Oilpan: Defer reusing freed memory for one GC cycle

Source/platform/heap/HeapTest.cpp

Index: Source/platform/heap/HeapTest.cpp
diff --git a/Source/platform/heap/HeapTest.cpp b/Source/platform/heap/HeapTest.cpp
index 44778f8909cd5c5ff70f625de72fc531c2f0fda1..f5423502b17e4977c5cd4b71a0a55a9affac76ad 100644
--- a/Source/platform/heap/HeapTest.cpp
+++ b/Source/platform/heap/HeapTest.cpp
@@ -1903,6 +1903,37 @@ TEST(HeapTest, SimpleFinalization)
     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)
 {
@@ -1925,11 +1956,22 @@ 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);