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 | |
27 | namespace 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 | |