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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 #if ENABLE(DATABASE)
     32 
     33 #include "CrossThreadTask.h"
     34 #include "ScriptExecutionContext.h"
     35 #include <wtf/ThreadingPrimitives.h>
     36 
     37 namespace WebCore {
     38 
     39 // A helper class to safely dereference the callback objects held by
     40 // SQLStatement and SQLTransaction on the proper thread. The 'wrapped'
     41 // callback is dereferenced:
     42 // - by destructing the enclosing wrapper - on any thread
     43 // - by calling clear() - on any thread
     44 // - by unwrapping and then dereferencing normally - on context thread only
     45 template<typename T> class SQLCallbackWrapper {
     46 public:
     47     SQLCallbackWrapper(PassRefPtr<T> callback, ScriptExecutionContext* scriptExecutionContext)
     48         : m_callback(callback)
     49         , m_scriptExecutionContext(m_callback ? scriptExecutionContext : 0)
     50     {
     51         ASSERT(!m_callback || (m_scriptExecutionContext.get() && m_scriptExecutionContext->isContextThread()));
     52     }
     53 
     54     ~SQLCallbackWrapper()
     55     {
     56         clear();
     57     }
     58 
     59     void clear()
     60     {
     61         ScriptExecutionContext* context;
     62         T* callback;
     63         {
     64             MutexLocker locker(m_mutex);
     65             if (!m_callback) {
     66                 ASSERT(!m_scriptExecutionContext);
     67                 return;
     68             }
     69             if (m_scriptExecutionContext->isContextThread()) {
     70                 m_callback = 0;
     71                 m_scriptExecutionContext = 0;
     72                 return;
     73             }
     74             context = m_scriptExecutionContext.release().leakRef();
     75             callback = m_callback.release().leakRef();
     76         }
     77         context->postTask(createCallbackTask(&safeRelease, callback));
     78     }
     79 
     80     PassRefPtr<T> unwrap()
     81     {
     82         MutexLocker locker(m_mutex);
     83         ASSERT(!m_callback || m_scriptExecutionContext->isContextThread());
     84         m_scriptExecutionContext = 0;
     85         return m_callback.release();
     86     }
     87 
     88     // Useful for optimizations only, please test the return value of unwrap to be sure.
     89     bool hasCallback() const { return m_callback; }
     90 
     91 private:
     92     static void safeRelease(ScriptExecutionContext* context, T* callback)
     93     {
     94         ASSERT(callback && context && context->isContextThread());
     95         callback->deref();
     96         context->deref();
     97     }
     98 
     99     Mutex m_mutex;
    100     RefPtr<T> m_callback;
    101     RefPtr<ScriptExecutionContext> m_scriptExecutionContext;
    102 };
    103 
    104 } // namespace WebCore
    105 
    106 #endif // ENABLE(DATABASE)
    107 
    108 #endif // SQLCallbackWrapper_h
    109