Linux信号量编程实例

Linux信号量编程实例

    本例示范Linux信号量的基本用法。该范例使用了两个线程分别对一个公用队列进行入队和出队操作，并用信号量进行控制，当队列空时出队操作可以被阻塞，当队列满时入队操作可以被阻塞。

主要用到的信号量函数有：

sem_init：初始化信号量sem_t，初始化的时候可以指定信号量的初始值，以及是否可以在多进程间共享。

sem_wait：一直阻塞等待直到信号量>0。

sem_timedwait：阻塞等待若干时间直到信号量>0。

sem_post：使信号量加1。

sem_destroy：释放信号量。和sem_init对应。

关于各函数的具体参数请用man查看。如man sem_init可查看该函数的帮助。

下面看具体的代码：

//--------------------------msgdequeue.h开始-------------------------------------

//实现可控队列

#ifndef MSGDEQUEUE_H

#define MSGDEQUEUE_H

#include "tmutex.h"

#include <iostream>

#include <errno.h>

#include <time.h>

#include <semaphore.h>

#include <deque>

using namespace std;

template<typename T,typename MUTEX_TYPE = ThreadMutex>

class CMessageDequeue

{

public:

        CMessageDequeue(size_t MaxSize) : m_MaxSize( MaxSize )

        {

                sem_init( &m_enques,0, m_MaxSize ); //入队信号量初始化为MaxSize，最多可容纳MaxSize各元素

                sem_init( &m_deques,0,0 ); //队列刚开始为空，出队信号量初始为0

        }

        ~CMessageDequeue()

        {

                sem_destroy(&m_enques);

                sem_destroy(&m_deques);

        }

        int sem_wait_i( sem_t *psem, int mswait )

        {//等待信号量变成>0，mswait为等待时间，若mswait<0则无穷等待，否则等待若干mswait毫秒。

                if( mswait < 0 )

                {

                        int rv = 0;                          

                        while( ((rv = sem_wait(psem) ) != 0 ) && (errno == EINTR

) );    //等待信号量，errno==EINTR屏蔽其他信号事件引起的等待中断

                        return rv;   

                }                                           

                else                                        

                {                                           

                        timespec ts;                        

                        clock_gettime(CLOCK_REALTIME, &ts );    //获取当前时间

                        ts.tv_sec += (mswait / 1000 );        //加上等待时间的秒数

                        ts.tv_nsec += ( mswait % 1000 ) * 1000; //加上等待时间纳秒数

                        int rv = 0;                         

                        while( ((rv=sem_timedwait( psem, &ts ))!=0) && (errno ==

EINTR) );   //等待信号量，errno==EINTR屏蔽其他信号事件引起的等待中断

                        return rv;  

                }                                           

        }                                                   

        bool push_back( const T &item, int mswait = -1 )    

        { //等待mswait毫秒直到将item插入队列，mswait为-1则一直等待                                                  

                if( -1 == sem_wait_i( &m_enques, mswait ))  

                {                                           

                        return false;                       

                }

                  //AUTO_GUARD：定界加锁，见Linux多线程及临界区编程例解的tmutex.h文件定义。                            

                AUTO_GUARD( g, MUTEX_TYPE, m_lock );

                try                                         

                {                                            

                        m_data.push_back( item );           

                        cout << "push " << item << endl;    

                        sem_post( &m_deques );              

                        return true;                         

                }                                           

                catch(...)                                  

                {                                           

                        return false;                        

                }                                           

        }       

      bool pop_front( T &item, bool bpop = true, int mswait = -1 )     

        { //等待mswait毫秒直到从队列取出元素，mswait为-1则一直等待                                                    

                if( -1 == sem_wait_i( &m_deques, mswait ) ) 

                {                                           

                        return false;                       

                }          

                 //AUTO_GUARD：定界加锁，见Linux多线程及临界区编程例解的tmutex.h文件定义。                  

                AUTO_GUARD( g, MUTEX_TYPE, m_lock );        

                try                                         

                {                                           

                        item = m_data.front();              

                        if( bpop )                          

                        {                                   

                                m_data.pop_front();         

                                cout << "pop " << item << endl;

                        }                                   

                        sem_post( &m_enques );              

                        return true;                        

                }                                           

                catch(...)                                  

                {                                           

                        return false;                       

                }                                           

        }                                                   

        inline size_t size()                                

        {                                                    

                return m_data.size();                       

        }    

private:                                                    

        MUTEX_TYPE m_lock;                                  

        deque<T> m_data;                                    

        size_t m_MaxSize;                                   

        sem_t m_enques;                                     

        sem_t m_deques;                                     

};                                                           

#endif                        

//--------------------------msgdequeue.h结束-------------------------------------

//--------------------------test.cpp开始-------------------------------------

//主程序文件

#include "msgdequeue.h"

#include <pthread.h>

#include <iostream>

using namespace std;

CMessageDequeue<int> qq(5);

void *get_thread(void *parg);

void *put_thread(void *parg);

void *get_thread(void *parg)

{

        while(true)

        {

                int a = -1;

                if( !qq.pop_front( a,true, 1000 ) )

                {

                        cout << "pop failed. size=" << qq.size() << endl;

                }

        }

        return NULL;

}

void *put_thread(void *parg)

{

        for(int i=1; i<=30; i++)

        {

                qq.push_back( i, -1 );

        }

        return NULL;                                        

}                                                           

int main()                                                  

{                                                         

        pthread_t pget,pput;                                

        pthread_create( &pget,NULL,get_thread,NULL);        

        pthread_create( &pput, NULL, put_thread,NULL);      

        pthread_join( pget,NULL );                          

        pthread_join( pput,NULL );                          

        return 0;                                           

}     

//--------------------------test.cpp结束-------------------------------------

    编译程序：g++ msgdequeue.h test.cpp -lpthread -lrt -o test

    -lpthread链接pthread库。-ltr链接clock_gettime函数相关库。

    编译后生成可执行文件test。输入./test执行程序。

    线程get_thread每隔1000毫秒从队列取元素，线程put_thread将30个元素依次入队。两个线程模拟两条入队和出队的流水线。因我们在CMessageDequeue<int> qq(5)处定义了队列最多可容纳5个元素，入队线程每入队到队列元素满5个后需阻塞等待出队线程将队列元素出队才能继续。测试时可调整队列可容纳最大元素个数来观察运行效果。