trinitycore 魔兽服务器源码分析(三) 多线程相关

先看LockedQueue.h

template <class T, typename StorageType = std::deque<T> >
class LockedQueue{......}

一个带锁的多线程可安全访问的类，容器默认使用std::deque

常规代码 push进T类型的元素 pop出T类型的元素

使用锁定 保证线程安全 

相比C++11之前的繁琐做法 现在加锁可以使用 std::lock_guard

当使用std::lock_guard<std::mutex> lock(_lock)后 代码进入加锁模式

脱出lock的变量生存周期时候 自动解锁

代码如下

/*
 * Copyright (C) 2008-2017 TrinityCore <http://www.trinitycore.org/>
 * Copyright (C) 2005-2008 MaNGOS <http://getmangos.com/>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef LOCKEDQUEUE_H
#define LOCKEDQUEUE_H

#include <deque>
#include <mutex>

template <class T, typename StorageType = std::deque<T> >
class LockedQueue
{
    //! Lock access to the queue.
    std::mutex _lock;

    //! Storage backing the queue.
    StorageType _queue;

    //! Cancellation flag.
    volatile bool _canceled;

public:

    //! Create a LockedQueue.
    LockedQueue()
        : _canceled(false)
    {
    }

    //! Destroy a LockedQueue.
    virtual ~LockedQueue()
    {
    }

    //! Adds an item to the queue.
    void add(const T& item)
    {
        lock();

        _queue.push_back(item);

        unlock();
    }

    //! Adds items back to front of the queue
    template<class Iterator>
    void readd(Iterator begin, Iterator end)
    {
        std::lock_guard<std::mutex> lock(_lock);
        _queue.insert(_queue.begin(), begin, end);
    }

    //! Gets the next result in the queue, if any.
    bool next(T& result)
    {
        std::lock_guard<std::mutex> lock(_lock);

        if (_queue.empty())
            return false;

        result = _queue.front();
        _queue.pop_front();

        return true;
    }

    template<class Checker>
    bool next(T& result, Checker& check)
    {
        std::lock_guard<std::mutex> lock(_lock);

        if (_queue.empty())
            return false;

        result = _queue.front();
        if (!check.Process(result))
            return false;

        _queue.pop_front();
        return true;
    }

    //! Peeks at the top of the queue. Check if the queue is empty before calling! Remember to unlock after use if autoUnlock == false.
    T& peek(bool autoUnlock = false)
    {
        lock();

        T& result = _queue.front();

        if (autoUnlock)
            unlock();

        return result;
    }

    //! Cancels the queue.
    void cancel()
    {
        std::lock_guard<std::mutex> lock(_lock);

        _canceled = true;
    }

    //! Checks if the queue is cancelled.
    bool cancelled()
    {
        std::lock_guard<std::mutex> lock(_lock);
        return _canceled;
    }

    //! Locks the queue for access.
    void lock()
    {
        this->_lock.lock();
    }

    //! Unlocks the queue.
    void unlock()
    {
        this->_lock.unlock();
    }

    ///! Calls pop_front of the queue
    void pop_front()
    {
        std::lock_guard<std::mutex> lock(_lock);
        _queue.pop_front();
    }

    ///! Checks if we're empty or not with locks held
    bool empty()
    {
        std::lock_guard<std::mutex> lock(_lock);
        return _queue.empty();
    }
};
#endif

//=========================================================

MPSCQueue.h

这是一个操作原子类型的元素指针的链表队列

template<typename T>
class MPSCQueue
{
std::atomic<Node*> _head;
std::atomic<Node*> _tail;
}

Node就是一个链表的类型  当我们使用exchange交换Node的指针时 是多线程安全的

而std::memory_order_acq_rel 类似的原子操作的内存模式参数

可参考

http://www.1024cores.net/home/lock-free-algorithms/queues/non-intrusive-mpsc-node-based-queue

https://www.zhihu.com/question/24301047

源码

/*
 * Copyright (C) 2008-2017 TrinityCore <http://www.trinitycore.org/>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef MPSCQueue_h__
#define MPSCQueue_h__

#include <atomic>
#include <utility>

// C++ implementation of Dmitry Vyukov's lock free MPSC queue
// http://www.1024cores.net/home/lock-free-algorithms/queues/non-intrusive-mpsc-node-based-queue
template<typename T>
class MPSCQueue
{
public:
    MPSCQueue() : _head(new Node()), _tail(_head.load(std::memory_order_relaxed))
    {
        Node* front = _head.load(std::memory_order_relaxed);
        front->Next.store(nullptr, std::memory_order_relaxed);
    }

    ~MPSCQueue()
    {
        T* output;
        while (this->Dequeue(output))
            ;

        Node* front = _head.load(std::memory_order_relaxed);
        delete front;
    }

    void Enqueue(T* input)
    {
        Node* node = new Node(input);
        Node* prevHead = _head.exchange(node, std::memory_order_acq_rel);
        prevHead->Next.store(node, std::memory_order_release);
    }

    bool Dequeue(T*& result)
    {
        Node* tail = _tail.load(std::memory_order_relaxed);
        Node* next = tail->Next.load(std::memory_order_acquire);
        if (!next)
            return false;

        result = next->Data;
        _tail.store(next, std::memory_order_release);
        delete tail;
        return true;
    }

private:
    struct Node
    {
        Node() = default;
        explicit Node(T* data) : Data(data) { Next.store(nullptr, std::memory_order_relaxed); }

