/*
 * Copyright (C) 2015 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. ``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
 * 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 "ParallelHelperPool.h"

#include "DataLog.h"
#include "StringPrintStream.h"

namespace WTF {

ParallelHelperClient::ParallelHelperClient(RefPtr<ParallelHelperPool> pool)
    : m_pool(pool)
{
    LockHolder locker(m_pool->m_lock);
    RELEASE_ASSERT(!m_pool->m_isDying);
    m_pool->m_clients.append(this);
}

ParallelHelperClient::~ParallelHelperClient()
{
    LockHolder locker(m_pool->m_lock);
    finish(locker);

    for (size_t i = 0; i < m_pool->m_clients.size(); ++i) {
        if (m_pool->m_clients[i] == this) {
            m_pool->m_clients[i] = m_pool->m_clients.last();
            m_pool->m_clients.removeLast();
            break;
        }
    }
}

void ParallelHelperClient::setTask(RefPtr<SharedTask<void ()>> task)
{
    LockHolder locker(m_pool->m_lock);
    RELEASE_ASSERT(!m_task);
    m_task = task;
    m_pool->didMakeWorkAvailable(locker);
}

void ParallelHelperClient::finish()
{
    LockHolder locker(m_pool->m_lock);
    finish(locker);
}

void ParallelHelperClient::doSomeHelping()
{
    RefPtr<SharedTask<void ()>> task;
    {
        LockHolder locker(m_pool->m_lock);
        task = claimTask(locker);
        if (!task)
            return;
    }

    runTask(task);
}

void ParallelHelperClient::runTaskInParallel(RefPtr<SharedTask<void ()>> task)
{
    setTask(task);
    doSomeHelping();
    finish();
}

void ParallelHelperClient::finish(const LockHolder&)
{
    m_task = nullptr;
    while (m_numActive)
        m_pool->m_workCompleteCondition.wait(m_pool->m_lock);
}

RefPtr<SharedTask<void ()>> ParallelHelperClient::claimTask(const LockHolder&)
{
    if (!m_task)
        return nullptr;
    
    m_numActive++;
    return m_task;
}

void ParallelHelperClient::runTask(RefPtr<SharedTask<void ()>> task)
{
    RELEASE_ASSERT(m_numActive);
    RELEASE_ASSERT(task);

    task->run();

    {
        LockHolder locker(m_pool->m_lock);
        RELEASE_ASSERT(m_numActive);
        // No new task could have been installed, since we were still active.
        RELEASE_ASSERT(!m_task || m_task == task);
        m_task = nullptr;
        m_numActive--;
        if (!m_numActive)
            m_pool->m_workCompleteCondition.notifyAll();
    }
}

ParallelHelperPool::ParallelHelperPool()
{
}

ParallelHelperPool::~ParallelHelperPool()
{
    RELEASE_ASSERT(m_clients.isEmpty());
    
    {
        LockHolder locker(m_lock);
        m_isDying = true;
        m_workAvailableCondition.notifyAll();
    }

    for (ThreadIdentifier threadIdentifier : m_threads)
        waitForThreadCompletion(threadIdentifier);
}

void ParallelHelperPool::ensureThreads(unsigned numThreads)
{
    LockHolder locker(m_lock);
    if (numThreads < m_numThreads)
        return;
    m_numThreads = numThreads;
    if (getClientWithTask(locker))
        didMakeWorkAvailable(locker);
}

void ParallelHelperPool::doSomeHelping()
{
    ParallelHelperClient* client;
    RefPtr<SharedTask<void ()>> task;
    {
        LockHolder locker(m_lock);
        client = getClientWithTask(locker);
        if (!client)
            return;
        task = client->claimTask(locker);
    }

    client->runTask(task);
}

void ParallelHelperPool::didMakeWorkAvailable(const LockHolder&)
{
    while (m_numThreads > m_threads.size()) {
        ThreadIdentifier threadIdentifier = createThread(
            "WTF Parallel Helper Thread",
            [this] () {
                helperThreadBody();
            });
        m_threads.append(threadIdentifier);
    }
    m_workAvailableCondition.notifyAll();
}

void ParallelHelperPool::helperThreadBody()
{
    for (;;) {
        ParallelHelperClient* client;
        RefPtr<SharedTask<void ()>> task;

        {
            LockHolder locker(m_lock);
            client = waitForClientWithTask(locker);
            if (!client) {
                RELEASE_ASSERT(m_isDying);
                return;
            }

            task = client->claimTask(locker);
        }

        client->runTask(task);
    }
}

bool ParallelHelperPool::hasClientWithTask(const LockHolder& locker)
{
    return !!getClientWithTask(locker);
}

ParallelHelperClient* ParallelHelperPool::getClientWithTask(const LockHolder&)
{
    // We load-balance by being random.
    unsigned startIndex = m_random.getUint32(m_clients.size());
    for (unsigned index = startIndex; index < m_clients.size(); ++index) {
        ParallelHelperClient* client = m_clients[index];
        if (client->m_task)
            return client;
    }
    for (unsigned index = 0; index < startIndex; ++index) {
        ParallelHelperClient* client = m_clients[index];
        if (client->m_task)
            return client;
    }

    return nullptr;
}

ParallelHelperClient* ParallelHelperPool::waitForClientWithTask(const LockHolder& locker)
{
    for (;;) {
        // It might be quittin' time.
        if (m_isDying)
            return nullptr;

        if (ParallelHelperClient* result = getClientWithTask(locker))
            return result;

        // Wait until work becomes available.
        m_workAvailableCondition.wait(m_lock);
    }
}

} // namespace WTF