(mIncrementalPhase == ScanAndCollectWhitePhase);

    whiteNodes.SetCapacity(mWhiteNodeCount);
    uint32_t numWhiteGCed = 0;

    NodePool::Enumerator etor(mGraph.mNodes);
    while (!etor.IsDone())
    {
        PtrInfo *pinfo = etor.GetNext();
        if (pinfo->mColor == white && pinfo->mParticipant) {
            whiteNodes.AppendElement(pinfo);
            pinfo->mParticipant->Root(pinfo->mPointer);
            if (pinfo->mRefCount == 0) {
                // only JS objects have a refcount of 0
                ++numWhiteGCed;
            }
        }
    }

    uint32_t count = whiteNodes.Length();
    MOZ_ASSERT(numWhiteGCed <= count,
               "More freed GCed nodes than total freed nodes.");
    mResults.mFreedRefCounted += count - numWhiteGCed;
    mResults.mFreedGCed += numWhiteGCed;

    timeLog.Checkpoint("CollectWhite::Root");

    if (mBeforeUnlinkCB) {
        mBeforeUnlinkCB();
        timeLog.Checkpoint("CollectWhite::BeforeUnlinkCB");
    }

    for (uint32_t i = 0; i < count; ++i) {
        PtrInfo *pinfo = whiteNodes.ElementAt(i);
        MOZ_ASSERT(pinfo->mParticipant, "Unlink shouldn't see objects removed from graph.");
        pinfo->mParticipant->Unlink(pinfo->mPointer);
#ifdef DEBUG
        if (mJSRuntime) {
            mJSRuntime->AssertNoObjectsToTrace(pinfo->mPointer);
        }
#endif
    }
    timeLog.Checkpoint("CollectWhite::Unlink");

    for (uint32_t i = 0; i < count; ++i) {
        PtrInfo *pinfo = whiteNodes.ElementAt(i);
        MOZ_ASSERT(pinfo->mParticipant, "Unroot shouldn't see objects removed from graph.");
        pinfo->mParticipant->Unroot(pinfo->mPointer);
    }
    timeLog.Checkpoint("CollectWhite::Unroot");

    nsCycleCollector_dispatchDeferredDeletion(false);
    mIncrementalPhase = CleanupPhase;

    return count > 0;
}


////////////////////////
// Memory reporting
////////////////////////

MOZ_DEFINE_MALLOC_SIZE_OF(CycleCollectorMallocSizeOf)

NS_IMETHODIMP
nsCycleCollector::CollectReports(nsIHandleReportCallback* aHandleReport,
                                 nsISupports* aData)
{
    size_t objectSize, graphNodesSize, graphEdgesSize, weakMapsSize,
           purpleBufferSize;
    SizeOfIncludingThis(CycleCollectorMallocSizeOf,
                        &objectSize,
                        &graphNodesSize, &graphEdgesSize,
                        &weakMapsSize,
                        &purpleBufferSize);

#define REPORT(_path, _amount, _desc)                                     \
    do {                                                                  \
        size_t amount = _amount;  /* evaluate |_amount| only once */      \
        if (amount > 0) {                                                 \
            nsresult rv;                                                  \
            rv = aHandleReport->Callback(EmptyCString(),                  \
                                         NS_LITERAL_CSTRING(_path),       \
                                         KIND_HEAP, UNITS_BYTES, _amount, \
                                         NS_LITERAL_CSTRING(_desc),       \
                                         aData);                          \
            if (NS_WARN_IF(NS_FAILED(rv)))                                \
                return rv;                                                \
        }                                                                 \
    } while (0)

    REPORT("explicit/cycle-collector/collector-object", objectSize,
           "Memory used for the cycle collector object itself.");

    REPORT("explicit/cycle-collector/graph-nodes", graphNodesSize,
           "Memory used for the nodes of the cycle collector's graph. "
           "This should be zero when the collector is idle.");

