Oilpan: Defer reusing freed memory for one GC cycle

Source/platform/heap/HeapTest.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 1822 matching lines @@
         Persistent<SimpleFinalizedObject> finalized = SimpleFinalizedObject::create();
         EXPECT_EQ(0, SimpleFinalizedObject::s_destructorCalls);
         Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
         EXPECT_EQ(0, SimpleFinalizedObject::s_destructorCalls);
     }
 
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
     EXPECT_EQ(1, SimpleFinalizedObject::s_destructorCalls);
 }
 
+#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
+TEST(HeapTest, FreelistReuse)
+{
+    clearOutOldGarbage();
+
+    for (int i = 0; i < 100; i++)
+        new IntWrapper(i);
+    IntWrapper* p1 = new IntWrapper(100);
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
+    // In non-production builds, we delay reusing freed memory for at least
+    // one GC cycle.
+    for (int i = 0; i < 100; i++) {
+        IntWrapper* p2 = new IntWrapper(i);
+        EXPECT_NE(p1, p2);
+    }
+
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
+    // Now the freed memory in the first GC should be reused.
+    bool reusedMemoryFound = false;
+    for (int i = 0; i < 10000; i++) {
+        IntWrapper* p2 = new IntWrapper(i);
+        if (p1 == p2) {
+            reusedMemoryFound = true;
+            break;
+        }
+    }
+    EXPECT_TRUE(reusedMemoryFound);
+}
+#endif
+
 #if ENABLE(LAZY_SWEEPING)
 TEST(HeapTest, LazySweepingPages)
 {
     clearOutOldGarbage();
 
     SimpleFinalizedObject::s_destructorCalls = 0;
     EXPECT_EQ(0, SimpleFinalizedObject::s_destructorCalls);
     for (int i = 0; i < 1000; i++)
         SimpleFinalizedObject::create();
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithoutSweep, Heap::ForcedGC);
     EXPECT_EQ(0, SimpleFinalizedObject::s_destructorCalls);
     for (int i = 0; i < 10000; i++)
         SimpleFinalizedObject::create();
     EXPECT_EQ(1000, SimpleFinalizedObject::s_destructorCalls);
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
     EXPECT_EQ(11000, SimpleFinalizedObject::s_destructorCalls);
 }
 
 TEST(HeapTest, LazySweepingLargeObjectPages)
 {
     clearOutOldGarbage();
 
+    // Create free lists that can be reused for IntWrappers created in
+    // LargeHeapObject::create().
+    Persistent<IntWrapper> p1 = new IntWrapper(1);
+    for (int i = 0; i < 100; i++) {
+        new IntWrapper(i);
+    }
+    Persistent<IntWrapper> p2 = new IntWrapper(2);
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
+
     LargeHeapObject::s_destructorCalls = 0;
     EXPECT_EQ(0, LargeHeapObject::s_destructorCalls);
     for (int i = 0; i < 10; i++)
         LargeHeapObject::create();
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithoutSweep, Heap::ForcedGC);
+    EXPECT_EQ(0, LargeHeapObject::s_destructorCalls);
     for (int i = 0; i < 10; i++) {
         LargeHeapObject::create();
         EXPECT_EQ(i + 1, LargeHeapObject::s_destructorCalls);
     }
     LargeHeapObject::create();
     LargeHeapObject::create();
     EXPECT_EQ(10, LargeHeapObject::s_destructorCalls);
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithoutSweep, Heap::ForcedGC);
     EXPECT_EQ(10, LargeHeapObject::s_destructorCalls);
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
@@ skipping 4244 matching lines @@
 {
     Persistent<ClassWithMember> object = ClassWithMember::create();
     EXPECT_EQ(0, object->traceCount());
     TestMixinAllocatingObject* mixin = TestMixinAllocatingObject::create(object.get());
     EXPECT_TRUE(mixin);
     EXPECT_GT(object->traceCount(), 0);
     EXPECT_GT(mixin->traceCount(), 0);
 }
 
 } // namespace blink