Oilpan: Implement a GC to take a heap snapshot

Source/platform/heap/ThreadState.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 832 matching lines @@
 }
 
 void ThreadState::makeConsistentForGC()
 {
     ASSERT(isInGC());
     TRACE_EVENT0("blink_gc", "ThreadState::makeConsistentForGC");
     for (int i = 0; i < NumberOfHeaps; ++i)
         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());
     setGCState(GCRunning);
     makeConsistentForGC();
     prepareRegionTree();
     flushHeapDoesNotContainCacheIfNeeded();
     clearHeapAges();
 }
 
@@ skipping 12 matching lines @@
         bool disabledByDefaultGCTracingEnabled;
         TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("blink_gc"), &disabledByDefaultGCTracingEnabled);
 
         snapshot();
         if (disabledByDefaultGCTracingEnabled)
             collectAndReportMarkSweepStats();
         incrementMarkedObjectsAge();
     }
 #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()
 {
     checkThread();
     if (gcState() != EagerSweepScheduled && gcState() != LazySweepScheduled)
         return;
 
     {
         if (isMainThread())
@@ skipping 364 matching lines @@
         m_vectorBackingHeapIndex = heapIndexOfVectorHeapLeastRecentlyExpanded(Vector1HeapIndex, Vector4HeapIndex);
 }
 
 void ThreadState::promptlyFreed(size_t gcInfoIndex)
 {
     size_t entryIndex = gcInfoIndex & likelyToBePromptlyFreedArrayMask;
     // See the comment in vectorBackingHeap() for why this is +3.
     m_likelyToBePromptlyFreed[entryIndex] += 3;
 }
 
+void ThreadState::takeSnapshot()
+{
+    ASSERT(isInGC());
+    // TODO(ssid): Implement this.
+}
+
 #if ENABLE(GC_PROFILING)
 const GCInfo* ThreadState::findGCInfoFromAllThreads(Address address)
 {
     bool needLockForIteration = !ThreadState::current()->isInGC();
     if (needLockForIteration)
         threadAttachMutex().lock();
 
     for (ThreadState* state : attachedThreads()) {
         if (const GCInfo* gcInfo = state->findGCInfo(address)) {
             if (needLockForIteration)
@@ skipping 70 matching lines @@
         json->beginArray(it->key.ascii().data());
         for (size_t age = 0; age <= maxHeapObjectAge; ++age)
             json->pushInteger(it->value.ages[age]);
         json->endArray();
     }
     TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(TRACE_DISABLED_BY_DEFAULT("blink_gc"), statsName, this, json.release());
 }
 #endif
 
 } // namespace blink