Oilpan: Implement a GC to take a heap snapshot

Source/platform/heap/ThreadState.h

 /*
  * 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 160 matching lines @@
     // When garbage collecting we need to know whether or not there
     // can be pointers to Blink GC managed objects on the stack for
     // each thread. When threads reach a safe point they record
     // whether or not they have pointers on the stack.
     enum StackState {
         NoHeapPointersOnStack,
         HeapPointersOnStack
     };
 
     enum GCType {
-        GCWithSweep, // Sweeping is completed in Heap::collectGarbage().
-        GCWithoutSweep, // Lazy sweeping is scheduled.
+        // Run a marking task and a sweeping task in Heap::collectGarbage().
+        GCWithSweep,
+        // Run only a marking task in Heap::collectGarbage(). A sweeping task
+        // is split into chunks and scheduled lazily.
+        GCWithoutSweep,
+        // Run a marking task just to take a heap snapshot. A sweeping task
+        // doesn't run and the marks are just dropped.
+        TakeSnapshot,
     };
 
     // See setGCState() for possible state transitions.
     enum GCState {
         NoGCScheduled,
         IdleGCScheduled,
         PreciseGCScheduled,
         FullGCScheduled,
         StoppingOtherThreads,
         GCRunning,
@@ skipping 140 matching lines @@
     //   has not yet completed its lazy sweeping of the last GC.
     //   In this case, the next GC just cancels the remaining lazy sweeping.
     //   Specifically, preGC() of the next GC calls makeConsistentForGC()
     //   and it marks all not-yet-swept objets as dead.
     void makeConsistentForGC();
     void preGC();
     void postGC(GCType);
     void preSweep();
     void completeSweep();
     void postSweep();
+    // makeConsistentForMutator() drops marks from marked objects and rebuild
+    // free lists. This is called after taking a snapshot and before resuming
+    // the executions of mutators.
+    void makeConsistentForMutator();
 
     // Support for disallowing allocation. Mainly used for sanity
     // checks asserts.
     bool isAllocationAllowed() const { return !isAtSafePoint() && !m_noAllocationCount; }
     void enterNoAllocationScope() { m_noAllocationCount++; }
     void leaveNoAllocationScope() { m_noAllocationCount--; }
     bool isGCForbidden() const { return m_gcForbiddenCount; }
     void enterGCForbiddenScope() { m_gcForbiddenCount++; }
     void leaveGCForbiddenScope() { m_gcForbiddenCount--; }
     bool sweepForbidden() const { return m_sweepForbidden; }
@@ skipping 290 matching lines @@
     // to sweep away any objects that are left on this heap.
     // We assert that nothing must remain after this cleanup.
     // If assertion does not hold we crash as we are potentially
     // in the dangling pointer situation.
     void cleanup();
     void cleanupPages();
 
     void unregisterPreFinalizerInternal(void*);
     void invokePreFinalizers(Visitor&);
 
+    void takeSnapshot();
 #if ENABLE(GC_PROFILING)
     void snapshotFreeList();
 #endif
     void clearHeapAges();
     int heapIndexOfVectorHeapLeastRecentlyExpanded(int beginHeapIndex, int endHeapIndex);
 
     friend class SafePointAwareMutexLocker;
     friend class SafePointBarrier;
     friend class SafePointScope;
 
@@ skipping 72 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 } // namespace blink
 
 #endif // ThreadState_h