CrossThreadPersistentRegion will only trace objects belonging to the current GCing ThreadHeap

third_party/WebKit/Source/platform/heap/PersistentNode.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/heap/PersistentNode.h"
 
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
@@ skipping 55 matching lines @@
     }
     Persistent<DummyGCBase>* persistent = reinterpret_cast<Persistent<DummyGCBase>*>(self);
     persistent->clear();
     ASSERT(persistentNode->isUnused());
 }
 
 // This function traces all PersistentNodes. If we encounter
 // a PersistentNodeSlot that contains only freed PersistentNodes,
 // we delete the PersistentNodeSlot. This function rebuilds the free
 // list of PersistentNodes.
-void PersistentRegion::tracePersistentNodes(Visitor* visitor)
+void PersistentRegion::tracePersistentNodes(Visitor* visitor, ShouldTraceCallback shouldTrace)
 {
     size_t debugMarkedObjectSize = ProcessHeap::totalMarkedObjectSize();
     base::debug::Alias(&debugMarkedObjectSize);
 
     m_freeListHead = nullptr;
     int persistentCount = 0;
     PersistentNodeSlots** prevNext = &m_slots;
     PersistentNodeSlots* slots = m_slots;
     while (slots) {
         PersistentNode* freeListNext = nullptr;
         PersistentNode* freeListLast = nullptr;
         int freeCount = 0;
         for (int i = 0; i < PersistentNodeSlots::slotCount; ++i) {
             PersistentNode* node = &slots->m_slot[i];
             if (node->isUnused()) {
                 if (!freeListNext)
                     freeListLast = node;
                 node->setFreeListNext(freeListNext);
                 freeListNext = node;
                 ++freeCount;
             } else {
+                ++persistentCount;
+                if (!shouldTrace(visitor, node))
+                    continue;
                 node->tracePersistentNode(visitor);
-                ++persistentCount;
                 debugMarkedObjectSize = ProcessHeap::totalMarkedObjectSize();
             }
         }
         if (freeCount == PersistentNodeSlots::slotCount) {
             PersistentNodeSlots* deadSlots = slots;
             *prevNext = slots->m_next;
             slots = slots->m_next;
             delete deadSlots;
         } else {
             if (freeListLast) {
                 ASSERT(freeListNext);
                 ASSERT(!freeListLast->freeListNext());
                 freeListLast->setFreeListNext(m_freeListHead);
                 m_freeListHead = freeListNext;
             }
             prevNext = &slots->m_next;
             slots = slots->m_next;
         }
     }
     ASSERT(persistentCount == m_persistentCount);
 }
 
+bool CrossThreadPersistentRegion::shouldTracePersistentNode(Visitor* visitor, PersistentNode* node)
+{
+    CrossThreadPersistent<DummyGCBase>* persistent = reinterpret_cast<CrossThreadPersistent<DummyGCBase>*>(node->self());
+    ASSERT(persistent);
+    Address rawObject = reinterpret_cast<Address>(persistent->get());
+    if (!rawObject)
+        return false;
+    return &visitor->heap() == &ThreadState::fromObject(rawObject)->heap();
+}
+
 void CrossThreadPersistentRegion::prepareForThreadStateTermination(ThreadState* threadState)
 {
     // For heaps belonging to a thread that's detaching, any cross-thread persistents
     // pointing into them needs to be disabled. Do that by clearing out the underlying
     // heap reference.
     MutexLocker lock(m_mutex);
 
     // TODO(sof): consider ways of reducing overhead. (e.g., tracking number of active
     // CrossThreadPersistent<>s pointing into the heaps of each ThreadState and use that
     // count to bail out early.)
@@ skipping 16 matching lines @@
             if (page->orphaned())
                 continue;
             if (page->arena()->getThreadState() == threadState)
                 persistent->clear();
         }
         slots = slots->m_next;
     }
 }
 
 } // namespace blink