muduo之BlockingQueue

         BlockingQueue是muduo是无界队列，利用队列(deque)实现，向队列中加入和取出元素用互斥量和条件变量结合的方式来操作，就是一个线程同步的问题。

BlockingQueue.h

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#ifndef MUDUO_BASE_BLOCKINGQUEUE_H
#define MUDUO_BASE_BLOCKINGQUEUE_H

#include "muduo/base/Condition.h"
#include "muduo/base/Mutex.h"

#include <deque>
#include <assert.h>

namespace muduo
{
//互斥锁配合条件变量是为了防止线程不停的主动获得锁、检查条件、释放锁、再获得锁、再检查、再释放，一直到满足运行的条件的时候才行
template<typename T>
class BlockingQueue : noncopyable  //无界阻塞队列
{
 public:
  BlockingQueue()
    : mutex_(),
      notEmpty_(mutex_),   //条件变量
      queue_()
  {
  }

  void put(const T& x)
  {
    MutexLockGuard lock(mutex_);
    queue_.push_back(x);
    notEmpty_.notify(); // wait morphing saves us
    // http://www.domaigne.com/blog/computing/condvars-signal-with-mutex-locked-or-not/
  }

  void put(T&& x)
  {
    MutexLockGuard lock(mutex_);
    queue_.push_back(std::move(x));
    notEmpty_.notify();//向所有线程提示条件已发生
  }

  T take()
  {
    MutexLockGuard lock(mutex_);
    // always use a while-loop, due to spurious wakeup
    while (queue_.empty())
    {
      notEmpty_.wait();  //等待条件发生
    }
    assert(!queue_.empty());
    T front(std::move(queue_.front()));//掏空queue_.front()，queue_.front()就变为空了
    queue_.pop_front();
    return std::move(front);
  }

  size_t size() const
  {
    MutexLockGuard lock(mutex_);
    return queue_.size();
  }

 private:
  mutable MutexLock mutex_;
  Condition         notEmpty_ GUARDED_BY(mutex_);
  std::deque<T>     queue_ GUARDED_BY(mutex_);
};

}  // namespace muduo

#endif  // MUDUO_BASE_BLOCKINGQUEUE_H