/*

 * Copyright (C) 2005, 2008, 2009 Apple Inc. All rights reserved.

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Library General Public

 * License as published by the Free Software Foundation; either

 * version 2 of the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Library General Public License for more details.

 *

 * You should have received a copy of the GNU Library General Public License

 * along with this library; see the file COPYING.LIB.  If not, write to

 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,

 * Boston, MA 02110-1301, USA.

 *

 */

#ifndef JSLock_h

#define JSLock_h

#include <wtf/Assertions.h>

#include <wtf/Noncopyable.h>

namespace JSC {

    // To make it safe to use JavaScript on multiple threads, it is

    // important to lock before doing anything that allocates a

    // JavaScript data structure or that interacts with shared state

    // such as the protect count hash table. The simplest way to lock

    // is to create a local JSLock object in the scope where the lock 

    // must be held. The lock is recursive so nesting is ok. The JSLock 

    // object also acts as a convenience short-hand for running important

    // initialization routines.

    // To avoid deadlock, sometimes it is necessary to temporarily

    // release the lock. Since it is recursive you actually have to

    // release all locks held by your thread. This is safe to do if

    // you are executing code that doesn't require the lock, and you

    // reacquire the right number of locks at the end. You can do this

    // by constructing a locally scoped JSLock::DropAllLocks object. The 

    // DropAllLocks object takes care to release the JSLock only if your

    // thread acquired it to begin with.

    // For contexts other than the single shared one, implicit locking is not done,

    // but we still need to perform all the counting in order to keep debug

    // assertions working, so that clients that use the shared context don't break.

    class ExecState;

    enum JSLockBehavior { SilenceAssertionsOnly, LockForReal };

    class JSLock : public Noncopyable {

    public:

        JSLock(ExecState*);

        JSLock(JSLockBehavior lockBehavior)

            : m_lockBehavior(lockBehavior)

        {

#ifdef NDEBUG

            // Locking "not for real" is a debug-only feature.

            if (lockBehavior == SilenceAssertionsOnly)

                return;

#endif

            lock(lockBehavior);

        }

        ~JSLock()

        { 

#ifdef NDEBUG

            // Locking "not for real" is a debug-only feature.

            if (m_lockBehavior == SilenceAssertionsOnly)

                return;

#endif

            unlock(m_lockBehavior); 

        }

        static void lock(JSLockBehavior);

        static void unlock(JSLockBehavior);

        static void lock(ExecState*);

        static void unlock(ExecState*);

        static intptr_t lockCount();

        static bool currentThreadIsHoldingLock();

        JSLockBehavior m_lockBehavior;

        class DropAllLocks : public Noncopyable {

        public:

            DropAllLocks(ExecState* exec);

            DropAllLocks(JSLockBehavior);

            ~DropAllLocks();

        private:

            intptr_t m_lockCount;

            JSLockBehavior m_lockBehavior;

        };

    };

} // namespace

#endif // JSLock_h