Oilpan: Implement a GC to take a heap snapshot

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index eefce3ea7d2444e3dda43b92cd739fc64e8c8d56..b478a51002e467856f2553c6408948ab67046969 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -838,19 +838,19 @@ void ThreadState::flushHeapDoesNotContainCacheIfNeeded()
     }
 }
 
-void ThreadState::makeConsistentForSweeping()
+void ThreadState::makeConsistentForSweeping(GCType gcType)
 {
     ASSERT(isInGC());
     TRACE_EVENT0("blink_gc", "ThreadState::makeConsistentForSweeping");
     for (int i = 0; i < NumberOfHeaps; ++i)
-        m_heaps[i]->makeConsistentForSweeping();
+        m_heaps[i]->makeConsistentForSweeping(gcType);
 }
 
-void ThreadState::preGC()
+void ThreadState::preGC(GCType gcType)
 {
     ASSERT(!isInGC());
     setGCState(GCRunning);
-    makeConsistentForSweeping();
+    makeConsistentForSweeping(gcType);
     prepareRegionTree();
     flushHeapDoesNotContainCacheIfNeeded();
     clearHeapAges();
@@ -878,9 +878,21 @@ void ThreadState::postGC(GCType gcType)
     }
 #endif
 
-    setGCState(gcType == GCWithSweep ? EagerSweepScheduled : LazySweepScheduled);
     for (int i = 0; i < NumberOfHeaps; i++)
         m_heaps[i]->prepareForSweep();
+
+    if (gcType == GCWithSweep) {
+        setGCState(EagerSweepScheduled);
+    } else if (gcType == GCWithoutSweep) {
+        setGCState(LazySweepScheduled);
+    } else {
+        takeSnapshot();

[ssid, 2015/05/27 12:43:47]

Sorry, I just realized. This takeSnapshot() should be called before
prepareForSweep().
Also, should prepareForSweep() be called for a GC without sweeping? I see this
method moves pages to other list. Will this be undone?
In any case, i think this should be before the call.

[haraken, 2015/05/27 13:48:10]

prepareForSweep() needs to be called, because the following
makeConsistentForSweeping() works only on the list of unswept pages. If we don't
call prepareForSweep(), all pages are in the list of swept pages and thus we'll
fail at unmarking the marked objects etc.

It is possible to move prepareForSweep() to after takeSnapshot(), but it won't
matter much. If we don't move it, takeSnapshot() needs to scan the list of
unswept pages. If we move it, takeSnapshot() needs to scan the list of swept
pages. That's the only difference, I guess.

+        // This unmarks all marked objects and marks all unmarked objects dead.
+        makeConsistentForSweeping(gcType);
+        // Force setting NoGCScheduled to circumvent checkThread()
+        // in setGCState().
+        m_gcState = NoGCScheduled;
+    }
 }
 
 void ThreadState::preSweep()
@@ -1265,6 +1277,12 @@ void ThreadState::promptlyFreed(size_t gcInfoIndex)
     m_likelyToBePromptlyFreed[entryIndex] += 3;
 }
 
+void ThreadState::takeSnapshot()
+{
+    ASSERT(isInGC());
+    // TODO(ssid): Implement this.
+}
+
 #if ENABLE(GC_PROFILING)
 const GCInfo* ThreadState::findGCInfoFromAllThreads(Address address)
 {