Home | History | Annotate | Download | only in webdatabase 
      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/ScriptExecutionContext.h"
     32 #include "wtf/ThreadingPrimitives.h"
     33 
     34 namespace WebCore {
     35 
     36 // A helper class to safely dereference the callback objects held by
     37 // SQLStatement and SQLTransaction on the proper thread. The 'wrapped'
     38 // callback is dereferenced:
     39 // - by destructing the enclosing wrapper - on any thread
     40 // - by calling clear() - on any thread
     41 // - by unwrapping and then dereferencing normally - on context thread only
     42 template<typename T> class SQLCallbackWrapper {
     43 public:
     44     SQLCallbackWrapper(PassRefPtr<T> callback, ScriptExecutionContext* scriptExecutionContext)
     45         : m_callback(callback)
     46         , m_scriptExecutionContext(m_callback ? scriptExecutionContext : 0)
     47     {
     48         ASSERT(!m_callback || (m_scriptExecutionContext.get() && m_scriptExecutionContext->isContextThread()));
     49     }
     50 
     51     ~SQLCallbackWrapper()
     52     {
     53         clear();
     54     }
     55 
     56     void clear()
     57     {
     58         ScriptExecutionContext* context;
     59         T* callback;
     60         {
     61             MutexLocker locker(m_mutex);
     62             if (!m_callback) {
     63                 ASSERT(!m_scriptExecutionContext);
     64                 return;
     65             }
     66             if (m_scriptExecutionContext->isContextThread()) {
     67                 m_callback = 0;
     68                 m_scriptExecutionContext = 0;
     69                 return;
     70             }
     71             context = m_scriptExecutionContext.release().leakRef();
     72             callback = m_callback.release().leakRef();
     73         }
     74         context->postTask(SafeReleaseTask::create(callback));
     75     }
     76 
     77     PassRefPtr<T> unwrap()
     78     {
     79         MutexLocker locker(m_mutex);
     80         ASSERT(!m_callback || m_scriptExecutionContext->isContextThread());
     81         m_scriptExecutionContext = 0;
     82         return m_callback.release();
     83     }
     84 
     85     // Useful for optimizations only, please test the return value of unwrap to be sure.
     86     bool hasCallback() const { return m_callback; }
     87 
     88 private:
     89     class SafeReleaseTask : public ScriptExecutionContext::Task {
     90     public:
     91         static PassOwnPtr<SafeReleaseTask> create(T* callbackToRelease)
     92         {
     93             return adoptPtr(new SafeReleaseTask(callbackToRelease));
     94         }
     95 
     96         virtual void performTask(ScriptExecutionContext* context)
     97         {
     98             ASSERT(m_callbackToRelease && context && context->isContextThread());
     99             m_callbackToRelease->deref();
    100             context->deref();
    101         }
    102 
    103         virtual bool isCleanupTask() const { return true; }
    104 
    105     private:
    106         explicit SafeReleaseTask(T* callbackToRelease)
    107             : m_callbackToRelease(callbackToRelease)
    108         {
    109         }
    110 
    111         T* m_callbackToRelease;
    112     };
    113 
    114     Mutex m_mutex;
    115     RefPtr<T> m_callback;
    116     RefPtr<ScriptExecutionContext> m_scriptExecutionContext;
    117 };
    118 
    119 } // namespace WebCore
    120 
    121 #endif // SQLCallbackWrapper_h
    122