2 * Copyright (C) 2005, 2008, 2009 Apple Inc. All rights reserved.
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.
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.
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.
24 #include <wtf/Assertions.h>
25 #include <wtf/Noncopyable.h>
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.
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.
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.
54 enum JSLockBehavior { SilenceAssertionsOnly, LockForReal };
57 WTF_MAKE_NONCOPYABLE(JSLock);
60 JSLock(JSGlobalData*);
62 JSLock(JSLockBehavior lockBehavior)
63 : m_lockBehavior(lockBehavior)
66 // Locking "not for real" is a debug-only feature.
67 if (lockBehavior == SilenceAssertionsOnly)
76 // Locking "not for real" is a debug-only feature.
77 if (m_lockBehavior == SilenceAssertionsOnly)
80 unlock(m_lockBehavior);
83 static void lock(JSLockBehavior);
84 static void unlock(JSLockBehavior);
85 static void lock(ExecState*);
86 static void unlock(ExecState*);
88 static intptr_t lockCount();
89 static bool currentThreadIsHoldingLock();
91 JSLockBehavior m_lockBehavior;
94 WTF_MAKE_NONCOPYABLE(DropAllLocks);
96 DropAllLocks(ExecState* exec);
97 DropAllLocks(JSLockBehavior);
101 intptr_t m_lockCount;
102 JSLockBehavior m_lockBehavior;