WorkerOrWorkletThread.cpp   [plain text]

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#include "config.h"
#include "WorkerOrWorkletThread.h"

#include "ThreadGlobalData.h"
#include "WorkerOrWorkletGlobalScope.h"
#include "WorkerOrWorkletScriptController.h"

#if PLATFORM(IOS_FAMILY)
#include "FloatingPointEnvironment.h"
#endif

#if USE(GLIB)
#include <wtf/glib/GRefPtr.h>
#endif

namespace WebCore {

Lock& WorkerOrWorkletThread::workerOrWorkletThreadsLock()
{
    static Lock mutex;
    return mutex;
}

HashSet<WorkerOrWorkletThread*>& WorkerOrWorkletThread::workerOrWorkletThreads()
{
    ASSERT(workerOrWorkletThreadsLock().isHeld());
    static NeverDestroyed<HashSet<WorkerOrWorkletThread*>> workerOrWorkletThreads;
    return workerOrWorkletThreads;
}

WorkerOrWorkletThread::WorkerOrWorkletThread(const String& identifier)
    : m_identifier(identifier)
{
    auto locker = holdLock(workerOrWorkletThreadsLock());
    workerOrWorkletThreads().add(this);
}

WorkerOrWorkletThread::~WorkerOrWorkletThread()
{
    auto locker = holdLock(workerOrWorkletThreadsLock());
    ASSERT(workerOrWorkletThreads().contains(this));
    workerOrWorkletThreads().remove(this);
}

void WorkerOrWorkletThread::startRunningDebuggerTasks()
{
    ASSERT(!m_pausedForDebugger);
    m_pausedForDebugger = true;

    MessageQueueWaitResult result;
    do {
        result = m_runLoop.runInDebuggerMode(*m_globalScope);
    } while (result != MessageQueueTerminated && m_pausedForDebugger);
}

void WorkerOrWorkletThread::stopRunningDebuggerTasks()
{
    m_pausedForDebugger = false;
}

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

void WorkerOrWorkletThread::workerOrWorkletThread()
{
    auto protectedThis = makeRef(*this);

    // Propagate the mainThread's fenv to workers.
#if PLATFORM(IOS_FAMILY)
    FloatingPointEnvironment::singleton().propagateMainThreadEnvironment();
#endif

#if USE(GLIB)
    GRefPtr<GMainContext> mainContext = adoptGRef(g_main_context_new());
    g_main_context_push_thread_default(mainContext.get());
#endif

    WorkerOrWorkletScriptController* scriptController;
    {
        // Mutex protection is necessary to ensure that we don't change m_globalScope
        // while WorkerThread::stop() is accessing it. Note that WorkerThread::stop() can
        // be called before we've finished creating the WorkerGlobalScope.
        auto locker = holdLock(m_threadCreationAndGlobalScopeLock);
        m_globalScope = createGlobalScope();

        scriptController = m_globalScope->script();

        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().
            scriptController->scheduleExecutionTermination();
            scriptController->forbidExecution();
        }
    }

    if (shouldWaitForWebInspectorOnStartup()) {
        startRunningDebuggerTasks();

        // If the worker was somehow terminated while processing debugger commands.
        if (m_runLoop.terminated())
            scriptController->forbidExecution();
    }

    String exceptionMessage;
    evaluateScriptIfNecessary(exceptionMessage);

    callOnMainThread([evaluateCallback = WTFMove(m_evaluateCallback), message = exceptionMessage.isolatedCopy()] {
        if (evaluateCallback)
            evaluateCallback(message);
    });

    runEventLoop();

#if USE(GLIB)
    g_main_context_pop_thread_default(mainContext.get());
#endif

    RefPtr<Thread> protector = m_thread;

    ASSERT(m_globalScope->hasOneRef());

    RefPtr<WorkerOrWorkletGlobalScope> workerGlobalScopeToDelete;
    {
        // Mutex protection is necessary to ensure that we don't change m_globalScope
        // while WorkerThread::stop is accessing it.
        auto locker = holdLock(m_threadCreationAndGlobalScopeLock);

