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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/202299">202299</a></dd>
<dt>Author</dt> <dd>ggaren@apple.com</dd>
<dt>Date</dt> <dd>2016-06-21 16:06:08 -0700 (Tue, 21 Jun 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>Options::useImmortalObjects is not safe for conservative GC
https://bugs.webkit.org/show_bug.cgi?id=158999
Reviewed by Geoffrey Garen.
useImmortalObjects set the mark bit to keep an object from being
reallocated. This had the negative side-effect of convincing the
conservative marker that the object was a valid and live cell, which
would cause us to visit garbage.
* heap/Heap.cpp:
(JSC::Heap::didFinishCollection):
(JSC::Heap::resumeCompilerThreads):
(JSC::Heap::setFullActivityCallback):
(JSC::Heap::markDeadObjects): Deleted.
* heap/Heap.h: Don't set the mark bit on a dead object. That's a bug in
a conservative GC.
* heap/MarkedAllocator.cpp:
(JSC::MarkedAllocator::retire): New helper.
(JSC::MarkedAllocator::reset): Automatically retire old blocks when
we're doing the immortal objects thing. This has the effect of
preserving memory for debugging because we never recycle a previously
allocated block.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapHeapcpp">trunk/Source/JavaScriptCore/heap/Heap.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapHeaph">trunk/Source/JavaScriptCore/heap/Heap.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedAllocatorcpp">trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMarkedAllocatorh">trunk/Source/JavaScriptCore/heap/MarkedAllocator.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (202298 => 202299)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-06-21 22:46:16 UTC (rev 202298)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-06-21 23:06:08 UTC (rev 202299)
</span><span class="lines">@@ -1,3 +1,31 @@
</span><ins>+2016-06-21 Geoffrey Garen <ggaren@apple.com>
+
+ Options::useImmortalObjects is not safe for conservative GC
+ https://bugs.webkit.org/show_bug.cgi?id=158999
+
+ Reviewed by Geoffrey Garen.
+
+ useImmortalObjects set the mark bit to keep an object from being
+ reallocated. This had the negative side-effect of convincing the
+ conservative marker that the object was a valid and live cell, which
+ would cause us to visit garbage.
+
+ * heap/Heap.cpp:
+ (JSC::Heap::didFinishCollection):
+ (JSC::Heap::resumeCompilerThreads):
+ (JSC::Heap::setFullActivityCallback):
+ (JSC::Heap::markDeadObjects): Deleted.
+ * heap/Heap.h: Don't set the mark bit on a dead object. That's a bug in
+ a conservative GC.
+
+ * heap/MarkedAllocator.cpp:
+ (JSC::MarkedAllocator::retire): New helper.
+
+ (JSC::MarkedAllocator::reset): Automatically retire old blocks when
+ we're doing the immortal objects thing. This has the effect of
+ preserving memory for debugging because we never recycle a previously
+ allocated block.
+
</ins><span class="cx"> 2016-06-21 Anders Carlsson <andersca@apple.com>
</span><span class="cx">
</span><span class="cx"> Begin moving the Apple Pay code to the open source repository
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapHeapcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/Heap.cpp (202298 => 202299)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/Heap.cpp 2016-06-21 22:46:16 UTC (rev 202298)
+++ trunk/Source/JavaScriptCore/heap/Heap.cpp 2016-06-21 23:06:08 UTC (rev 202299)
</span><span class="lines">@@ -252,20 +252,6 @@
</span><span class="cx"> return true;
</span><span class="cx"> }
</span><span class="cx">
</span><del>-struct MarkObject : public MarkedBlock::VoidFunctor {
- inline void visit(JSCell* cell)
- {
- if (cell->isZapped())
- return;
- Heap::heap(cell)->setMarked(cell);
- }
- IterationStatus operator()(JSCell* cell)
- {
- visit(cell);
- return IterationStatus::Continue;
- }
-};
-
</del><span class="cx"> struct Count : public MarkedBlock::CountFunctor {
</span><span class="cx"> void operator()(JSCell*) { count(1); }
</span><span class="cx"> };
</span><span class="lines">@@ -1472,9 +1458,6 @@
</span><span class="cx"> if (Options::useZombieMode())
</span><span class="cx"> zombifyDeadObjects();
</span><span class="cx">
</span><del>- if (Options::useImmortalObjects())
