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
37namespace 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
45template<typename T> class SQLCallbackWrapper {
46public:
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
91private:
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