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Bug 1392881 - Merge StaticAtom and DynamicAtom. r=froydnj.

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There's no reason for them to be separate, and we can use the |kind| field to
distinguish the two kinds when necessary.

This lets us remove the duplication of ScriptableToString(), ToUTF8String(),
and ScriptableEquals().

It also lets us use |Atom*| pointers instead of |nsIAtom*| pointers in various
places within nsAtomTable.cpp, which de-virtualizes various calls and removes
the need for some static_casts.

--HG--
extra : rebase_source : 2f9183323446e353f8cc5dcedf57d9dc9a38f0a7
This commit is contained in:
Nicholas Nethercote 2017-08-24 11:10:04 +10:00
parent 821308e4d1
commit 0a0c70a23a
1 changed files with 136 additions and 163 deletions
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299
xpcom/ds/nsAtomTable.cpp
View File

@ -28,20 +28,20 @@
// There are two kinds of atoms handled by this module.
//
// - DynamicAtom: the atom itself is heap allocated, as is the nsStringBuffer it
// points to. |gAtomTable| holds weak references to them DynamicAtoms. When
// the refcount of a DynamicAtom drops to zero, we increment a static counter.
// When that counter reaches a certain threshold, we iterate over the atom
// table, removing and deleting DynamicAtoms with refcount zero. This allows
// - Dynamic: the Atom itself is heap allocated, as is the nsStringBuffer it
// points to. |gAtomTable| holds weak references to dynamic Atoms. When the
// refcount of a dynamic Atom drops to zero, we increment a static counter.
// When that counter reaches a certain threshold, we iterate over the Atom
// table, removing and deleting dynamic Atoms with refcount zero. This allows
// us to avoid acquiring the atom table lock during normal refcounting.
//
// - StaticAtom: the atom itself is heap allocated, but it points to a static
// nsStringBuffer. |gAtomTable| effectively owns StaticAtoms, because such
// atoms ignore all AddRef/Release calls, which ensures they stay alive until
// - Static: the Atom itself is heap allocated, but it points to a static
// nsStringBuffer. |gAtomTable| effectively owns static Atoms, because such
// Atoms ignore all AddRef/Release calls, which ensures they stay alive until
// |gAtomTable| itself is destroyed whereupon they are explicitly deleted.
//
// Note that gAtomTable is used on multiple threads, and callers must
// acquire gAtomTableLock before touching it.
// Note that gAtomTable is used on multiple threads, and callers must acquire
// gAtomTableLock before touching it.
using namespace mozilla;
@ -69,77 +69,6 @@ class CheckStaticAtomSizes
static Atomic<uint32_t, ReleaseAcquire> gUnusedAtomCount(0);
class DynamicAtom final : public nsIAtom
{
public:
static already_AddRefed<DynamicAtom> Create(const nsAString& aString, uint32_t aHash)
{
// The refcount is appropriately initialized in the constructor.
return dont_AddRef(new DynamicAtom(aString, aHash));
}
static void GCAtomTable();
enum class GCKind {
RegularOperation,
Shutdown,
};
static void GCAtomTableLocked(const MutexAutoLock& aProofOfLock,
GCKind aKind);
private:
DynamicAtom(const nsAString& aString, uint32_t aHash)
: mRefCnt(1)
{
mLength = aString.Length();
SetKind(AtomKind::DynamicAtom);
RefPtr<nsStringBuffer> buf = nsStringBuffer::FromString(aString);
if (buf) {
mString = static_cast<char16_t*>(buf->Data());
} else {
const size_t size = (mLength + 1) * sizeof(char16_t);
buf = nsStringBuffer::Alloc(size);
if (MOZ_UNLIKELY(!buf)) {
// We OOM because atom allocations should be small and it's hard to
// handle them more gracefully in a constructor.