- markDeadObjects();
-
</del><span class="cx"> if (Options::dumpObjectStatistics())
</span><span class="cx"> HeapStatistics::dumpObjectStatistics(this);
</span><span class="cx">
</span><span class="lines">@@ -1503,12 +1486,6 @@
</span><span class="cx"> #endif
</span><span class="cx"> }
</span><span class="cx">
</span><del>-void Heap::markDeadObjects()
-{
- HeapIterationScope iterationScope(*this);
- m_objectSpace.forEachDeadCell<MarkObject>(iterationScope);
-}
-
</del><span class="cx"> void Heap::setFullActivityCallback(PassRefPtr<FullGCActivityCallback> activityCallback)
</span><span class="cx"> {
</span><span class="cx"> m_fullActivityCallback = activityCallback;
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapHeaph"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/Heap.h (202298 => 202299)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/Heap.h 2016-06-21 22:46:16 UTC (rev 202298)
+++ trunk/Source/JavaScriptCore/heap/Heap.h 2016-06-21 23:06:08 UTC (rev 202299)
</span><span class="lines">@@ -342,7 +342,6 @@
</span><span class="cx"> void didFinishCollection(double gcStartTime);
</span><span class="cx"> void resumeCompilerThreads();
</span><span class="cx"> void zombifyDeadObjects();
</span><del>- void markDeadObjects();
</del><span class="cx"> void gatherExtraHeapSnapshotData(HeapProfiler&);
</span><span class="cx"> void removeDeadHeapSnapshotNodes(HeapProfiler&);
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedAllocatorcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp (202298 => 202299)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp 2016-06-21 22:46:16 UTC (rev 202298)
+++ trunk/Source/JavaScriptCore/heap/MarkedAllocator.cpp 2016-06-21 23:06:08 UTC (rev 202299)
</span><span class="lines">@@ -59,6 +59,13 @@
</span><span class="cx"> return false;
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+void MarkedAllocator::retire(MarkedBlock* block, MarkedBlock::FreeList& freeList)
+{
+ m_blockList.remove(block);
+ m_retiredBlocks.push(block);
+ block->didRetireBlock(freeList);
+}
+
</ins><span class="cx"> inline void* MarkedAllocator::tryAllocateHelper(size_t bytes)
</span><span class="cx"> {
</span><span class="cx"> if (m_currentBlock) {
</span><span class="lines">@@ -76,9 +83,7 @@
</span><span class="cx"> double utilization = ((double)MarkedBlock::blockSize - (double)freeList.bytes) / (double)MarkedBlock::blockSize;
</span><span class="cx"> if (utilization >= Options::minMarkedBlockUtilization()) {
</span><span class="cx"> ASSERT(freeList.bytes || !freeList.head);
</span><del>- m_blockList.remove(block);
- m_retiredBlocks.push(block);
- block->didRetireBlock(freeList);
</del><ins>+ retire(block, freeList);
</ins><span class="cx"> continue;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -216,6 +221,16 @@
</span><span class="cx"> m_blockList.append(m_retiredBlocks);
</span><span class="cx">
</span><span class="cx"> m_nextBlockToSweep = m_blockList.head();
</span><ins>+
+ if (UNLIKELY(Options::useImmortalObjects())) {
+ MarkedBlock* next;
+ for (MarkedBlock*& block = m_nextBlockToSweep; block; block = next) {
+ next = block->next();
+
+ MarkedBlock::FreeList freeList = block->sweep(MarkedBlock::SweepToFreeList);
+ retire(block, freeList);
+ }
+ }
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> struct LastChanceToFinalize : MarkedBlock::VoidFunctor {
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMarkedAllocatorh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MarkedAllocator.h (202298 => 202299)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MarkedAllocator.h 2016-06-21 22:46:16 UTC (rev 202298)
+++ trunk/Source/JavaScriptCore/heap/MarkedAllocator.h 2016-06-21 23:06:08 UTC (rev 202299)
</span><span class="lines">@@ -72,6 +72,7 @@
</span><span class="cx"> void* tryPopFreeList(size_t);
</span><span class="cx"> MarkedBlock* allocateBlock(size_t);
</span><span class="cx"> ALWAYS_INLINE void doTestCollectionsIfNeeded();
</span><ins>+ void retire(MarkedBlock*, MarkedBlock::FreeList&);
</ins><span class="cx">
</span><span class="cx"> MarkedBlock::FreeList m_freeList;
</span><span class="cx"> MarkedBlock* m_currentBlock;
</span></span></pre>
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