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