        // Delay the destruction of the WorkerGlobalScope context until after we've unlocked the
        // m_threadCreationAndWorkerGlobalScopeMutex. This is needed because destructing the
        // context will trigger the main thread to race against us to delete the WorkerThread
        // object, and the WorkerThread object owns the mutex we need to unlock after this.
        workerGlobalScopeToDelete = std::exchange(m_globalScope, nullptr);

        if (m_stoppedCallback)
            callOnMainThread(WTFMove(m_stoppedCallback));
    }

    // 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.
    workerGlobalScopeToDelete = nullptr;

    // Clean up WebCore::ThreadGlobalData before WTF::Thread goes away!
    threadGlobalData().destroy();

    // Send the last WorkerThread Ref to be Deref'ed on the main thread.
    callOnMainThread([protectedThis = WTFMove(protectedThis)] { });

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

void WorkerOrWorkletThread::start(WTF::Function<void(const String&)>&& evaluateCallback)
{
    // Mutex protection is necessary to ensure that m_thread is initialized when the thread starts.
    auto locker = holdLock(m_threadCreationAndGlobalScopeLock);

    if (m_thread)
        return;

    m_evaluateCallback = WTFMove(evaluateCallback);

    auto thread = createThread();

    // Force the Thread object to be initialized fully before storing it to m_thread (and becoming visible to other threads).
    WTF::storeStoreFence();

    m_thread = WTFMove(thread);
}

void WorkerOrWorkletThread::stop(Function<void()>&& stoppedCallback)
{
    // Mutex protection is necessary to ensure that m_workerGlobalScope isn't changed by
    // WorkerThread::workerThread() while we're accessing it. Note also that stop() can
    // be called before m_workerGlobalScope is fully created.
    auto locker = tryHoldLock(m_threadCreationAndGlobalScopeLock);
    if (!locker) {
        // The thread is still starting, spin the runloop and try again to avoid deadlocks if the worker thread
        // needs to interact with the main thread during startup.
        callOnMainThread([this, stoppedCallback = WTFMove(stoppedCallback)]() mutable {
            stop(WTFMove(stoppedCallback));
        });
        return;
    }

    // If the thread is suspended, resume it now so that we can dispatch the cleanup tasks below.
    if (m_isSuspended)
        resume();

    ASSERT(!m_stoppedCallback);
    m_stoppedCallback = WTFMove(stoppedCallback);

    // 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 (globalScope()) {
        globalScope()->script()->scheduleExecutionTermination();

        m_runLoop.postTaskAndTerminate({ ScriptExecutionContext::Task::CleanupTask, [] (ScriptExecutionContext& context ) {
            auto& globalScope = downcast<WorkerOrWorkletGlobalScope>(context);

            globalScope.prepareForDestruction();

            // Stick a shutdown command at the end of the queue, so that we deal
            // with all the cleanup tasks the databases post first.
            globalScope.postTask({ ScriptExecutionContext::Task::CleanupTask, [] (ScriptExecutionContext& context) {
                auto& globalScope = downcast<WorkerOrWorkletGlobalScope>(context);
                // It's not safe to call clearScript until all the cleanup tasks posted by functions initiated by WorkerThreadShutdownStartTask have completed.
                globalScope.clearScript();
            } });

        } });
        return;
    }
    m_runLoop.terminate();
}

void WorkerOrWorkletThread::suspend()
{
    m_isSuspended = true;
    m_runLoop.postTask([&](ScriptExecutionContext&) {
        if (globalScope())
            globalScope()->suspend();

        m_suspensionSemaphore.wait();

        if (globalScope())
            globalScope()->resume();
    });
}

void WorkerOrWorkletThread::resume()
{
    ASSERT(m_isSuspended);
    m_isSuspended = false;
    m_suspensionSemaphore.signal();
}

void WorkerOrWorkletThread::releaseFastMallocFreeMemoryInAllThreads()
{
    auto locker = holdLock(workerOrWorkletThreadsLock());
    for (auto* workerOrWorkletThread : workerOrWorkletThreads()) {
        workerOrWorkletThread->runLoop().postTask([] (ScriptExecutionContext&) {
            WTF::releaseFastMallocFreeMemory();
        });
    }
}

} // namespace WebCore