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  • Posix 信号量

    作用

    信号量的值为0或正整数,就像红灯与绿灯,用于指示当前是否可以接受任务.
    信号量对进程和线程都适用.
    gcc编译时需加-lpthread

    基本函数

    信号量的相关函数与标准文件函数非常相似,可以理解文件的读写,只是读写对象不同而已

    #include <semaphore.h>
    sem_t *sem_open(const char *name,int oflag,...
            /* mode_t mode,unsigned int value */);
    int sem_close(sem_t *sem);
    int sem_unlink(const char *name);
    int sem_wait(sem_t *sem);
    int sem_trywait(sem_t *sem);
    int sem_post(sem_t *sem);
    int sem_getvalue(sem_t *sem,int *valp);
    

    例子

    #include "./unpipc.h"
    #include <semaphore.h>
    #include <pthread.h>
     
    #define NBUFF 10
    #define SEM_MUTEX "/mutex"
    #define SEM_NEMPTY "/empty"
    #define SEM_NSTORED "/nstored"
     
    int nitems;
    struct {
        int buff[NBUFF];
        sem_t *mutex,*nempty,*nstored;
    } shared;
     
    void *produce(void *), *consume(void *);
     
    int main(int argc,char *argv[]){
        pthread_t tid_produce,tid_consume;
     
        if(argc != 2)
            err_quit("usage: sem <#items>");
        nitems=atoi(argv[1]);
     
        shared.mutex=sem_open(SEM_MUTEX,O_CREAT|O_EXCL,0644,1);
        shared.nempty=sem_open(SEM_NEMPTY,O_CREAT|O_EXCL,0644,NBUFF);
        shared.nstored=sem_open(SEM_NSTORED,O_CREAT|O_EXCL,0644,0);
     
        pthread_setconcurrency(2);
        pthread_create(&tid_produce,NULL,produce,NULL);
        pthread_create(&tid_consume,NULL,consume,NULL);
     
        pthread_join(tid_produce,NULL);
        pthread_join(tid_consume,NULL);
     
        sem_unlink(SEM_MUTEX);
        sem_unlink(SEM_NEMPTY);
        sem_unlink(SEM_NSTORED);
        exit(0);
    }
     
    void *
    produce(void *arg){
        int i;
     
        for(i=0;i<nitems;i++){
            sem_wait(shared.nempty);
            sem_wait(shared.mutex);
            shared.buff[i%NBUFF]=i;
            sem_post(shared.mutex);
            sem_post(shared.nstored);
        }
        return(NULL);
    }
    void *
    consume(void *arg){
        int i;
     
        for(i=0;i<nitems;i++){
            sem_wait(shared.nstored);
            sem_wait(shared.mutex);
            if(shared.buff[i%NBUFF] != i)
                printf("buff[%d]=%d
    ",i,shared.buff[i%NBUFF]);
            sem_post(shared.mutex);
            sem_post(shared.nempty);
        }
        return(NULL);
    }
    
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  • 原文地址:https://www.cnblogs.com/cfans1993/p/5813725.html
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