1/*
2 * Copyright (C) 2008 Apple 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 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 *
25 */
26
27#ifndef ActiveDOMObject_h
28#define ActiveDOMObject_h
29
30#include "ContextDestructionObserver.h"
31#include <wtf/Assertions.h>
32#include <wtf/Forward.h>
33
34namespace WebCore {
35
36class ActiveDOMObject : public ContextDestructionObserver {
37public:
38    explicit ActiveDOMObject(ScriptExecutionContext*);
39
40    // The suspendIfNeeded must be called exactly once after object construction to update
41    // the suspended state to match that of the ScriptExecutionContext.
42    void suspendIfNeeded();
43    void assertSuspendIfNeededWasCalled() const;
44
45    virtual bool hasPendingActivity() const;
46
47    // The canSuspend function is used by the caller if there is a choice between suspending
48    // and stopping. For example, a page won't be suspended and placed in the back/forward
49    // cache if it contains any objects that cannot be suspended.
50
51    // However, the suspend function will sometimes be called even if canSuspend returns false.
52    // That happens in step-by-step JS debugging for example - in this case it would be incorrect
53    // to stop the object. Exact semantics of suspend is up to the object in cases like that.
54
55    enum ReasonForSuspension {
56        JavaScriptDebuggerPaused,
57        WillDeferLoading,
58        DocumentWillBecomeInactive,
59        PageWillBeSuspended,
60        DocumentWillBePaused
61    };
62
63    // These three functions must not have a side effect of creating or destroying
64    // any ActiveDOMObject. That means they must not result in calls to arbitrary JavaScript.
65    virtual bool canSuspend() const;
66    virtual void suspend(ReasonForSuspension);
67    virtual void resume();
68
69    // This function must not have a side effect of creating an ActiveDOMObject.
70    // That means it must not result in calls to arbitrary JavaScript.
71    // It can, however, have a side effect of deleting an ActiveDOMObject.
72    virtual void stop();
73
74    template<class T> void setPendingActivity(T* thisObject)
75    {
76        ASSERT(thisObject == this);
77        thisObject->ref();
78        ++m_pendingActivityCount;
79    }
80
81    template<class T> void unsetPendingActivity(T* thisObject)
82    {
83        ASSERT(m_pendingActivityCount > 0);
84        --m_pendingActivityCount;
85        thisObject->deref();
86    }
87
88protected:
89    virtual ~ActiveDOMObject();
90
91private:
92    unsigned m_pendingActivityCount;
93#if !ASSERT_DISABLED
94    bool m_suspendIfNeededWasCalled;
95#endif
96};
97
98#if ASSERT_DISABLED
99
100inline void ActiveDOMObject::assertSuspendIfNeededWasCalled() const
101{
102}
103
104#endif
105
106} // namespace WebCore
107
108#endif // ActiveDOMObject_h
109