root/Source/core/workers/WorkerThread.cpp

DEFINITIONS

1. threadSetMutex
2. workerThreads
3. workerThreadCount
4. m_shutdownEvent
5. start
6. workerThreadStart
7. workerThread
8. runEventLoop
9. create
10. performTask
11. isCleanupTask
12. create
13. performTask
14. isCleanupTask
15. stop
16. isCurrentThread
17. performTask
18. releaseFastMallocFreeMemoryInAllThreads

/*
 * Copyright (C) 2008 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 COMPUTER, INC. ``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 COMPUTER, INC. OR
 * 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 "core/workers/WorkerThread.h"

#include "bindings/v8/ScriptSourceCode.h"
#include "core/inspector/InspectorInstrumentation.h"
#include "core/workers/DedicatedWorkerGlobalScope.h"
#include "core/workers/WorkerClients.h"
#include "core/workers/WorkerReportingProxy.h"
#include "core/workers/WorkerThreadStartupData.h"
#include "platform/PlatformThreadData.h"
#include "platform/heap/ThreadState.h"
#include "platform/weborigin/KURL.h"
#include "public/platform/Platform.h"
#include "public/platform/WebWaitableEvent.h"
#include "public/platform/WebWorkerRunLoop.h"
#include "wtf/Noncopyable.h"
#include "wtf/text/WTFString.h"

#include <utility>

namespace WebCore {

static Mutex& threadSetMutex()
{
    AtomicallyInitializedStatic(Mutex&, mutex = *new Mutex);
    return mutex;
}

static HashSet<WorkerThread*>& workerThreads()
{
    DEFINE_STATIC_LOCAL(HashSet<WorkerThread*>, threads, ());
    return threads;
}

unsigned WorkerThread::workerThreadCount()
{
    MutexLocker lock(threadSetMutex());
    return workerThreads().size();
}

WorkerThread::WorkerThread(WorkerLoaderProxy& workerLoaderProxy, WorkerReportingProxy& workerReportingProxy, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData> startupData)
    : m_threadID(0)
    , m_workerLoaderProxy(workerLoaderProxy)
    , m_workerReportingProxy(workerReportingProxy)
    , m_startupData(startupData)
    , m_notificationClient(0)
    , m_shutdownEvent(adoptPtr(blink::Platform::current()->createWaitableEvent()))
{
    MutexLocker lock(threadSetMutex());
    workerThreads().add(this);
}

WorkerThread::~WorkerThread()
{
    MutexLocker lock(threadSetMutex());
    ASSERT(workerThreads().contains(this));
    workerThreads().remove(this);
}

bool WorkerThread::start()
{
    // Mutex protection is necessary to ensure that m_threadID is initialized when the thread starts.
    MutexLocker lock(m_threadCreationMutex);

    if (m_threadID)
        return true;

    m_threadID = createThread(WorkerThread::workerThreadStart, this, "WebCore: Worker");

    return m_threadID;
}

void WorkerThread::workerThreadStart(void* thread)
{
    static_cast<WorkerThread*>(thread)->workerThread();
}

void WorkerThread::workerThread()
{
    KURL scriptURL = m_startupData->m_scriptURL;
    String sourceCode = m_startupData->m_sourceCode;
    WorkerThreadStartMode startMode = m_startupData->m_startMode;

    {
        MutexLocker lock(m_threadCreationMutex);
        ThreadState::attach();
        m_workerGlobalScope = createWorkerGlobalScope(m_startupData.release());
        m_runLoop.setWorkerGlobalScope(workerGlobalScope());

        if (m_runLoop.terminated()) {
            // The worker was terminated before the thread had a chance to run. Since the context didn't exist yet,
            // forbidExecution() couldn't be called from stop().
            m_workerGlobalScope->script()->forbidExecution();
        }
    }
    // The corresponding call to didStopWorkerRunLoop is in
    // ~WorkerScriptController.
    blink::Platform::current()->didStartWorkerRunLoop(blink::WebWorkerRunLoop(&m_runLoop));

    // Notify proxy that a new WorkerGlobalScope has been created and started.
    m_workerReportingProxy.workerGlobalScopeStarted(m_workerGlobalScope.get());

    WorkerScriptController* script = m_workerGlobalScope->script();
    InspectorInstrumentation::willEvaluateWorkerScript(workerGlobalScope(), startMode);
    script->evaluate(ScriptSourceCode(sourceCode, scriptURL));

    runEventLoop();

    ThreadIdentifier threadID = m_threadID;