NS_ABORT_OOM(size);
}
mString = static_cast<char16_t*>(buf->Data());
CopyUnicodeTo(aString, 0, mString, mLength);
mString[mLength] = char16_t(0);
}
mHash = aHash;
MOZ_ASSERT(mHash == HashString(mString, mLength));
NS_ASSERTION(mString[mLength] == char16_t(0), "null terminated");
NS_ASSERTION(buf && buf->StorageSize() >= (mLength + 1) * sizeof(char16_t),
"enough storage");
NS_ASSERTION(Equals(aString), "correct data");
// Take ownership of buffer
mozilla::Unused << buf.forget();
}
private:
// We don't need a virtual destructor because we always delete via a
// DynamicAtom* pointer (in GCAtomTable()), not an nsIAtom* pointer.
~DynamicAtom();
public:
NS_DECL_NSIATOM
NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) final;
typedef mozilla::TrueType HasThreadSafeRefCnt;
MozExternalRefCountType DoAddRef();
MozExternalRefCountType DoRelease();
protected:
ThreadSafeAutoRefCnt mRefCnt;
NS_DECL_OWNINGTHREAD
};
#if defined(NS_BUILD_REFCNT_LOGGING)
// nsFakeStringBuffers don't really use the refcounting system, but we
// have to give a coherent series of addrefs and releases to the
@ -173,10 +102,69 @@ private:
UniquePtr<nsTArray<FakeBufferRefcountHelper>> gFakeBuffers;
#endif
class StaticAtom final : public nsIAtom
class Atom final : public nsIAtom
{
public:
StaticAtom(nsStringBuffer* aStringBuffer, uint32_t aLength, uint32_t aHash)
static already_AddRefed<Atom> CreateDynamic(const nsAString& aString,
uint32_t aHash)
{
// The refcount is appropriately initialized in the constructor.
return dont_AddRef(new Atom(aString, aHash));
}
static Atom* CreateStatic(nsStringBuffer* aStringBuffer, uint32_t aLength,
uint32_t aHash)
{
return new Atom(aStringBuffer, aLength, aHash);
}
static void GCAtomTable();
enum class GCKind {
RegularOperation,
Shutdown,
};
static void GCAtomTableLocked(const MutexAutoLock& aProofOfLock,
GCKind aKind);
private:
// This constructor is for dynamic Atoms.
Atom(const nsAString& aString, uint32_t aHash)
: mRefCnt(1)
{
mLength = aString.Length();
SetKind(AtomKind::DynamicAtom);
RefPtr<nsStringBuffer> buf = nsStringBuffer::FromString(aString);
if (buf) {
mString = static_cast<char16_t*>(buf->Data());
} else {
const size_t size = (mLength + 1) * sizeof(char16_t);
buf = nsStringBuffer::Alloc(size);
if (MOZ_UNLIKELY(!buf)) {
// We OOM because atom allocations should be small and it's hard to
// handle them more gracefully in a constructor.
NS_ABORT_OOM(size);
}
mString = static_cast<char16_t*>(buf->Data());
CopyUnicodeTo(aString, 0, mString, mLength);
mString[mLength] = char16_t(0);
}
mHash = aHash;
MOZ_ASSERT(mHash == HashString(mString, mLength));
NS_ASSERTION(mString[mLength] == char16_t(0), "null terminated");
NS_ASSERTION(buf && buf->StorageSize() >= (mLength + 1) * sizeof(char16_t),
"enough storage");
NS_ASSERTION(Equals(aString), "correct data");
// Take ownership of buffer
mozilla::Unused << buf.forget();
}
// This constructor is for static Atoms.
Atom(nsStringBuffer* aStringBuffer, uint32_t aLength, uint32_t aHash)
{
mLength = aLength;
SetKind(AtomKind::StaticAtom);
@ -203,73 +191,65 @@ public:
"correct storage");
}
// We don't need a virtual destructor because we always delete via a
// StaticAtom* pointer (in AtomTableClearEntry()), not an nsIAtom* pointer.