    REPORT("explicit/cycle-collector/graph-edges", graphEdgesSize,
           "Memory used for the edges of the cycle collector's graph. "
           "This should be zero when the collector is idle.");

    REPORT("explicit/cycle-collector/weak-maps", weakMapsSize,
           "Memory used for the representation of weak maps in the "
           "cycle collector's graph. "
           "This should be zero when the collector is idle.");

    REPORT("explicit/cycle-collector/purple-buffer", purpleBufferSize,
           "Memory used for the cycle collector's purple buffer.");

#undef REPORT

    return NS_OK;
};


////////////////////////////////////////////////////////////////////////
// Collector implementation
////////////////////////////////////////////////////////////////////////

nsCycleCollector::nsCycleCollector() :
    mActivelyCollecting(false),
    mScanInProgress(false),
    mJSRuntime(nullptr),
    mIncrementalPhase(IdlePhase),
    mThread(NS_GetCurrentThread()),
    mWhiteNodeCount(0),
    mBeforeUnlinkCB(nullptr),
    mForgetSkippableCB(nullptr),
    mUnmergedNeeded(0),
    mMergedInARow(0)
{
}

nsCycleCollector::~nsCycleCollector()
{
    UnregisterWeakMemoryReporter(this);
}

void
nsCycleCollector::RegisterJSRuntime(CycleCollectedJSRuntime *aJSRuntime)
{
    if (mJSRuntime)
        Fault("multiple registrations of cycle collector JS runtime", aJSRuntime);

    mJSRuntime = aJSRuntime;

    // We can't register as a reporter in nsCycleCollector() because that runs
    // before the memory reporter manager is initialized.  So we do it here
    // instead.
    static bool registered = false;
    if (!registered) {
        RegisterWeakMemoryReporter(this);
        registered = true;
    }
}

void
nsCycleCollector::ForgetJSRuntime()
{
    if (!mJSRuntime)
        Fault("forgetting non-registered cycle collector JS runtime");

    mJSRuntime = nullptr;
}

#ifdef DEBUG
static bool
HasParticipant(void *aPtr, nsCycleCollectionParticipant *aParti)
{
    if (aParti) {
        return true;
    }

    nsXPCOMCycleCollectionParticipant *xcp;
    ToParticipant(static_cast<nsISupports*>(aPtr), &xcp);
    return xcp != nullptr;
}
#endif

MOZ_ALWAYS_INLINE void
nsCycleCollector::Suspect(void *aPtr, nsCycleCollectionParticipant *aParti,
                          nsCycleCollectingAutoRefCnt *aRefCnt)
{
    CheckThreadSafety();

    // Re-entering ::Suspect during collection used to be a fault, but
    // we are canonicalizing nsISupports pointers using QI, so we will
    // see some spurious refcount traffic here.

    if (MOZ_UNLIKELY(mScanInProgress)) {
        return;
    }

    MOZ_ASSERT(aPtr, "Don't suspect null pointers");

    MOZ_ASSERT(HasParticipant(aPtr, aParti),
               "Suspected nsISupports pointer must QI to nsXPCOMCycleCollectionParticipant");

    mPurpleBuf.Put(aPtr, aParti, aRefCnt);
}

void
nsCycleCollector::CheckThreadSafety()
{
#ifdef DEBUG
    nsIThread* currentThread = NS_GetCurrentThread();
    // XXXkhuey we can be called so late in shutdown that NS_GetCurrentThread
    // returns null (after the thread manager has shut down)
    MOZ_ASSERT(mThread == currentThread || !currentThread);
#endif
}

