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Bug 937818, part 4 - Exceeded refcount nodes should already be black. r=smaug

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Due to graph mutation during an incremental cycle collection, objects in the CC graph
may end up with more things pointing to them than they have a ref count. However, these
objects should never become garbage.
This commit is contained in:
Andrew McCreight 2013-12-17 19:29:57 -08:00
parent 84c4a3a065
commit b2c805070f
1 changed files with 16 additions and 5 deletions
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21
xpcom/base/nsCycleCollector.cpp
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@ -2406,8 +2406,9 @@ private:
struct scanVisitor
{
scanVisitor(uint32_t &aWhiteNodeCount, bool &aFailed)
: mWhiteNodeCount(aWhiteNodeCount), mFailed(aFailed)
scanVisitor(uint32_t &aWhiteNodeCount, bool &aFailed, bool aWasIncremental)
: mWhiteNodeCount(aWhiteNodeCount), mFailed(aFailed),
mWasIncremental(aWasIncremental)
{
}
@ -2418,8 +2419,16 @@ struct scanVisitor
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) {
// If we found more references to an object than its ref count, then
// the object should have already been marked as an incremental
// root. Note that this is imprecise, because pi could have been
// marked black for other reasons. Always fault if we weren't
// incremental, as there were no incremental roots in that case.
if (!mWasIncremental || pi->mColor != black) {
Fault("traversed refs exceed refcount", pi);
}
}
if (pi->mInternalRefs == pi->mRefCount || pi->mRefCount == 0) {
pi->mColor = white;
@ -2438,6 +2447,7 @@ struct scanVisitor
private:
uint32_t &mWhiteNodeCount;
bool &mFailed;
bool mWasIncremental;
};
// Iterate over the WeakMaps. If we mark anything while iterating
@ -2606,7 +2616,8 @@ nsCycleCollector::ScanRoots(bool aFullySynchGraphBuild)
// probably faster to use a GraphWalker than a
// NodePool::Enumerator.
bool failed = false;
GraphWalker<scanVisitor>(scanVisitor(mWhiteNodeCount, failed)).WalkFromRoots(mGraph);
scanVisitor sv(mWhiteNodeCount, failed, !aFullySynchGraphBuild);
GraphWalker<scanVisitor>(sv).WalkFromRoots(mGraph);
timeLog.Checkpoint("ScanRoots::WalkFromRoots");
if (failed) {