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Bug 1094564 - Used SegmentedArray in SnowWhiteKiller. r=smaug.

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This patch generalizes SegmentedArray a little, and then uses it instead of
nsTArray in SnowWhiteKiller. This avoids some large (sometimes 1 MiB or more)
allocations which were usually mostly unused.
This commit is contained in:
Nicholas Nethercote 2014-11-09 14:57:09 -08:00
parent b5fe55c53e
commit f64f8ba285
1 changed files with 62 additions and 40 deletions
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102
xpcom/base/nsCycleCollector.cpp
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@ -2465,16 +2465,18 @@ MayHaveChild(void* aObj, nsCycleCollectionParticipant* aCp)
return cf.MayHaveChild();
}
template<class T>
template<class T, size_t N>
class SegmentedArrayElement
: public LinkedListElement<SegmentedArrayElement<T>>
, public AutoFallibleTArray<T, 60>
: public LinkedListElement<SegmentedArrayElement<T, N>>
, public AutoFallibleTArray<T, N>
{
};
template<class T>
template<class T, size_t N>
class SegmentedArray
{
typedef SegmentedArrayElement<T, N> Segment;
public:
~SegmentedArray()
{
@ -2483,9 +2485,9 @@ public:
void AppendElement(T& aElement)
{
SegmentedArrayElement<T>* last = mSegments.getLast();
Segment* last = mSegments.getLast();
if (!last || last->Length() == last->Capacity()) {
last = new SegmentedArrayElement<T>();
last = new Segment();
mSegments.insertBack(last);
}
last->AppendElement(aElement);
@ -2493,24 +2495,29 @@ public:
void Clear()
{
SegmentedArrayElement<T>* first;
Segment* first;
while ((first = mSegments.popFirst())) {
delete first;
}
}
SegmentedArrayElement<T>* GetFirstSegment()
Segment* GetFirstSegment()
{
return mSegments.getFirst();
}
bool IsEmpty()
const Segment* GetFirstSegment() const
{
return mSegments.getFirst();
}
bool IsEmpty() const
{
return !GetFirstSegment();
}
private:
mozilla::LinkedList<SegmentedArrayElement<T>> mSegments;
mozilla::LinkedList<Segment> mSegments;
};
// JSPurpleBuffer keeps references to GCThings which might affect the
@ -2553,8 +2560,8 @@ public:
// pointers which may point into the nursery. The purple buffer never contains
// pointers to the nursery because nursery gcthings can never be gray and only
// gray things can be inserted into the purple buffer.
SegmentedArray<JS::Value> mValues;
SegmentedArray<JSObject*> mObjects;
SegmentedArray<JS::Value, 60> mValues;
SegmentedArray<JSObject*, 60> mObjects;
};
NS_IMPL_CYCLE_COLLECTION_CLASS(JSPurpleBuffer)
@ -2588,42 +2595,58 @@ NS_IMPL_CYCLE_COLLECTION_TRACE_END
NS_IMPL_CYCLE_COLLECTION_ROOT_NATIVE(JSPurpleBuffer, AddRef)
NS_IMPL_CYCLE_COLLECTION_UNROOT_NATIVE(JSPurpleBuffer, Release)
struct SnowWhiteObject
{
void* mPointer;
nsCycleCollectionParticipant* mParticipant;
nsCycleCollectingAutoRefCnt* mRefCnt;
};
class SnowWhiteKiller : public TraceCallbacks
{
struct SnowWhiteObject
{
void* mPointer;
nsCycleCollectionParticipant* mParticipant;
nsCycleCollectingAutoRefCnt* mRefCnt;
};
// Segments are 4 KiB on 32-bit and 8 KiB on 64-bit.
static const size_t kIdealSegmentSize = sizeof(void*) * 1024;
static const size_t kSingleElemSegmentSize =
sizeof(SegmentedArrayElement<SnowWhiteObject, 1>);
static const size_t kSegmentCapacity =
(kIdealSegmentSize - kSingleElemSegmentSize) / sizeof(SnowWhiteObject) + 1;
static const size_t kActualSegmentSize =
sizeof(SegmentedArrayElement<SnowWhiteObject, kSegmentCapacity>);
typedef SegmentedArray<SnowWhiteObject, kSegmentCapacity> ObjectsArray;
public:
SnowWhiteKiller(nsCycleCollector* aCollector, uint32_t aMaxCount)
: mCollector(aCollector)
, mObjects()
{
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;
}
// The segment capacity should be such that the actual segment size is as
// close as possible to the ideal segment size.
static_assert(
kIdealSegmentSize - kActualSegmentSize <= sizeof(SnowWhiteObject),
"ill-sized SnowWhiteKiller segments"
);
}
~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->Trace(o.mPointer, *this, nullptr);
o.mParticipant->DeleteCycleCollectable(o.mPointer);
auto segment = mObjects.GetFirstSegment();
while (segment) {
for (uint32_t i = 0; i < segment->Length(); i++) {
SnowWhiteObject& o = segment->ElementAt(i);
if (!o.mRefCnt->get() && !o.mRefCnt->IsInPurpleBuffer()) {
mCollector->RemoveObjectFromGraph(o.mPointer);
o.mRefCnt->stabilizeForDeletion();
o.mParticipant->Trace(o.mPointer, *this, nullptr);
o.mParticipant->DeleteCycleCollectable(o.mPointer);
}
}
segment = segment->getNext();
}
mObjects.Clear();
}
void
@ -2635,15 +2658,14 @@ public:
nsCycleCollectionParticipant* cp = aEntry->mParticipant;
CanonicalizeParticipant(&o, &cp);
SnowWhiteObject swo = { o, cp, aEntry->mRefCnt };
if (mObjects.AppendElement(swo)) {
aBuffer.Remove(aEntry);
}
mObjects.AppendElement(swo);
aBuffer.Remove(aEntry);
}
}
bool HasSnowWhiteObjects() const
{
return mObjects.Length() > 0;
return !mObjects.IsEmpty();
}
virtual void Trace(JS::Heap<JS::Value>* aValue, const char* aName,
@ -2701,7 +2723,7 @@ public:
private:
nsCycleCollector* mCollector;
FallibleTArray<SnowWhiteObject> mObjects;
ObjectsArray mObjects;
};
class RemoveSkippableVisitor : public SnowWhiteKiller