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
35namespace 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
43template<typename T> class SQLCallbackWrapper {
44public:
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
89private:
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