1  /*
 2   * Copyright (C) 2019 Apple, Inc. All rights reserved.
 3   *
 4   * Redistribution and use in source and binary forms, with or without
 5   * modification, are permitted provided that the following conditions
 6   * are met:
 7   * 1. Redistributions of source code must retain the above copyright
 8   *    notice, this list of conditions and the following disclaimer.
 9   * 2. Redistributions in binary form must reproduce the above copyright
10   *    notice, this list of conditions and the following disclaimer in the
11   *    documentation and/or other materials provided with the distribution.
12   *
13   * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14   * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21   * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24   */
25  
26  #include "config.h"
27  #include "JSWeakObjectRef.h"
28  
29  #include "JSCInlines.h"
30  
31  namespace JSC {
32  
33  const ClassInfo JSWeakObjectRef::s_info = { "WeakRef", &Base::s_info, nullptr, nullptr, CREATE_METHOD_TABLE(JSWeakObjectRef) };
34  
35  void JSWeakObjectRef::finishCreation(VM& vm, JSObject* value)
36  {
37      m_lastAccessVersion = vm.currentWeakRefVersion();
38      m_value.set(vm, this, value);
39      Base::finishCreation(vm);
40  }
41  
42  void JSWeakObjectRef::visitChildren(JSCell* cell, SlotVisitor& visitor)
43  {
44      auto* thisObject = jsCast<JSWeakObjectRef*>(cell);
45      ASSERT_GC_OBJECT_INHERITS(thisObject, info());
46      Base::visitChildren(thisObject, visitor);
47      // This doesn't need to be atomic because if we are out of date we will get write barriered and revisit ourselves.
48      if (visitor.vm().currentWeakRefVersion() == thisObject->m_lastAccessVersion) {
49          ASSERT(thisObject->m_value);
50          visitor.append(thisObject->m_value);
51      }
52  }
53  
54  void JSWeakObjectRef::finalizeUnconditionally(VM& vm)
55  {
56      if (m_value && !vm.heap.isMarked(m_value.get()))
57          m_value.clear();
58  }
59  
60  }
61