blob: 5e3d12c92935930489fc0946e9a48a8af253f5e0 [file] [log] [blame]
/*
* Copyright (C) 2005, 2008 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 NU
* 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
*
*/
#include "config.h"
#include "JSLock.h"
#include "Heap.h"
#include "CallFrame.h"
#include "JSGlobalObject.h"
#include "JSObject.h"
#if USE(PTHREADS)
#include <pthread.h>
#endif
namespace JSC {
Mutex* GlobalJSLock::s_sharedInstanceLock = 0;
GlobalJSLock::GlobalJSLock()
{
s_sharedInstanceLock->lock();
}
GlobalJSLock::~GlobalJSLock()
{
s_sharedInstanceLock->unlock();
}
void GlobalJSLock::initialize()
{
s_sharedInstanceLock = new Mutex();
}
JSLockHolder::JSLockHolder(ExecState* exec)
: m_globalData(&exec->globalData())
{
m_globalData->apiLock().lock();
}
JSLockHolder::JSLockHolder(JSGlobalData* globalData)
: m_globalData(globalData)
{
m_globalData->apiLock().lock();
}
JSLockHolder::JSLockHolder(JSGlobalData& globalData)
: m_globalData(&globalData)
{
m_globalData->apiLock().lock();
}
JSLockHolder::~JSLockHolder()
{
m_globalData->apiLock().unlock();
}
JSLock::JSLock()
: m_ownerThread(0)
, m_lockCount(0)
, m_lockDropDepth(0)
{
m_spinLock.Init();
}
JSLock::~JSLock()
{
}
void JSLock::lock()
{
ThreadIdentifier currentThread = WTF::currentThread();
{
SpinLockHolder holder(&m_spinLock);
if (m_ownerThread == currentThread && m_lockCount) {
m_lockCount++;
return;
}
}
m_lock.lock();
{
SpinLockHolder holder(&m_spinLock);
m_ownerThread = currentThread;
ASSERT(!m_lockCount);
m_lockCount = 1;
}
}
void JSLock::unlock()
{
ASSERT(currentThreadIsHoldingLock());
SpinLockHolder holder(&m_spinLock);
m_lockCount--;
if (!m_lockCount)
m_lock.unlock();
}
void JSLock::lock(ExecState* exec)
{
exec->globalData().apiLock().lock();
}
void JSLock::unlock(ExecState* exec)
{
exec->globalData().apiLock().unlock();
}
bool JSLock::currentThreadIsHoldingLock()
{
return m_lockCount && m_ownerThread == WTF::currentThread();
}
// This is fairly nasty. We allow multiple threads to run on the same
// context, and we do not require any locking semantics in doing so -
// clients of the API may simply use the context from multiple threads
// concurently, and assume this will work. In order to make this work,
// We lock the context when a thread enters, and unlock it when it leaves.
// However we do not only unlock when the thread returns from its
// entry point (evaluate script or call function), we also unlock the
// context if the thread leaves JSC by making a call out to an external
// function through a callback.
//
// All threads using the context share the same JS stack (the JSStack).
// Whenever a thread calls into JSC it starts using the JSStack from the
// previous 'high water mark' - the maximum point the stack has ever grown to
// (returned by JSStack::end()). So if a first thread calls out to a
// callback, and a second thread enters JSC, then also exits by calling out
// to a callback, we can be left with stackframes from both threads in the
// JSStack. As such, a problem may occur should the first thread's
// callback complete first, and attempt to return to JSC. Were we to allow
// this to happen, and were its stack to grow further, then it may potentially
// write over the second thread's call frames.
//
// To avoid JS stack corruption we enforce a policy of only ever allowing two
// threads to use a JS context concurrently, and only allowing the second of
// these threads to execute until it has completed and fully returned from its
// outermost call into JSC. We enforce this policy using 'lockDropDepth'. The
// first time a thread exits it will call DropAllLocks - which will do as expected
// and drop locks allowing another thread to enter. Should another thread, or the
// same thread again, enter JSC (through evaluate script or call function), and exit
// again through a callback, then the locks will not be dropped when DropAllLocks
// is called (since lockDropDepth is non-zero). Since this thread is still holding
// the locks, only it will be able to re-enter JSC (either be returning from the
// callback, or by re-entering through another call to evaulate script or call
// function).
//
// This policy is slightly more restricive than it needs to be for correctness -
// we could validly allow futher entries into JSC from other threads, we only
// need ensure that callbacks return in the reverse chronological order of the
// order in which they were made - though implementing the less restrictive policy
// would likely increase complexity and overhead.
//
// This function returns the number of locks that were dropped.
unsigned JSLock::dropAllLocks()
{
if (m_lockDropDepth++)
return 0;
return dropAllLocksUnconditionally();
}
unsigned JSLock::dropAllLocksUnconditionally()
{
unsigned lockCount = m_lockCount;
for (unsigned i = 0; i < lockCount; i++)
unlock();
return lockCount;
}
void JSLock::grabAllLocks(unsigned lockCount)
{
for (unsigned i = 0; i < lockCount; i++)
lock();
m_lockDropDepth--;
}
JSLock::DropAllLocks::DropAllLocks(ExecState* exec)
: m_lockCount(0)
, m_globalData(&exec->globalData())
{
m_lockCount = m_globalData->apiLock().dropAllLocks();
}
JSLock::DropAllLocks::DropAllLocks(JSGlobalData* globalData)
: m_lockCount(0)
, m_globalData(globalData)
{
m_lockCount = m_globalData->apiLock().dropAllLocks();
}
JSLock::DropAllLocks::~DropAllLocks()
{
m_globalData->apiLock().grabAllLocks(m_lockCount);
}
} // namespace JSC