~StaticAtom() {}
public:
// We don't need a virtual destructor because we always delete via an Atom*
// pointer (in AtomTableClearEntry() for static Atoms, and in
// GCAtomTableLocked() for dynamic Atoms), not an nsIAtom* pointer.
~Atom() {
if (IsDynamicAtom()) {
nsStringBuffer::FromData(mString)->Release();
} else {
MOZ_ASSERT(IsStaticAtom());
}
}
NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) final;
NS_DECL_NSIATOM
NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) final;
typedef mozilla::TrueType HasThreadSafeRefCnt;
MozExternalRefCountType DynamicAddRef();
MozExternalRefCountType DynamicRelease();
protected:
ThreadSafeAutoRefCnt mRefCnt;
NS_DECL_OWNINGTHREAD
};
NS_IMPL_QUERY_INTERFACE(StaticAtom, nsIAtom);
NS_IMPL_QUERY_INTERFACE(Atom, nsIAtom);
NS_IMETHODIMP
DynamicAtom::ScriptableToString(nsAString& aBuf)
Atom::ScriptableToString(nsAString& aBuf)
{
nsStringBuffer::FromData(mString)->ToString(mLength, aBuf);
return NS_OK;
}
NS_IMETHODIMP
StaticAtom::ScriptableToString(nsAString& aBuf)
{
nsStringBuffer::FromData(mString)->ToString(mLength, aBuf);
return NS_OK;
}
NS_IMETHODIMP
DynamicAtom::ToUTF8String(nsACString& aBuf)
Atom::ToUTF8String(nsACString& aBuf)
{
CopyUTF16toUTF8(nsDependentString(mString, mLength), aBuf);
return NS_OK;
}
NS_IMETHODIMP
StaticAtom::ToUTF8String(nsACString& aBuf)
{
CopyUTF16toUTF8(nsDependentString(mString, mLength), aBuf);
return NS_OK;
}
NS_IMETHODIMP
DynamicAtom::ScriptableEquals(const nsAString& aString, bool* aResult)
{
*aResult = aString.Equals(nsDependentString(mString, mLength));
return NS_OK;
}
NS_IMETHODIMP
StaticAtom::ScriptableEquals(const nsAString& aString, bool* aResult)
Atom::ScriptableEquals(const nsAString& aString, bool* aResult)
{
*aResult = aString.Equals(nsDependentString(mString, mLength));
return NS_OK;
}
NS_IMETHODIMP_(size_t)
DynamicAtom::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf)
Atom::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf)
{
size_t n = aMallocSizeOf(this);
n += nsStringBuffer::FromData(mString)->SizeOfIncludingThisIfUnshared(
aMallocSizeOf);
return n;
}
NS_IMETHODIMP_(size_t)
StaticAtom::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf)
{
size_t n = aMallocSizeOf(this);
// Don't measure the string buffer pointed to by the StaticAtom because it's
// in static memory.
// String buffers pointed to by static atoms are in static memory, and so
// are not measured here.
if (IsDynamicAtom()) {
n += nsStringBuffer::FromData(mString)->SizeOfIncludingThisIfUnshared(
aMallocSizeOf);
} else {
MOZ_ASSERT(IsStaticAtom());
}
return n;
}
@ -283,7 +263,7 @@ nsIAtom::AddRef()
MOZ_ASSERT(IsStaticAtom());
return 2;
}
return static_cast<DynamicAtom*>(this)->DoAddRef();
return static_cast<Atom*>(this)->DynamicAddRef();
}
NS_IMETHODIMP_(MozExternalRefCountType)
@ -294,7 +274,7 @@ nsIAtom::Release()
MOZ_ASSERT(IsStaticAtom());
return 1;
}
return static_cast<DynamicAtom*>(this)->DoRelease();
return static_cast<Atom*>(this)->DynamicRelease();
}
//----------------------------------------------------------------------
@ -361,10 +341,10 @@ struct AtomTableKey
struct AtomTableEntry : public PLDHashEntryHdr
{
// These references are either to DynamicAtoms, in which case they are
// non-owning, or they are to StaticAtoms, which aren't really refcounted.
