src/libANGLE/WorkerThread.cpp

//
// Copyright 2016 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// WorkerThread:
//   Task running thread for ANGLE, similar to a TaskRunner in Chromium.
//   Might be implemented differently depending on platform.
//

#include "libANGLE/WorkerThread.h"

#include "libANGLE/trace.h"

#if (ANGLE_DELEGATE_WORKERS == ANGLE_ENABLED) || (ANGLE_STD_ASYNC_WORKERS == ANGLE_ENABLED)
#    include <condition_variable>
#    include <future>
#    include <mutex>
#    include <queue>
#    include <thread>
#endif  // (ANGLE_DELEGATE_WORKERS == ANGLE_ENABLED) || (ANGLE_STD_ASYNC_WORKERS == ANGLE_ENABLED)

namespace angle
{

WaitableEvent::WaitableEvent()  = default;
WaitableEvent::~WaitableEvent() = default;

void WaitableEventDone::wait() {}

bool WaitableEventDone::isReady()
{
    return true;
}

WorkerThreadPool::WorkerThreadPool()  = default;
WorkerThreadPool::~WorkerThreadPool() = default;

class SingleThreadedWaitableEvent final : public WaitableEvent
{
  public:
    SingleThreadedWaitableEvent()           = default;
    ~SingleThreadedWaitableEvent() override = default;

    void wait() override;
    bool isReady() override;
};

void SingleThreadedWaitableEvent::wait() {}

bool SingleThreadedWaitableEvent::isReady()
{
    return true;
}

class SingleThreadedWorkerPool final : public WorkerThreadPool
{
  public:
    std::shared_ptr<WaitableEvent> postWorkerTask(std::shared_ptr<Closure> task) override;
    void setMaxThreads(size_t maxThreads) override;
    bool isAsync() override;
};

// SingleThreadedWorkerPool implementation.
std::shared_ptr<WaitableEvent> SingleThreadedWorkerPool::postWorkerTask(
    std::shared_ptr<Closure> task)
{
    (*task)();
    return std::make_shared<SingleThreadedWaitableEvent>();
}

void SingleThreadedWorkerPool::setMaxThreads(size_t maxThreads) {}

bool SingleThreadedWorkerPool::isAsync()
{
    return false;
}

#if (ANGLE_STD_ASYNC_WORKERS == ANGLE_ENABLED)
class AsyncWaitableEvent final : public WaitableEvent
{
  public:
    AsyncWaitableEvent() : mIsPending(true) {}
    ~AsyncWaitableEvent() override = default;

    void wait() override;
    bool isReady() override;

  private:
    friend class AsyncWorkerPool;
    void setFuture(std::future<void> &&future);

    // To block wait() when the task is still in queue to be run.
    // Also to protect the concurrent accesses from both main thread and
    // background threads to the member fields.
    std::mutex mMutex;

    bool mIsPending;
    std::condition_variable mCondition;
    std::future<void> mFuture;
};

void AsyncWaitableEvent::setFuture(std::future<void> &&future)
{
    mFuture = std::move(future);
}

void AsyncWaitableEvent::wait()
{
    ANGLE_TRACE_EVENT0("gpu.angle", "AsyncWaitableEvent::wait");
    {
        std::unique_lock<std::mutex> lock(mMutex);
        mCondition.wait(lock, [this] { return !mIsPending; });
    }

    ASSERT(mFuture.valid());
    mFuture.wait();
}

bool AsyncWaitableEvent::isReady()
{
    std::lock_guard<std::mutex> lock(mMutex);
    if (mIsPending)
    {
        return false;
    }
    ASSERT(mFuture.valid());
    return mFuture.wait_for(std::chrono::seconds(0)) == std::future_status::ready;
}

class AsyncWorkerPool final : public WorkerThreadPool
{
  public:
    AsyncWorkerPool(size_t maxThreads) : mMaxThreads(maxThreads), mRunningThreads(0) {}
    ~AsyncWorkerPool() override = default;

    std::shared_ptr<WaitableEvent> postWorkerTask(std::shared_ptr<Closure> task) override;
    void setMaxThreads(size_t maxThreads) override;
    bool isAsync() override;

  private:
    void checkToRunPendingTasks();

    // To protect the concurrent accesses from both main thread and background
    // threads to the member fields.
    std::mutex mMutex;

    size_t mMaxThreads;
    size_t mRunningThreads;
    std::queue<std::pair<std::shared_ptr<AsyncWaitableEvent>, std::shared_ptr<Closure>>> mTaskQueue;
};

// AsyncWorkerPool implementation.
std::shared_ptr<WaitableEvent> AsyncWorkerPool::postWorkerTask(std::shared_ptr<Closure> task)
{
    ASSERT(mMaxThreads > 0);

    auto waitable = std::make_shared<AsyncWaitableEvent>();
    {
        std::lock_guard<std::mutex> lock(mMutex);
        mTaskQueue.push(std::make_pair(waitable, task));
    }
    checkToRunPendingTasks();
    return std::move(waitable);
}

void AsyncWorkerPool::setMaxThreads(size_t maxThreads)
{
    {
        std::lock_guard<std::mutex> lock(mMutex);
        mMaxThreads = (maxThreads == 0xFFFFFFFF ? std::thread::hardware_concurrency() : maxThreads);
    }
    checkToRunPendingTasks();
}

bool AsyncWorkerPool::isAsync()
{
    return true;
}

void AsyncWorkerPool::checkToRunPendingTasks()
{
    std::lock_guard<std::mutex> lock(mMutex);
    while (mRunningThreads < mMaxThreads && !mTaskQueue.empty())
    {
        auto task = mTaskQueue.front();
        mTaskQueue.pop();
        auto waitable = task.first;
        auto closure  = task.second;

        auto future = std::async(std::launch::async, [closure, this] {
            {
                ANGLE_TRACE_EVENT0("gpu.angle", "AsyncWorkerPool::RunTask");
                (*closure)();
            }
            {
                std::lock_guard<std::mutex> lock(mMutex);
                ASSERT(mRunningThreads != 0);
                --mRunningThreads;
            }
            checkToRunPendingTasks();
        });