    // The below assignment will destroy the context, which will in turn notify messaging proxy.
    // We cannot let any objects survive past thread exit, because no other thread will run GC or otherwise destroy them.
    // If Oilpan is enabled, we detach of the context/global scope, with the final heap cleanup below sweeping it out.
#if ENABLE(OILPAN)
    m_workerGlobalScope->dispose();
#else
    ASSERT(m_workerGlobalScope->hasOneRef());
#endif
    m_workerGlobalScope = nullptr;

    // Detach the ThreadState, cleaning out the thread's heap by
    // performing a final GC. The cleanup operation will at the end
    // assert that the heap is empty. If the heap does not become
    // empty, there are still pointers into the heap and those
    // pointers will be dangling after thread termination because we
    // are destroying the heap. It is important to detach while the
    // thread is still valid. In particular, finalizers for objects in
    // the heap for this thread will need to access thread local data.
    ThreadState::detach();

    // Notify the proxy that the WorkerGlobalScope has been disposed of.
    // This can free this thread object, hence it must not be touched afterwards.
    workerReportingProxy().workerGlobalScopeDestroyed();

    // Clean up PlatformThreadData before WTF::WTFThreadData goes away!
    PlatformThreadData::current().destroy();

    // The thread object may be already destroyed from notification now, don't try to access "this".
    detachThread(threadID);
}

void WorkerThread::runEventLoop()
{
    // Does not return until terminated.
    m_runLoop.run();
}

class WorkerThreadShutdownFinishTask : public ExecutionContextTask {
public:
    static PassOwnPtr<WorkerThreadShutdownFinishTask> create()
    {
        return adoptPtr(new WorkerThreadShutdownFinishTask());
    }

    virtual void performTask(ExecutionContext *context)
    {
        WorkerGlobalScope* workerGlobalScope = toWorkerGlobalScope(context);
        workerGlobalScope->clearInspector();
        // It's not safe to call clearScript until all the cleanup tasks posted by functions initiated by WorkerThreadShutdownStartTask have completed.
        workerGlobalScope->clearScript();
    }

    virtual bool isCleanupTask() const { return true; }
};

class WorkerThreadShutdownStartTask : public ExecutionContextTask {
public:
    static PassOwnPtr<WorkerThreadShutdownStartTask> create()
    {
        return adoptPtr(new WorkerThreadShutdownStartTask());
    }

    virtual void performTask(ExecutionContext *context)
    {
        WorkerGlobalScope* workerGlobalScope = toWorkerGlobalScope(context);

        workerGlobalScope->stopActiveDOMObjects();

        // Event listeners would keep DOMWrapperWorld objects alive for too long. Also, they have references to JS objects,
        // which become dangling once Heap is destroyed.
        workerGlobalScope->removeAllEventListeners();

        // Stick a shutdown command at the end of the queue, so that we deal
        // with all the cleanup tasks the databases post first.
        workerGlobalScope->postTask(WorkerThreadShutdownFinishTask::create());
    }

    virtual bool isCleanupTask() const { return true; }
};

void WorkerThread::stop()
{
    // Prevent the deadlock between GC and an attempt to stop a thread.
    ThreadState::SafePointScope safePointScope(ThreadState::HeapPointersOnStack);

    // Mutex protection is necessary because stop() can be called before the context is fully created.
    MutexLocker lock(m_threadCreationMutex);

    // Signal the thread to notify that the thread's stopping.
    if (m_shutdownEvent)
        m_shutdownEvent->signal();

    // Ensure that tasks are being handled by thread event loop. If script execution weren't forbidden, a while(1) loop in JS could keep the thread alive forever.
    if (m_workerGlobalScope) {
        m_workerGlobalScope->script()->scheduleExecutionTermination();
        m_workerGlobalScope->willStopActiveDOMObjects();
        m_runLoop.postTaskAndTerminate(WorkerThreadShutdownStartTask::create());
        return;
    }
    m_runLoop.terminate();
}

bool WorkerThread::isCurrentThread() const
{
    return m_threadID == currentThread();
}

class ReleaseFastMallocFreeMemoryTask : public ExecutionContextTask {
    virtual void performTask(ExecutionContext*) OVERRIDE { WTF::releaseFastMallocFreeMemory(); }
};

void WorkerThread::releaseFastMallocFreeMemoryInAllThreads()
{
    MutexLocker lock(threadSetMutex());
    HashSet<WorkerThread*>& threads = workerThreads();
    HashSet<WorkerThread*>::iterator end = threads.end();
    for (HashSet<WorkerThread*>::iterator it = threads.begin(); it != end; ++it)
        (*it)->runLoop().postTask(adoptPtr(new ReleaseFastMallocFreeMemoryTask));
}

} // namespace WebCore