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/*
* 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;
class JSGlobalData;
enum JSLockBehavior { SilenceAssertionsOnly, LockForReal };
class JSLock {
WTF_MAKE_NONCOPYABLE(JSLock);
public:
JSLock(ExecState*);
JSLock(JSGlobalData*);
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 {
WTF_MAKE_NONCOPYABLE(DropAllLocks);
public:
DropAllLocks(ExecState* exec);
DropAllLocks(JSLockBehavior);
~DropAllLocks();
private:
intptr_t m_lockCount;
JSLockBehavior m_lockBehavior;
};
};
} // namespace
#endif // JSLock_h