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 47d9c817abe92f99d5994400413fcd7d15f2993e..1ef1d11ab3cad926f2f4719da4ec47ae1f4aa177 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -850,6 +850,13 @@ void ThreadState::makeConsistentForGC()
         m_heaps[i]->makeConsistentForGC();
 }
 
+void ThreadState::makeConsistentForMutator()
+{
+    ASSERT(isInGC());
+    for (int i = 0; i < NumberOfHeaps; ++i)
+        m_heaps[i]->makeConsistentForMutator();
+}
+
 void ThreadState::preGC()
 {
     ASSERT(!isInGC());
@@ -882,9 +889,23 @@ 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();
+
+        // This unmarks all marked objects and marks all unmarked objects dead.
+        makeConsistentForMutator();
+
+        // Force setting NoGCScheduled to circumvent checkThread()
+        // in setGCState().
+        m_gcState = NoGCScheduled;

[sof, 2015/05/28 12:15:13]

Why are you doing this (way)?

[haraken, 2015/05/28 12:33:36]

As commented above, if we call setGCState(NoGCScheduled) then we hit an ASSERT
in checkThread(), because NoGCScheduled is expected to be set by each thread.
Here we're violating the rule.

One way to fix it would be to remove the checkThread().

Another way would be to introduce a NoSweepScheduled state so that preSweep()
(which is called in each thread) can call setGCState(NoGCScheduled). But we
won't want to introduce another GCState...

Any better idea?

+    }
 }
 
 void ThreadState::preSweep()
@@ -1269,6 +1290,12 @@ 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)
 {