// The cycle collector uses the mark bitmap to discover what JS objects
// were reachable only from XPConnect roots that might participate in
// cycles. We ask the JS runtime whether we need to force a GC before
// this CC. It returns true on startup (before the mark bits have been set),
// and also when UnmarkGray has run out of stack.  We also force GCs on shut
// down to collect cycles involving both DOM and JS.
void
nsCycleCollector::FixGrayBits(bool aForceGC)
{
    CheckThreadSafety();

    if (!mJSRuntime)
        return;

    if (!aForceGC) {
        mJSRuntime->FixWeakMappingGrayBits();

        bool needGC = mJSRuntime->NeedCollect();
        // Only do a telemetry ping for non-shutdown CCs.
        CC_TELEMETRY(_NEED_GC, needGC);
        if (!needGC)
            return;
        mResults.mForcedGC = true;
    }

    TimeLog timeLog;
    mJSRuntime->Collect(aForceGC ? JS::gcreason::SHUTDOWN_CC : JS::gcreason::CC_FORCED);
    timeLog.Checkpoint("GC()");
}

void
nsCycleCollector::CleanupAfterCollection()
{
    MOZ_ASSERT(mIncrementalPhase == CleanupPhase);
    mGraph.Clear();

#ifdef XP_OS2
    // Now that the cycle collector has freed some memory, we can try to
    // force the C library to give back as much memory to the system as
    // possible.
    _heapmin();
#endif

    uint32_t interval = (uint32_t) ((TimeStamp::Now() - mCollectionStart).ToMilliseconds());
#ifdef COLLECT_TIME_DEBUG
    printf("cc: total cycle collector time was %ums\n", interval);
    printf("cc: visited %u ref counted and %u GCed objects, freed %d ref counted and %d GCed objects.\n",
           mResults.mVisitedRefCounted, mResults.mVisitedGCed,
           mResults.mFreedRefCounted, mResults.mFreedGCed);
    printf("cc: \n");
#endif
    CC_TELEMETRY( , interval);
    CC_TELEMETRY(_VISITED_REF_COUNTED, mResults.mVisitedRefCounted);
    CC_TELEMETRY(_VISITED_GCED, mResults.mVisitedGCed);
    CC_TELEMETRY(_COLLECTED, mWhiteNodeCount);

    if (mJSRuntime) {
        mJSRuntime->EndCycleCollectionCallback(mResults);
    }
    mIncrementalPhase = IdlePhase;
}

void
nsCycleCollector::ShutdownCollect()
{
    SliceBudget unlimitedBudget;
    uint32_t i;
    for (i = 0; i < DEFAULT_SHUTDOWN_COLLECTIONS; ++i) {
        if (!Collect(ShutdownCC, unlimitedBudget, nullptr)) {
            break;
        }
    }
}

static void
PrintPhase(const char *aPhase)
{
#ifdef DEBUG_PHASES
    printf("cc: begin %s on %s\n", aPhase,
           NS_IsMainThread() ? "mainthread" : "worker");
#endif
}

bool
nsCycleCollector::Collect(ccType aCCType,
                          SliceBudget &aBudget,
                          nsICycleCollectorListener *aManualListener)
{
    CheckThreadSafety();

    // This can legitimately happen in a few cases. See bug 383651.
    if (mActivelyCollecting) {
        return false;
    }
    mActivelyCollecting = true;

    bool startedIdle = (mIncrementalPhase == IdlePhase);
    bool collectedAny = false;

    // If the CC started idle, it will call BeginCollection, which
    // will do FreeSnowWhite, so it doesn't need to be done here.
    if (!startedIdle) {
        FreeSnowWhite(true);
    }

    bool finished = false;
    do {
        switch (mIncrementalPhase) {
        case IdlePhase:
            PrintPhase("BeginCollection");
            BeginCollection(aCCType, aManualListener);
            break;
        case GraphBuildingPhase:
            PrintPhase("MarkRoots");
            MarkRoots(aBudget);
            break;
        case ScanAndCollectWhitePhase:
            // We do ScanRoots and CollectWhite in a single slice to ensure
            // that we won't unlink a live object if a weak reference is
            // promoted to a strong reference after ScanRoots has finished.
            // See bug 926533.
            PrintPhase("ScanRoots");
            ScanRoots();
            PrintPhase("CollectWhite");
            collectedAny = CollectWhite();
            break;
        case CleanupPhase:
            PrintPhase("CleanupAfterCollection");
            CleanupAfterCollection();
            finished = true;
            break;
        }
    } while (!aBudget.checkOverBudget() && !finished);