// These references are either to dynamic Atoms, in which case they are
// non-owning, or they are to static Atoms, which aren't really refcounted.
// See the comment at the top of this file for more details.
nsIAtom* MOZ_NON_OWNING_REF mAtom;
Atom* MOZ_NON_OWNING_REF mAtom;
};
static PLDHashNumber
@ -394,13 +374,12 @@ static void
AtomTableClearEntry(PLDHashTable* aTable, PLDHashEntryHdr* aEntry)
{
auto entry = static_cast<AtomTableEntry*>(aEntry);
nsIAtom* atom = entry->mAtom;
Atom* atom = entry->mAtom;
if (atom->IsStaticAtom()) {
// This case -- when the entry being cleared holds a StaticAtom -- only
// occurs when gAtomTable is destroyed, whereupon all StaticAtoms within it
// must be explicitly deleted. The cast is required because StaticAtom
// doesn't have a virtual destructor.
delete static_cast<StaticAtom*>(atom);
// This case -- when the entry being cleared holds a static Atom -- only
// occurs when gAtomTable is destroyed, whereupon all static Atoms within it
// must be explicitly deleted.
delete atom;
}
}
@ -421,11 +400,11 @@ static const PLDHashTableOps AtomTableOps = {
//----------------------------------------------------------------------
#define RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE 31
static nsIAtom*
static Atom*
sRecentlyUsedMainThreadAtoms[RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE] = {};
void
DynamicAtom::GCAtomTable()
Atom::GCAtomTable()
{
if (NS_IsMainThread()) {
MutexAutoLock lock(*gAtomTableLock);
@ -434,8 +413,7 @@ DynamicAtom::GCAtomTable()
}
void
DynamicAtom::GCAtomTableLocked(const MutexAutoLock& aProofOfLock,
GCKind aKind)
Atom::GCAtomTableLocked(const MutexAutoLock& aProofOfLock, GCKind aKind)
{
MOZ_ASSERT(NS_IsMainThread());
for (uint32_t i = 0; i < RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE; ++i) {
@ -451,7 +429,7 @@ DynamicAtom::GCAtomTableLocked(const MutexAutoLock& aProofOfLock,
continue;
}
auto atom = static_cast<DynamicAtom*>(entry->mAtom);
Atom* atom = entry->mAtom;
if (atom->mRefCnt == 0) {
i.Remove();
delete atom;
@ -502,11 +480,10 @@ DynamicAtom::GCAtomTableLocked(const MutexAutoLock& aProofOfLock,
gUnusedAtomCount -= removedCount;
}
NS_IMPL_QUERY_INTERFACE(DynamicAtom, nsIAtom)
MozExternalRefCountType
DynamicAtom::DoAddRef()
Atom::DynamicAddRef()
{
MOZ_ASSERT(IsDynamicAtom());
nsrefcnt count = ++mRefCnt;
if (count == 1) {
gUnusedAtomCount--;
@ -523,8 +500,9 @@ static const uint32_t kAtomGCThreshold = 10000;
#endif
MozExternalRefCountType
DynamicAtom::DoRelease()
Atom::DynamicRelease()
{
MOZ_ASSERT(IsDynamicAtom());
MOZ_ASSERT(mRefCnt > 0);
nsrefcnt count = --mRefCnt;
if (count == 0) {
@ -536,11 +514,6 @@ DynamicAtom::DoRelease()
return count;
}
DynamicAtom::~DynamicAtom()
{
nsStringBuffer::FromData(mString)->Release();
}
//----------------------------------------------------------------------
class StaticAtomEntry : public PLDHashEntryHdr
@ -570,9 +543,9 @@ public:
enum { ALLOW_MEMMOVE = true };
// StaticAtoms aren't really refcounted. Because these entries live in a
// Static Atoms aren't really refcounted. Because these entries live in a
// global hashtable, this reference is essentially owning.
