Revert of Implement WTF::WeakPtr in terms of base::WeakPtr

third_party/WebKit/Source/wtf/WeakPtr.h

 /*
  * Copyright (C) 2013 Google, Inc. All Rights Reserved.
  *
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  * modification, are permitted provided that the following conditions
  * are met:
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  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 #ifndef WTF_WeakPtr_h
 #define WTF_WeakPtr_h
 
-#include "base/memory/weak_ptr.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefPtr.h"
+#include "wtf/ThreadSafeRefCounted.h"
+#include "wtf/Threading.h"
 
 namespace WTF {
 
 template<typename T>
-using WeakPtr = base::WeakPtr<T>;
+class WeakReference : public ThreadSafeRefCounted<WeakReference<T>> {
+    WTF_MAKE_NONCOPYABLE(WeakReference<T>);
+    USING_FAST_MALLOC(WeakReference);
+public:
+    static PassRefPtr<WeakReference<T>> create(T* ptr) { return adoptRef(new WeakReference(ptr)); }
+    static PassRefPtr<WeakReference<T>> createUnbound() { return adoptRef(new WeakReference()); }
+
+    T* get() const
+    {
+#if DCHECK_IS_ON()
+        DCHECK_EQ(m_boundThread, currentThread());
+#endif
+        return m_ptr;
+    }
+
+    void clear()
+    {
+#if DCHECK_IS_ON()
+        DCHECK_EQ(m_boundThread, currentThread());
+#endif
+        m_ptr = 0;
+    }
+
+    void bindTo(T* ptr)
+    {
+        DCHECK(!m_ptr);
+#if DCHECK_IS_ON()
+        m_boundThread = currentThread();
+#endif
+        m_ptr = ptr;
+    }
+
+private:
+    WeakReference() : m_ptr(0) { }
+
+    explicit WeakReference(T* ptr)
+        : m_ptr(ptr)
+#if DCHECK_IS_ON()
+        , m_boundThread(currentThread())
+#endif
+    {
+    }
+
+    T* m_ptr;
+#if DCHECK_IS_ON()
+    ThreadIdentifier m_boundThread;
+#endif
+};
+
+template<typename T>
+class WeakPtr {
+    USING_FAST_MALLOC(WeakPtr);
+public:
+    WeakPtr() { }
+    WeakPtr(std::nullptr_t) { }
+    WeakPtr(PassRefPtr<WeakReference<T>> ref) : m_ref(ref) { }
+
+    T* get() const { return m_ref ? m_ref->get() : 0; }
+    void clear() { m_ref.clear(); }
+
+    T& operator*() const
+    {
+        DCHECK(get());
+        return *get();
+    }
+
+    T* operator->() const
+    {
+        DCHECK(get());
+        return get();
+    }
+
+    explicit operator bool() const { return get(); }
+
+private:
+    RefPtr<WeakReference<T>> m_ref;
+};
+
+template<typename T, typename U> inline bool operator==(const WeakPtr<T>& a, const WeakPtr<U>& b)
+{
+    return a.get() == b.get();
+}
+
+template<typename T, typename U> inline bool operator!=(const WeakPtr<T>& a, const WeakPtr<U>& b)
+{
+    return a.get() != b.get();
+}
 
 template<typename T>
 class WeakPtrFactory {
     WTF_MAKE_NONCOPYABLE(WeakPtrFactory<T>);
     USING_FAST_MALLOC(WeakPtrFactory);
 public:
-    explicit WeakPtrFactory(T* ptr) : m_factory(ptr) { }
+    explicit WeakPtrFactory(T* ptr) : m_ref(WeakReference<T>::create(ptr)) { }
 
-    WeakPtr<T> createWeakPtr() { return m_factory.GetWeakPtr(); }
+    WeakPtrFactory(PassRefPtr<WeakReference<T>> ref, T* ptr)
+        : m_ref(ref)
+    {
+        m_ref->bindTo(ptr);
+    }
+
+    ~WeakPtrFactory() { m_ref->clear(); }
+
+    // We should consider having createWeakPtr populate m_ref the first time createWeakPtr is called.
+    WeakPtr<T> createWeakPtr() { return WeakPtr<T>(m_ref); }
 
     void revokeAll()
     {
-        m_factory.InvalidateWeakPtrs();
+        T* ptr = m_ref->get();
+        m_ref->clear();
+        // We create a new WeakReference so that future calls to createWeakPtr() create nonzero WeakPtrs.
+        m_ref = WeakReference<T>::create(ptr);
     }
 
     bool hasWeakPtrs() const
     {
-        return m_factory.HasWeakPtrs();
+        return m_ref->refCount() > 1;
     }
 
 private:
-    base::WeakPtrFactory<T> m_factory;
+    RefPtr<WeakReference<T>> m_ref;
 };
 
 } // namespace WTF
 
 using WTF::WeakPtr;
 using WTF::WeakPtrFactory;
+using WTF::WeakReference;
 
 #endif