    mActivelyCollecting = false;

    if (aCCType != ScheduledCC && !startedIdle) {
        // We were in the middle of an incremental CC (using its own listener).
        // Somebody has forced a CC, so after having finished out the current CC,
        // run the CC again using the new listener.
        MOZ_ASSERT(mIncrementalPhase == IdlePhase);
        if (Collect(aCCType, aBudget, aManualListener)) {
            collectedAny = true;
        }
    }

    MOZ_ASSERT_IF(aCCType != ScheduledCC, mIncrementalPhase == IdlePhase);

    return collectedAny;
}

// Any JS objects we have in the graph could die when we GC, but we
// don't want to abandon the current CC, because the graph contains
// information about purple roots. So we synchronously finish off
// the current CC.
void nsCycleCollector::PrepareForGarbageCollection()
{
    if (mIncrementalPhase == IdlePhase) {
        MOZ_ASSERT(mGraph.IsEmpty(), "Non-empty graph when idle");
        MOZ_ASSERT(!mBuilder, "Non-null builder when idle");
        return;
    }

    SliceBudget unlimitedBudget;
    PrintPhase("PrepareForGarbageCollection");
    Collect(ScheduledCC, unlimitedBudget, nullptr);
    MOZ_ASSERT(mIncrementalPhase == IdlePhase);
}

// Don't merge too many times in a row, and do at least a minimum
// number of unmerged CCs in a row.
static const uint32_t kMinConsecutiveUnmerged = 3;
static const uint32_t kMaxConsecutiveMerged = 3;

bool
nsCycleCollector::ShouldMergeZones(ccType aCCType)
{
    if (!mJSRuntime) {
        return false;
    }

    MOZ_ASSERT(mUnmergedNeeded <= kMinConsecutiveUnmerged);
    MOZ_ASSERT(mMergedInARow <= kMaxConsecutiveMerged);

    if (mMergedInARow == kMaxConsecutiveMerged) {
        MOZ_ASSERT(mUnmergedNeeded == 0);
        mUnmergedNeeded = kMinConsecutiveUnmerged;
    }

    if (mUnmergedNeeded > 0) {
        mUnmergedNeeded--;
        mMergedInARow = 0;
        return false;
    }

    if (aCCType == ScheduledCC && mJSRuntime->UsefulToMergeZones()) {
        mMergedInARow++;
        return true;
    } else {
        mMergedInARow = 0;
        return false;
    }
}

void
nsCycleCollector::BeginCollection(ccType aCCType,
                                  nsICycleCollectorListener *aManualListener)
{
    TimeLog timeLog;
    MOZ_ASSERT(mIncrementalPhase == IdlePhase);

    mCollectionStart = TimeStamp::Now();

    if (mJSRuntime) {
        mJSRuntime->BeginCycleCollectionCallback();
        timeLog.Checkpoint("BeginCycleCollectionCallback()");
    }

    bool isShutdown = (aCCType == ShutdownCC);

    // Set up the listener for this CC.
    MOZ_ASSERT_IF(isShutdown, !aManualListener);
    MOZ_ASSERT(!mListener, "Forgot to clear a previous listener?");
    mListener = aManualListener;
    aManualListener = nullptr;
    if (!mListener) {
        if (mParams.mLogAll || (isShutdown && mParams.mLogShutdown)) {
            nsRefPtr<nsCycleCollectorLogger> logger = new nsCycleCollectorLogger();
            if (isShutdown && mParams.mAllTracesAtShutdown) {
                logger->SetAllTraces();
            }
            mListener = logger.forget();
        }
    }

    bool forceGC = isShutdown;
    if (!forceGC && mListener) {
        // On a WantAllTraces CC, force a synchronous global GC to prevent
        // hijinks from ForgetSkippable and compartmental GCs.
        mListener->GetWantAllTraces(&forceGC);
    }
    FixGrayBits(forceGC);

