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 JSLock(JSLockBehavior lockBehavior)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 ~JSLock()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