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/*
* Copyright (C) 2010 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include <wtf/RunLoop.h>
#include <wtf/NeverDestroyed.h>
#include <wtf/StdLibExtras.h>
#include <wtf/ThreadSpecific.h>
namespace WTF {
static RunLoop* s_mainRunLoop;
#if USE(WEB_THREAD)
static RunLoop* s_webRunLoop;
#endif
// Helper class for ThreadSpecificData.
class RunLoop::Holder {
WTF_MAKE_FAST_ALLOCATED;
public:
Holder()
: m_runLoop(adoptRef(*new RunLoop))
{
}
RunLoop& runLoop() { return m_runLoop; }
private:
Ref<RunLoop> m_runLoop;
};
void RunLoop::initializeMain()
{
RELEASE_ASSERT(!s_mainRunLoop);
s_mainRunLoop = &RunLoop::current();
}
RunLoop& RunLoop::current()
{
static NeverDestroyed<ThreadSpecific<Holder>> runLoopHolder;
return runLoopHolder.get()->runLoop();
}
RunLoop& RunLoop::main()
{
ASSERT(s_mainRunLoop);
return *s_mainRunLoop;
}
#if USE(WEB_THREAD)
void RunLoop::initializeWeb()
{
RELEASE_ASSERT(!s_webRunLoop);
s_webRunLoop = &RunLoop::current();
}
RunLoop& RunLoop::web()
{
ASSERT(s_webRunLoop);
return *s_webRunLoop;
}
RunLoop* RunLoop::webIfExists()
{
return s_webRunLoop;
}
#endif
bool RunLoop::isMain()
{
ASSERT(s_mainRunLoop);
return s_mainRunLoop == &RunLoop::current();
}
void RunLoop::performWork()
{
// It is important to handle the functions in the queue one at a time because while inside one of these
// functions we might re-enter RunLoop::performWork() and we need to be able to pick up where we left off.
// See http://webkit.org/b/89590 for more discussion.
// One possible scenario when handling the function queue is as follows:
// - RunLoop::performWork() is invoked with 1 function on the queue
// - Handling that function results in 1 more function being enqueued
// - Handling that one results in yet another being enqueued
// - And so on
//
// In this situation one invocation of performWork() never returns so all other event sources are blocked.
// By only handling up to the number of functions that were in the queue when performWork() is called
// we guarantee to occasionally return from the run loop so other event sources will be allowed to spin.
size_t functionsToHandle = 1;
bool didSuspendFunctions = false;
for (size_t functionsHandled = 0; functionsHandled < functionsToHandle; ++functionsHandled) {
Function<void ()> function;
{
auto locker = holdLock(m_functionQueueLock);
// Even if we start off with N functions to handle and we've only handled less than N functions, the queue
// still might be empty because those functions might have been handled in an inner RunLoop::performWork().
// In that case we should bail here.
if (m_functionQueue.isEmpty())
break;
if (m_isFunctionDispatchSuspended) {
didSuspendFunctions = true;
break;
}
if (!functionsHandled)
functionsToHandle = m_functionQueue.size();
function = m_functionQueue.takeFirst();
}
function();
}
// Suspend only for a single cycle.
m_isFunctionDispatchSuspended = false;
m_hasSuspendedFunctions = didSuspendFunctions;
if (m_hasSuspendedFunctions)
wakeUp();
}
void RunLoop::dispatch(Function<void ()>&& function)
{
{
auto locker = holdLock(m_functionQueueLock);
m_functionQueue.append(WTFMove(function));
}
wakeUp();
}
void RunLoop::suspendFunctionDispatchForCurrentCycle()
{
// Don't suspend if there are already suspended functions to avoid unexecuted function pile-up.
if (m_isFunctionDispatchSuspended || m_hasSuspendedFunctions)
return;
m_isFunctionDispatchSuspended = true;
// Wake up (even if there is nothing to do) to disable suspension.
wakeUp();
}
} // namespace WTF