    FreeSnowWhite(true);

    if (mListener && NS_FAILED(mListener->Begin())) {
        mListener = nullptr;
    }

    // Set up the data structures for building the graph.
    mGraph.Init();
    mResults.Init();
    bool mergeZones = ShouldMergeZones(aCCType);
    mResults.mMergedZones = mergeZones;

    MOZ_ASSERT(!mBuilder, "Forgot to clear mBuilder");
    mBuilder = new GCGraphBuilder(mGraph, mResults, mJSRuntime, mListener, mergeZones);

    if (mJSRuntime) {
        mJSRuntime->BeginCycleCollection(*mBuilder);
        timeLog.Checkpoint("mJSRuntime->BeginCycleCollection()");
    }

    AutoRestore<bool> ar(mScanInProgress);
    MOZ_ASSERT(!mScanInProgress);
    mScanInProgress = true;
    mPurpleBuf.SelectPointers(*mBuilder);
    timeLog.Checkpoint("SelectPointers()");

    // We've finished adding roots, and everything in the graph is a root.
    mGraph.mRootCount = mGraph.MapCount();

    mCurrNode = new NodePool::Enumerator(mGraph.mNodes);
    mIncrementalPhase = GraphBuildingPhase;
}

uint32_t
nsCycleCollector::SuspectedCount()
{
    CheckThreadSafety();
    return mPurpleBuf.Count();
}

void
nsCycleCollector::Shutdown()
{
    CheckThreadSafety();

    // Always delete snow white objects.
    FreeSnowWhite(true);

#ifndef DEBUG
    if (PR_GetEnv("XPCOM_CC_RUN_DURING_SHUTDOWN"))
#endif
    {
        ShutdownCollect();
    }
}

void
nsCycleCollector::RemoveObjectFromGraph(void *aObj)
{
    if (mIncrementalPhase == IdlePhase) {
        return;
    }

    if (PtrInfo *pinfo = mGraph.FindNode(aObj)) {
        mGraph.RemoveNodeFromMap(aObj);

        pinfo->mPointer = nullptr;
        pinfo->mParticipant = nullptr;
    }
}

void
nsCycleCollector::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                      size_t *aObjectSize,
                                      size_t *aGraphNodesSize,
                                      size_t *aGraphEdgesSize,
                                      size_t *aWeakMapsSize,
                                      size_t *aPurpleBufferSize) const
{
    *aObjectSize = aMallocSizeOf(this);

    mGraph.SizeOfExcludingThis(aMallocSizeOf, aGraphNodesSize, aGraphEdgesSize,
                               aWeakMapsSize);

    *aPurpleBufferSize = mPurpleBuf.SizeOfExcludingThis(aMallocSizeOf);

    // These fields are deliberately not measured:
    // - mJSRuntime: because it's non-owning and measured by JS reporters.
    // - mParams: because it only contains scalars.
}

////////////////////////////////////////////////////////////////////////
// Module public API (exported in nsCycleCollector.h)
// Just functions that redirect into the singleton, once it's built.
////////////////////////////////////////////////////////////////////////

void
nsCycleCollector_registerJSRuntime(CycleCollectedJSRuntime *rt)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);
    // But we shouldn't already have a runtime.
    MOZ_ASSERT(!data->mRuntime);

    data->mRuntime = rt;
    data->mCollector->RegisterJSRuntime(rt);
}

void
nsCycleCollector_forgetJSRuntime()
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    // And we shouldn't have already forgotten our runtime.
    MOZ_ASSERT(data->mRuntime);