        ++mRunningThreads;

        {
            std::lock_guard<std::mutex> waitableLock(waitable->mMutex);
            waitable->mIsPending = false;
            waitable->setFuture(std::move(future));
        }
        waitable->mCondition.notify_all();
    }
}
#endif  // (ANGLE_STD_ASYNC_WORKERS == ANGLE_ENABLED)

#if (ANGLE_DELEGATE_WORKERS == ANGLE_ENABLED)
class DelegateWaitableEvent final : public WaitableEvent
{
  public:
    DelegateWaitableEvent()           = default;
    ~DelegateWaitableEvent() override = default;

    void wait() override;
    bool isReady() override;

    void markAsReady();

  private:
    // To protect the concurrent accesses from both main thread and background
    // threads to the member fields.
    std::mutex mMutex;

    bool mIsReady = false;
    std::condition_variable mCondition;
};

void DelegateWaitableEvent::markAsReady()
{
    std::lock_guard<std::mutex> lock(mMutex);
    mIsReady = true;
    mCondition.notify_all();
}

void DelegateWaitableEvent::wait()
{
    std::unique_lock<std::mutex> lock(mMutex);
    mCondition.wait(lock, [this] { return mIsReady; });
}

bool DelegateWaitableEvent::isReady()
{
    std::lock_guard<std::mutex> lock(mMutex);
    return mIsReady;
}

class DelegateWorkerPool final : public WorkerThreadPool
{
  public:
    DelegateWorkerPool()           = default;
    ~DelegateWorkerPool() override = default;

    std::shared_ptr<WaitableEvent> postWorkerTask(std::shared_ptr<Closure> task) override;

    void setMaxThreads(size_t maxThreads) override;
    bool isAsync() override;
};

// A function wrapper to execute the closure and to notify the waitable
// event after the execution.
class DelegateWorkerTask
{
  public:
    DelegateWorkerTask(std::shared_ptr<Closure> task,
                       std::shared_ptr<DelegateWaitableEvent> waitable)
        : mTask(task), mWaitable(waitable)
    {}
    DelegateWorkerTask()                     = delete;
    DelegateWorkerTask(DelegateWorkerTask &) = delete;

    static void RunTask(void *userData)
    {
        DelegateWorkerTask *workerTask = static_cast<DelegateWorkerTask *>(userData);
        (*workerTask->mTask)();
        workerTask->mWaitable->markAsReady();

        // Delete the task after its execution.
        delete workerTask;
    }

  private:
    ~DelegateWorkerTask() = default;

    std::shared_ptr<Closure> mTask;
    std::shared_ptr<DelegateWaitableEvent> mWaitable;
};

std::shared_ptr<WaitableEvent> DelegateWorkerPool::postWorkerTask(std::shared_ptr<Closure> task)
{
    auto waitable = std::make_shared<DelegateWaitableEvent>();

    // The task will be deleted by DelegateWorkerTask::RunTask(...) after its execution.
    DelegateWorkerTask *workerTask = new DelegateWorkerTask(task, waitable);
    auto *platform                 = ANGLEPlatformCurrent();
    platform->postWorkerTask(platform, DelegateWorkerTask::RunTask, workerTask);

    return std::move(waitable);
}

void DelegateWorkerPool::setMaxThreads(size_t maxThreads) {}

bool DelegateWorkerPool::isAsync()
{
    return true;
}
#endif

// static
std::shared_ptr<WorkerThreadPool> WorkerThreadPool::Create(bool multithreaded)
{
    std::shared_ptr<WorkerThreadPool> pool(nullptr);

#if (ANGLE_DELEGATE_WORKERS == ANGLE_ENABLED)
    const bool hasPostWorkerTaskImpl = ANGLEPlatformCurrent()->postWorkerTask;
    if (hasPostWorkerTaskImpl && multithreaded)
    {
        pool = std::shared_ptr<WorkerThreadPool>(new DelegateWorkerPool());
    }
#endif
#if (ANGLE_STD_ASYNC_WORKERS == ANGLE_ENABLED)
    if (!pool && multithreaded)
    {
        pool = std::shared_ptr<WorkerThreadPool>(
            new AsyncWorkerPool(std::thread::hardware_concurrency()));
    }
#endif
    if (!pool)
    {
        return std::shared_ptr<WorkerThreadPool>(new SingleThreadedWorkerPool());
    }
    return pool;
}

// static
std::shared_ptr<WaitableEvent> WorkerThreadPool::PostWorkerTask(
    std::shared_ptr<WorkerThreadPool> pool,
    std::shared_ptr<Closure> task)
{
    std::shared_ptr<WaitableEvent> event = pool->postWorkerTask(task);
    if (event.get())
    {
        event->setWorkerThreadPool(pool);
    }
    return event;
}

}  // namespace angle