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