    // But it may have shutdown already.
    if (data->mCollector) {
        data->mCollector->ForgetJSRuntime();
        data->mRuntime = nullptr;
    } else {
        data->mRuntime = nullptr;
        delete data;
        sCollectorData.set(nullptr);
    }
}

/* static */ CycleCollectedJSRuntime*
CycleCollectedJSRuntime::Get()
{
    CollectorData* data = sCollectorData.get();
    if (data) {
        return data->mRuntime;
    }
    return nullptr;
}


namespace mozilla {
namespace cyclecollector {

void
HoldJSObjectsImpl(void* aHolder, nsScriptObjectTracer* aTracer)
{
    CollectorData* data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);
    // And we should have a runtime.
    MOZ_ASSERT(data->mRuntime);

    data->mRuntime->AddJSHolder(aHolder, aTracer);
}

void
HoldJSObjectsImpl(nsISupports* aHolder)
{
    nsXPCOMCycleCollectionParticipant* participant;
    CallQueryInterface(aHolder, &participant);
    MOZ_ASSERT(participant, "Failed to QI to nsXPCOMCycleCollectionParticipant!");
    MOZ_ASSERT(participant->CheckForRightISupports(aHolder),
               "The result of QIing a JS holder should be the same as ToSupports");

    HoldJSObjectsImpl(aHolder, participant);
}

void
DropJSObjectsImpl(void* aHolder)
{
    CollectorData* data = sCollectorData.get();

    // We should have started the cycle collector by now, and not completely
    // shut down.
    MOZ_ASSERT(data);
    // And we should have a runtime.
    MOZ_ASSERT(data->mRuntime);

    data->mRuntime->RemoveJSHolder(aHolder);
}

void
DropJSObjectsImpl(nsISupports* aHolder)
{
#ifdef DEBUG
    nsXPCOMCycleCollectionParticipant* participant;
    CallQueryInterface(aHolder, &participant);
    MOZ_ASSERT(participant, "Failed to QI to nsXPCOMCycleCollectionParticipant!");
    MOZ_ASSERT(participant->CheckForRightISupports(aHolder),
               "The result of QIing a JS holder should be the same as ToSupports");
#endif
    DropJSObjectsImpl(static_cast<void*>(aHolder));
}

#ifdef DEBUG
bool
IsJSHolder(void* aHolder)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now, and not completely
    // shut down.
    MOZ_ASSERT(data);
    // And we should have a runtime.
    MOZ_ASSERT(data->mRuntime);

    return data->mRuntime->IsJSHolder(aHolder);
}
#endif

void
DeferredFinalize(nsISupports* aSupports)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now, and not completely
    // shut down.
    MOZ_ASSERT(data);
    // And we should have a runtime.
    MOZ_ASSERT(data->mRuntime);

    data->mRuntime->DeferredFinalize(aSupports);
}

void
DeferredFinalize(DeferredFinalizeAppendFunction aAppendFunc,
                 DeferredFinalizeFunction aFunc,
                 void* aThing)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now, and not completely
    // shut down.
    MOZ_ASSERT(data);
    // And we should have a runtime.
    MOZ_ASSERT(data->mRuntime);

    data->mRuntime->DeferredFinalize(aAppendFunc, aFunc, aThing);
}

} // namespace cyclecollector
} // namespace mozilla


MOZ_NEVER_INLINE static void
SuspectAfterShutdown(void* n, nsCycleCollectionParticipant* cp,
                     nsCycleCollectingAutoRefCnt* aRefCnt,
                     bool* aShouldDelete)
{
    if (aRefCnt->get() == 0) {
        if (!aShouldDelete) {
            // The CC is shut down, so we can't be in the middle of an ICC.
            CanonicalizeParticipant(&n, &cp);
            aRefCnt->stabilizeForDeletion();
            cp->DeleteCycleCollectable(n);
        } else {
            *aShouldDelete = true;
        }
    } else {
        // Make sure we'll get called again.
        aRefCnt->RemoveFromPurpleBuffer();
    }
}

