1/*
2 * Copyright (C) 2005, 2008, 2009 Apple Inc. All rights reserved.
3 *
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Library General Public
6 * License as published by the Free Software Foundation; either
7 * version 2 of the License, or (at your option) any later version.
8 *
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Library General Public License for more details.
13 *
14 * You should have received a copy of the GNU Library General Public License
15 * along with this library; see the file COPYING.LIB. If not, write to
16 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
17 * Boston, MA 02110-1301, USA.
18 *
19 */
20
21#ifndef JSLock_h
22#define JSLock_h
23
24#include <wtf/Assertions.h>
25#include <wtf/Noncopyable.h>
26
27namespace JSC {
28
29 // To make it safe to use JavaScript on multiple threads, it is
30 // important to lock before doing anything that allocates a
31 // JavaScript data structure or that interacts with shared state
32 // such as the protect count hash table. The simplest way to lock
33 // is to create a local JSLock object in the scope where the lock
34 // must be held. The lock is recursive so nesting is ok. The JSLock
35 // object also acts as a convenience short-hand for running important
36 // initialization routines.
37
38 // To avoid deadlock, sometimes it is necessary to temporarily
39 // release the lock. Since it is recursive you actually have to
40 // release all locks held by your thread. This is safe to do if
41 // you are executing code that doesn't require the lock, and you
42 // reacquire the right number of locks at the end. You can do this
43 // by constructing a locally scoped JSLock::DropAllLocks object. The
44 // DropAllLocks object takes care to release the JSLock only if your
45 // thread acquired it to begin with.
46
47 // For contexts other than the single shared one, implicit locking is not done,
48 // but we still need to perform all the counting in order to keep debug
49 // assertions working, so that clients that use the shared context don't break.
50
51 class ExecState;
52
53 enum JSLockBehavior { SilenceAssertionsOnly, LockForReal };
54
55 class JSLock : public Noncopyable {
56 public:
57 JSLock(ExecState*);
58
59 JSLock(JSLockBehavior lockBehavior)
60 : m_lockBehavior(lockBehavior)
61 {
62#ifdef NDEBUG
63 // Locking "not for real" is a debug-only feature.
64 if (lockBehavior == SilenceAssertionsOnly)
65 return;
66#endif
67 lock(lockBehavior);
68 }
69
70 ~JSLock()
71 {
72#ifdef NDEBUG
73 // Locking "not for real" is a debug-only feature.
74 if (m_lockBehavior == SilenceAssertionsOnly)
75 return;
76#endif
77 unlock(m_lockBehavior);
78 }
79
80 static void lock(JSLockBehavior);
81 static void unlock(JSLockBehavior);
82 static void lock(ExecState*);
83 static void unlock(ExecState*);
84
85 static intptr_t lockCount();
86 static bool currentThreadIsHoldingLock();
87
88 JSLockBehavior m_lockBehavior;
89
90 class DropAllLocks : public Noncopyable {
91 public:
92 DropAllLocks(ExecState* exec);
93 DropAllLocks(JSLockBehavior);
94 ~DropAllLocks();
95
96 private:
97 intptr_t m_lockCount;
98 JSLockBehavior m_lockBehavior;
99 };
100 };
101
102} // namespace
103
104#endif // JSLock_h
105

source code of qtscript/src/3rdparty/javascriptcore/JavaScriptCore/runtime/JSLock.h