android_external_webkit/JavaScriptCore/runtime/JSLock.h at froyo · Y6b/android_external_webkit · GitHub

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* 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

android_external_webkit/JavaScriptCore/runtime/JSLock.h at froyo · Y6b/android_external_webkit · GitHub

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