void
NS_CycleCollectorSuspect3(void *n, nsCycleCollectionParticipant *cp,
                          nsCycleCollectingAutoRefCnt *aRefCnt,
                          bool* aShouldDelete)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);

    if (MOZ_LIKELY(data->mCollector)) {
        data->mCollector->Suspect(n, cp, aRefCnt);
        return;
    }
    SuspectAfterShutdown(n, cp, aRefCnt, aShouldDelete);
}

uint32_t
nsCycleCollector_suspectedCount()
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);

    if (!data->mCollector) {
        return 0;
    }

    return data->mCollector->SuspectedCount();
}

bool
nsCycleCollector_init()
{
    MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
    MOZ_ASSERT(!sCollectorData.initialized(), "Called twice!?");

    return sCollectorData.init();
}

void
nsCycleCollector_startup()
{
    MOZ_ASSERT(sCollectorData.initialized(),
               "Forgot to call nsCycleCollector_init!");
    if (sCollectorData.get()) {
        MOZ_CRASH();
    }

    CollectorData* data = new CollectorData;
    data->mCollector = new nsCycleCollector();
    data->mRuntime = nullptr;

    sCollectorData.set(data);
}

void
nsCycleCollector_setBeforeUnlinkCallback(CC_BeforeUnlinkCallback aCB)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);

    data->mCollector->SetBeforeUnlinkCallback(aCB);
}

void
nsCycleCollector_setForgetSkippableCallback(CC_ForgetSkippableCallback aCB)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);

    data->mCollector->SetForgetSkippableCallback(aCB);
}

void
nsCycleCollector_forgetSkippable(bool aRemoveChildlessNodes,
                                 bool aAsyncSnowWhiteFreeing)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);

    PROFILER_LABEL("CC", "nsCycleCollector_forgetSkippable");
    TimeLog timeLog;
    data->mCollector->ForgetSkippable(aRemoveChildlessNodes,
                                      aAsyncSnowWhiteFreeing);
    timeLog.Checkpoint("ForgetSkippable()");
}

void
nsCycleCollector_dispatchDeferredDeletion(bool aContinuation)
{
    CollectorData *data = sCollectorData.get();

    if (!data || !data->mRuntime) {
        return;
    }

    data->mRuntime->DispatchDeferredDeletion(aContinuation);
}

bool
nsCycleCollector_doDeferredDeletion()
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);
    MOZ_ASSERT(data->mRuntime);

    return data->mCollector->FreeSnowWhite(false);
}

void
nsCycleCollector_collect(nsICycleCollectorListener *aManualListener)
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);

    PROFILER_LABEL("CC", "nsCycleCollector_collect");
    SliceBudget unlimitedBudget;
    data->mCollector->Collect(ManualCC, unlimitedBudget, aManualListener);
}

void
nsCycleCollector_scheduledCollect()
{
    CollectorData *data = sCollectorData.get();

    // We should have started the cycle collector by now.
    MOZ_ASSERT(data);
    MOZ_ASSERT(data->mCollector);

    PROFILER_LABEL("CC", "nsCycleCollector_scheduledCollect");
    SliceBudget unlimitedBudget;
    data->mCollector->Collect(ScheduledCC, unlimitedBudget, nullptr);
}

void
nsCycleCollector_prepareForGarbageCollection()
{
    CollectorData *data = sCollectorData.get();

    MOZ_ASSERT(data);

    if (!data->mCollector) {
        return;
    }

    data->mCollector->PrepareForGarbageCollection();
}

void
nsCycleCollector_shutdown()
{
    CollectorData *data = sCollectorData.get();

    if (data) {
        MOZ_ASSERT(data->mCollector);
        PROFILER_LABEL("CC", "nsCycleCollector_shutdown");
        data->mCollector->Shutdown();
        data->mCollector = nullptr;
        if (!data->mRuntime) {
          delete data;
          sCollectorData.set(nullptr);
        }
    }
}