runtime/JSLock.h

   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