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      1 /*
      2  * Copyright (C) 2011 Google 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  *
      8  * 1.  Redistributions of source code must retain the above copyright
      9  *     notice, this list of conditions and the following disclaimer.
     10  * 2.  Redistributions in binary form must reproduce the above copyright
     11  *     notice, this list of conditions and the following disclaimer in the
     12  *     documentation and/or other materials provided with the distribution.
     13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     14  *     its contributors may be used to endorse or promote products derived
     15  *     from this software without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 #ifndef SQLCallbackWrapper_h
     29 #define SQLCallbackWrapper_h
     30 
     31 #include "core/dom/ExecutionContext.h"
     32 #include "core/dom/ExecutionContextTask.h"
     33 #include "wtf/ThreadingPrimitives.h"
     34 
     35 namespace WebCore {
     36 
     37 // A helper class to safely dereference the callback objects held by
     38 // SQLStatement and SQLTransaction on the proper thread. The 'wrapped'
     39 // callback is dereferenced:
     40 // - by destructing the enclosing wrapper - on any thread
     41 // - by calling clear() - on any thread
     42 // - by unwrapping and then dereferencing normally - on context thread only
     43 template<typename T> class SQLCallbackWrapper {
     44 public:
     45     SQLCallbackWrapper(PassOwnPtr<T> callback, ExecutionContext* executionContext)
     46         : m_callback(callback)
     47         , m_executionContext(m_callback ? executionContext : 0)
     48     {
     49         ASSERT(!m_callback || (m_executionContext.get() && m_executionContext->isContextThread()));
     50     }
     51 
     52     ~SQLCallbackWrapper()
     53     {
     54         clear();
     55     }
     56 
     57     void clear()
     58     {
     59         ExecutionContext* context;
     60         OwnPtr<T> callback;
     61         {
     62             MutexLocker locker(m_mutex);
     63             if (!m_callback) {
     64                 ASSERT(!m_executionContext);
     65                 return;
     66             }
     67             if (m_executionContext->isContextThread()) {
     68                 m_callback.clear();
     69                 m_executionContext.clear();
     70                 return;
     71             }
     72             context = m_executionContext.release().leakRef();
     73             callback = m_callback.release();
     74         }
     75         context->postTask(SafeReleaseTask::create(callback.release()));
     76     }
     77 
     78     PassOwnPtr<T> unwrap()
     79     {
     80         MutexLocker locker(m_mutex);
     81         ASSERT(!m_callback || m_executionContext->isContextThread());
     82         m_executionContext.clear();
     83         return m_callback.release();
     84     }
     85 
     86     // Useful for optimizations only, please test the return value of unwrap to be sure.
     87     bool hasCallback() const { return m_callback; }
     88 
     89 private:
     90     class SafeReleaseTask : public ExecutionContextTask {
     91     public:
     92         static PassOwnPtr<SafeReleaseTask> create(PassOwnPtr<T> callbackToRelease)
     93         {
     94             return adoptPtr(new SafeReleaseTask(callbackToRelease));
     95         }
     96 
     97         virtual void performTask(ExecutionContext* context)
     98         {
     99             ASSERT(m_callbackToRelease && context && context->isContextThread());
    100             m_callbackToRelease.clear();
    101             context->deref();
    102         }
    103 
    104         virtual bool isCleanupTask() const { return true; }
    105 
    106     private:
    107         explicit SafeReleaseTask(PassOwnPtr<T> callbackToRelease)
    108             : m_callbackToRelease(callbackToRelease)
    109         {
    110         }
    111 
    112         OwnPtr<T> m_callbackToRelease;
    113     };
    114 
    115     Mutex m_mutex;
    116     OwnPtr<T> m_callback;
    117     RefPtr<ExecutionContext> m_executionContext;
    118 };
    119 
    120 } // namespace WebCore
    121 
    122 #endif // SQLCallbackWrapper_h
    123