Oilpan: support eager finalization/sweeping.

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 699866a4516830374b32646ac8351c86a8c97e33..b9213bd5321fe46ef6f308ec4d52ec93387a05f6 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -912,6 +912,7 @@ void ThreadState::preSweep()
     } else {
         // The default behavior is lazy sweeping.
         setGCState(Sweeping);
+        eagerSweep();
         scheduleIdleLazySweep();
     }
 #else
@@ -926,6 +927,31 @@ void ThreadState::preSweep()
 #endif
 }
 
+void ThreadState::eagerSweep()
+{
+    // Some objects need to be finalized promptly and cannot be handled
+    // by lazy sweeping. Keep those in a designated heap and sweep it
+    // eagerly.
+    ASSERT(isSweepingInProgress());
+    ASSERT(!sweepForbidden());

[haraken, 2015/05/19 23:23:37]

I think this should be:

  if (sweepForbidden())
    return;

See the comment in completeSweep() when sweepForbidden() can become true.

[sof, 2015/05/20 09:43:01]

Done + xref'ed the comment.

+
+    ThreadState::SweepForbiddenScope scope(this);
+    {
+        if (isMainThread())
+            ScriptForbiddenScope::enter();
+
+        TRACE_EVENT0("blink_gc", "ThreadState::eagerSweep");
+        double timeStamp = WTF::currentTimeMS();

[haraken, 2015/05/19 23:23:37]

Remove this (see below).

[sof, 2015/05/20 09:43:01]

Removed.

+
+        m_heaps[EagerSweepHeapIndex]->completeSweep();
+
+        Platform::current()->histogramCustomCounts("BlinkGC.EagerSweep", WTF::currentTimeMS() - timeStamp, 0, 10 * 1000, 50);

[haraken, 2015/05/19 23:23:37]

This UMA doesn't exist (and wouldn't be worth adding). So remove this.

+
+        if (isMainThread())
+            ScriptForbiddenScope::exit();
+    }
+}
+
 void ThreadState::completeSweep()
 {
     // If we are not in a sweeping phase, there is nothing to do here.