StaticAtom* MOZ_OWNING_REF mAtom;
Atom* MOZ_OWNING_REF mAtom;
};
/**
@ -637,7 +610,7 @@ NS_ShutdownAtomTable()
// builds.
{
MutexAutoLock lock(*gAtomTableLock);
DynamicAtom::GCAtomTableLocked(lock, DynamicAtom::GCKind::Shutdown);
Atom::GCAtomTableLocked(lock, Atom::GCKind::Shutdown);
}
#endif
@ -708,7 +681,7 @@ RegisterStaticAtoms(const nsStaticAtom* aAtoms, uint32_t aAtomCount)
GetAtomHashEntry(static_cast<char16_t*>(stringBuffer->Data()),
stringLen, &hash);
nsIAtom* atom = he->mAtom;
Atom* atom = he->mAtom;
if (atom) {
// Disallow creating a dynamic atom, and then later, while the
// dynamic atom is still alive, registering that same atom as a
@ -721,7 +694,7 @@ RegisterStaticAtoms(const nsStaticAtom* aAtoms, uint32_t aAtomCount)
"Static atom registration for %s should be pushed back", name.get());
}
} else {
atom = new StaticAtom(stringBuffer, stringLen, hash);
atom = Atom::CreateStatic(stringBuffer, stringLen, hash);
he->mAtom = atom;
}
*atomp = atom;
@ -730,7 +703,7 @@ RegisterStaticAtoms(const nsStaticAtom* aAtoms, uint32_t aAtomCount)
StaticAtomEntry* entry =
gStaticAtomTable->PutEntry(nsDependentAtomString(atom));
MOZ_ASSERT(atom->IsStaticAtom());
entry->mAtom = static_cast<StaticAtom*>(atom);
entry->mAtom = atom;
}
}
}
@ -761,7 +734,7 @@ NS_Atomize(const nsACString& aUTF8String)
// Actually, now there is, sort of: ForgetSharedBuffer.
nsString str;
CopyUTF8toUTF16(aUTF8String, str);
RefPtr<DynamicAtom> atom = DynamicAtom::Create(str, hash);
RefPtr<Atom> atom = Atom::CreateDynamic(str, hash);
he->mAtom = atom;
@ -789,7 +762,7 @@ NS_Atomize(const nsAString& aUTF16String)
return atom.forget();
}
RefPtr<DynamicAtom> atom = DynamicAtom::Create(aUTF16String, hash);
RefPtr<Atom> atom = Atom::CreateDynamic(aUTF16String, hash);
he->mAtom = atom;
return atom.forget();
@ -803,8 +776,7 @@ NS_AtomizeMainThread(const nsAString& aUTF16String)
uint32_t hash;
AtomTableKey key(aUTF16String.Data(), aUTF16String.Length(), &hash);
uint32_t index = hash % RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE;
nsIAtom* atom =
sRecentlyUsedMainThreadAtoms[index];
Atom* atom = sRecentlyUsedMainThreadAtoms[index];
if (atom) {
uint32_t length = atom->GetLength();
if (length == key.mLength &&
@ -821,18 +793,19 @@ NS_AtomizeMainThread(const nsAString& aUTF16String)
if (he->mAtom) {
retVal = he->mAtom;
} else {
retVal = DynamicAtom::Create(aUTF16String, hash);
he->mAtom = retVal;
RefPtr<Atom> newAtom = Atom::CreateDynamic(aUTF16String, hash);
he->mAtom = newAtom;
retVal = newAtom.forget();
}
sRecentlyUsedMainThreadAtoms[index] = retVal;
sRecentlyUsedMainThreadAtoms[index] = he->mAtom;
return retVal.forget();
}
nsrefcnt
NS_GetNumberOfAtoms(void)
{
DynamicAtom::GCAtomTable(); // Trigger a GC so that we return a deterministic result.
Atom::GCAtomTable(); // Trigger a GC so that we return a deterministic result.
MutexAutoLock lock(*gAtomTableLock);
return gAtomTable->EntryCount();
}