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Bug 850523 (part 2) - Use C++ comments in LifoAlloc.{cpp,h}. r=wmccloskey.

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--HG--
extra : rebase_source : 395321642042559ef2484445fa13c03ba22e8390
This commit is contained in:
Nicholas Nethercote 2013-03-14 15:10:39 -07:00
parent 9c517940e3
commit 59579d6d63
2 changed files with 54 additions and 72 deletions
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26
js/src/ds/LifoAlloc.cpp
View File

@ -21,11 +21,9 @@ BumpChunk::new_(size_t chunkSize)
return NULL;
BumpChunk *result = new (mem) BumpChunk(chunkSize - sizeof(BumpChunk));
/*
* We assume that the alignment of sAlign is less than that of
* the underlying memory allocator -- creating a new BumpChunk should
* always satisfy the sAlign alignment constraint.
*/
// We assume that the alignment of sAlign is less than that of
// the underlying memory allocator -- creating a new BumpChunk should
// always satisfy the sAlign alignment constraint.
JS_ASSERT(AlignPtr(result->bump) == result->bump);
return result;
}
@ -51,8 +49,8 @@ BumpChunk::canAlloc(size_t n)
return bumped <= limit && bumped > headerBase();
}
} /* namespace detail */
} /* namespace js */
} // namespace detail
} // namespace js
void
LifoAlloc::freeAll()
@ -65,10 +63,8 @@ LifoAlloc::freeAll()
}
first = latest = last = NULL;
/*
* Nb: maintaining curSize_ correctly isn't easy. Fortunately, this is an
* excellent sanity check.
*/
// Nb: maintaining curSize_ correctly isn't easy. Fortunately, this is an
// excellent sanity check.
JS_ASSERT(curSize_ == 0);
}
@ -76,10 +72,10 @@ LifoAlloc::BumpChunk *
LifoAlloc::getOrCreateChunk(size_t n)
{
if (first) {
/* Look for existing, unused BumpChunks to satisfy the request. */
// Look for existing, unused BumpChunks to satisfy the request.
while (latest->next()) {
latest = latest->next();
latest->resetBump(); /* This was an unused BumpChunk on the chain. */
latest->resetBump(); // This was an unused BumpChunk on the chain.
if (latest->canAlloc(n))
return latest;
}
@ -90,7 +86,7 @@ LifoAlloc::getOrCreateChunk(size_t n)
if (n > defaultChunkFreeSpace) {
size_t allocSizeWithHeader = n + sizeof(BumpChunk);
/* Guard for overflow. */
// Guard for overflow.
if (allocSizeWithHeader < n ||
(allocSizeWithHeader & (size_t(1) << (tl::BitSize<size_t>::result - 1)))) {
return NULL;
@ -101,7 +97,7 @@ LifoAlloc::getOrCreateChunk(size_t n)
chunkSize = defaultChunkSize_;
}
/* If we get here, we couldn't find an existing BumpChunk to fill the request. */
// If we get here, we couldn't find an existing BumpChunk to fill the request.
BumpChunk *newChunk = BumpChunk::new_(chunkSize);
if (!newChunk)
return NULL;

