Boost条件变量condition_variable_any

　　Boost条件变量可以用来实现线程同步，它必须与互斥量配合使用。使用条件变量实现生产者消费者的简单例子如下，需要注意的是cond_put.wait(lock)是在等待条件满足。如果条件不满足，则释放锁，将线程置为waiting状态，继续等待；如果条件满足，则重新获取锁，然后结束wait，继续向下执行。

#include "stdafx.h"
#include <stack>
#include <boost/bind/bind.hpp>
#include <boost/thread.hpp>
#include <boost/thread/lock_factories.hpp>
using namespace std;
class Buffer
{
private:
    boost::mutex mu;

    boost::condition_variable_any cond_put;
    boost::condition_variable_any cond_get;
    int un_read, capacity;

    std::stack<int> m_stk;
    bool isFull()
    {
        return un_read == capacity;
    }
    bool isEmpty()
    {
        return un_read == 0;
    }
public:
    Buffer(size_t n):un_read(0), capacity(n) {}

    void put(int x)
    {
        {
            auto lock = make_unique_lock(mu);
            for (; isFull(); )
            {
                cout << "Full waiting"<<endl;
                cond_put.wait(lock);
            }
            m_stk.push(x);
            ++un_read;
        }
        cond_get.notify_one();
    }

    void get(int *x)
    {
        {
            auto lock = make_unique_lock(mu);
            for (; isEmpty(); )
            {
                cout<<"Empty waiting..."<<endl;
                cond_get.wait(lock);
            }
            --un_read;
            *x = m_stk.top();
            m_stk.pop();
        }
        cond_put.notify_one();
    }

};

Buffer buf(5);
void Producer(int n)
{
    for (int i=0; i<n; i++)
    {
        cout<< "Putting "<<i<<endl;
        buf.put(i);
    }
}

void Consumer(int n)
{
    int x;
    for (int i=0; i<n; i++)
    {
        buf.get(&x);
        cout<<"Getting "<<x<<endl;
    }
}

int main()
{
    boost::thread_group tg;
    tg.create_thread(bind(Producer, 20));

    tg.create_thread(bind(Consumer, 10));
    tg.create_thread(bind(Consumer, 10));

    tg.join_all();

    return 0;
}