        T* Data;
        std::atomic<Node*> Next;
    };

    std::atomic<Node*> _head;
    std::atomic<Node*> _tail;

    MPSCQueue(MPSCQueue const&) = delete;
    MPSCQueue& operator=(MPSCQueue const&) = delete;
};

#endif // MPSCQueue_h__

//=========================================================================

使用多线程安全的队列 设计出一个生产消费者队列

template <typename T>
class ProducerConsumerQueue
{

private:
std::mutex _queueLock;　　　　　　　　//进行操作时候的锁
std::queue<T> _queue;　　　　　　　　// 存储元素的队列
std::condition_variable _condition;　　　//条件变量
std::atomic<bool> _shutdown;　　　　　//原子类型的标记 标记此队列是否关闭

}

//构造函数

ProducerConsumerQueue<T>() : _shutdown(false) { }

// 加锁情况下  生产者push元素进队列 并通过条件变量提示消费者进行处理

void Push(const T& value)
{
std::lock_guard<std::mutex> lock(_queueLock);
_queue.push(std::move(value));

_condition.notify_one();
}

//加锁模式下 判断队列是否为空

bool Empty()
{
std::lock_guard<std::mutex> lock(_queueLock);

return _queue.empty();
}

//加锁模式下 队列不空且没有shuntdown关闭标记 进行元素弹出操作

bool Pop(T& value)
{
std::lock_guard<std::mutex> lock(_queueLock);

if (_queue.empty() || _shutdown)
return false;

value = _queue.front();

_queue.pop();

return true;
}

//消费者调用 加锁模式在未有元素的处理下进行等待元素

void WaitAndPop(T& value)
{
std::unique_lock<std::mutex> lock(_queueLock);

// we could be using .wait(lock, predicate) overload here but it is broken
// https://connect.microsoft.com/VisualStudio/feedback/details/1098841
while (_queue.empty() && !_shutdown)
_condition.wait(lock);

if (_queue.empty() || _shutdown)
return;

value = _queue.front();

_queue.pop();
}

void Cancel()
{
std::unique_lock<std::mutex> lock(_queueLock);

while (!_queue.empty())
{
T& value = _queue.front();

DeleteQueuedObject(value);

_queue.pop();
}

_shutdown = true;

_condition.notify_all();
}

//c++ 模板 template的小技巧 SFINAE (substitution-failure-is-not-an-error) 原则
//根据传入的模板参数是否是指针 而适配到不同的处理函数中 如果是指针类型则在删除时 delete指针
//否则适配到另个函数 删除时候什么都不做

template<typename E = T>
typename std::enable_if<std::is_pointer<E>::value>::type DeleteQueuedObject(E& obj) { delete obj; }

template<typename E = T>
typename std::enable_if<!std::is_pointer<E>::value>::type DeleteQueuedObject(E const& /*packet*/) { }

/*
 * Copyright (C) 2008-2017 TrinityCore <http://www.trinitycore.org/>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef _PCQ_H
#define _PCQ_H

#include <condition_variable>
#include <mutex>
#include <queue>
#include <atomic>
#include <type_traits>

template <typename T>
class ProducerConsumerQueue
{
private:
    std::mutex _queueLock;
    std::queue<T> _queue;
    std::condition_variable _condition;
    std::atomic<bool> _shutdown;

public:

    ProducerConsumerQueue<T>() : _shutdown(false) { }

    void Push(const T& value)
    {
        std::lock_guard<std::mutex> lock(_queueLock);
        _queue.push(std::move(value));

        _condition.notify_one();
    }

    bool Empty()
    {
        std::lock_guard<std::mutex> lock(_queueLock);

        return _queue.empty();
    }

    bool Pop(T& value)
    {
        std::lock_guard<std::mutex> lock(_queueLock);

        if (_queue.empty() || _shutdown)
            return false;

        value = _queue.front();

        _queue.pop();

        return true;
    }

    void WaitAndPop(T& value)
    {
        std::unique_lock<std::mutex> lock(_queueLock);

        // we could be using .wait(lock, predicate) overload here but it is broken
        // https://connect.microsoft.com/VisualStudio/feedback/details/1098841
        while (_queue.empty() && !_shutdown)
            _condition.wait(lock);

        if (_queue.empty() || _shutdown)
            return;

        value = _queue.front();

        _queue.pop();
    }

    void Cancel()
    {
        std::unique_lock<std::mutex> lock(_queueLock);

        while (!_queue.empty())
        {
            T& value = _queue.front();

            DeleteQueuedObject(value);

            _queue.pop();
        }

        _shutdown = true;

        _condition.notify_all();
    }

private:
    template<typename E = T>
    typename std::enable_if<std::is_pointer<E>::value>::type DeleteQueuedObject(E& obj) { delete obj; }

    template<typename E = T>
    typename std::enable_if<!std::is_pointer<E>::value>::type DeleteQueuedObject(E const& /*packet*/) { }
};

#endif