100
js/src/ds/LifoAlloc.h
View File

@ -14,12 +14,10 @@
#include "mozilla/MemoryChecking.h"
#include "mozilla/TypeTraits.h"
/*
* This data structure supports stacky LIFO allocation (mark/release and
* LifoAllocScope). It does not maintain one contiguous segment; instead, it
* maintains a bunch of linked memory segments. In order to prevent malloc/free
* thrashing, unused segments are deallocated when garbage collection occurs.
*/
// This data structure supports stacky LIFO allocation (mark/release and
// LifoAllocScope). It does not maintain one contiguous segment; instead, it
// maintains a bunch of linked memory segments. In order to prevent malloc/free
// thrashing, unused segments are deallocated when garbage collection occurs.
#include "jsutil.h"
@ -44,13 +42,13 @@ AlignPtr(void *orig)
return result;
}
/* Header for a chunk of memory wrangled by the LifoAlloc. */
// Header for a chunk of memory wrangled by the LifoAlloc.
class BumpChunk
{
char *bump; /* start of the available data */
char *limit; /* end of the data */
BumpChunk *next_; /* the next BumpChunk */
size_t bumpSpaceSize; /* size of the data area */
char *bump; // start of the available data
char *limit; // end of the data
BumpChunk *next_; // the next BumpChunk
size_t bumpSpaceSize; // size of the data area
char *headerBase() { return reinterpret_cast<char *>(this); }
char *bumpBase() const { return limit - bumpSpaceSize; }
@ -75,12 +73,12 @@ class BumpChunk
#ifdef DEBUG
JS_ASSERT(contains(prevBump));
/* Clobber the now-free space. */
// Clobber the now-free space.
if (prevBump > bump)
memset(bump, 0xcd, prevBump - bump);
#endif
/* Poison/Unpoison memory that we just free'd/allocated */
// Poison/Unpoison memory that we just free'd/allocated.
#if defined(MOZ_HAVE_MEM_CHECKS)
if (prevBump > bump)
MOZ_MAKE_MEM_NOACCESS(bump, prevBump - bump);
@ -125,7 +123,7 @@ class BumpChunk
return limit - AlignPtr(bump);
}
/* Try to perform an allocation of size |n|, return null if not possible. */
// Try to perform an allocation of size |n|, return null if not possible.
JS_ALWAYS_INLINE
void *tryAlloc(size_t n) {
char *aligned = AlignPtr(bump);
@ -134,11 +132,11 @@ class BumpChunk
if (newBump > limit)
return NULL;
/* Check for overflow. */
// Check for overflow.
if (JS_UNLIKELY(newBump < bump))
return NULL;
JS_ASSERT(canAlloc(n)); /* Ensure consistency between "can" and "try". */
JS_ASSERT(canAlloc(n)); // Ensure consistency between "can" and "try".
setBump(newBump);
return aligned;
}
@ -153,14 +151,12 @@ class BumpChunk
static void delete_(BumpChunk *chunk);
};
} /* namespace detail */
} // namespace detail
/*
* LIFO bump allocator: used for phase-oriented and fast LIFO allocations.
*
* Note: |latest| is not necessary "last". We leave BumpChunks latent in the
* chain after they've been released to avoid thrashing before a GC.
*/
// LIFO bump allocator: used for phase-oriented and fast LIFO allocations.
//
// Note: |latest| is not necessary "last". We leave BumpChunks latent in the
// chain after they've been released to avoid thrashing before a GC.
class LifoAlloc
{
typedef detail::BumpChunk BumpChunk;
@ -176,13 +172,11 @@ class LifoAlloc
void operator=(const LifoAlloc &) MOZ_DELETE;
LifoAlloc(const LifoAlloc &) MOZ_DELETE;
/*
* Return a BumpChunk that can perform an allocation of at least size |n|
* and add it to the chain appropriately.
*
* Side effect: if retval is non-null, |first| and |latest| are initialized
* appropriately.
*/
// Return a BumpChunk that can perform an allocation of at least size |n|
// and add it to the chain appropriately.
//
// Side effect: if retval is non-null, |first| and |latest| are initialized
// appropriately.
BumpChunk *getOrCreateChunk(size_t n);
void reset(size_t defaultChunkSize) {
@ -219,14 +213,12 @@ class LifoAlloc
reset(defaultChunkSize);
}
/* Steal allocated chunks from |other|. */
// Steal allocated chunks from |other|.
void steal(LifoAlloc *other) {
JS_ASSERT(!other->markCount);
/*
* Copy everything from |other| to |this| except for |peakSize_|, which
* requires some care.
*/
// Copy everything from |other| to |this| except for |peakSize_|, which
// requires some care.
size_t oldPeakSize = peakSize_;
PodCopy((char *) this, (char *) other, sizeof(*this));
peakSize_ = Max(oldPeakSize, curSize_);
@ -234,17 +226,17 @@ class LifoAlloc
other->reset(defaultChunkSize_);
}
/* Append all chunks from |other|. They are removed from |other|. */
// Append all chunks from |other|. They are removed from |other|.
void transferFrom(LifoAlloc *other);
/* Append unused chunks from |other|. They are removed from |other|. */
// Append unused chunks from |other|. They are removed from |other|.
void transferUnusedFrom(LifoAlloc *other);
~LifoAlloc() { freeAll(); }
size_t defaultChunkSize() const { return defaultChunkSize_; }
/* Frees all held memory. */
// Frees all held memory.
void freeAll();
JS_ALWAYS_INLINE
@ -301,10 +293,8 @@ class LifoAlloc
return (T *) mem;
}
/*
* Create an array with uninitialized elements of type |T|.
* The caller is responsible for initialization.
*/
// Create an array with uninitialized elements of type |T|.
// The caller is responsible for initialization.
template <typename T>
T *newArrayUninitialized(size_t count) {
return static_cast<T *>(alloc(sizeof(T) * count));
@ -326,11 +316,9 @@ class LifoAlloc
return;
}
/*
* Find the chunk that contains |mark|, and make sure we don't pass
* |latest| along the way -- we should be making the chain of active
* chunks shorter, not longer!
*/
// Find the chunk that contains |mark|, and make sure we don't pass
// |latest| along the way -- we should be making the chain of active
// chunks shorter, not longer!
BumpChunk *container;
for (container = first; !container->contains(mark); container = container->next())
JS_ASSERT(container != latest);
@ -346,7 +334,7 @@ class LifoAlloc
latest->resetBump();
}
/* Get the total "used" (occupied bytes) count for the arena chunks. */
// Get the total "used" (occupied bytes) count for the arena chunks.
size_t used() const {
size_t accum = 0;
for (BumpChunk *chunk = first; chunk; chunk = chunk->next()) {
@ -357,29 +345,27 @@ class LifoAlloc
return accum;
}
/* Get the total size of the arena chunks (including unused space). */
// Get the total size of the arena chunks (including unused space).
size_t sizeOfExcludingThis(JSMallocSizeOfFun mallocSizeOf) const {
size_t n = 0;
for (BumpChunk *chunk = first; chunk; chunk = chunk->next())
n += chunk->sizeOfIncludingThis(mallocSizeOf);
/* While we're here, let's sanity check curSize_. */
// While we're here, let's sanity check curSize_.
MOZ_ASSERT(curSize_ == n);
return n;
}
/* Like sizeOfExcludingThis(), but includes the size of the LifoAlloc itself. */
// Like sizeOfExcludingThis(), but includes the size of the LifoAlloc itself.
size_t sizeOfIncludingThis(JSMallocSizeOfFun mallocSizeOf) const {
return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
}
/*
* Get the peak size of the arena chunks (including unused space and
* bookkeeping space).
*/
// Get the peak size of the arena chunks (including unused space and
// bookkeeping space).
size_t peakSizeOfExcludingThis() const { return peakSize_; }
/* Doesn't perform construction; useful for lazily-initialized POD types. */
// Doesn't perform construction; useful for lazily-initialized POD types.
template <typename T>
JS_ALWAYS_INLINE
T *newPod() {
@ -421,6 +407,6 @@ class LifoAllocScope
}
};
} /* namespace js */
} // namespace js
#endif