进程间通信：用信号量实现对共享内存读写顺序的控制

这本是一道题：一本是一个全局变量来做的控制共享内存通信方式，一个已经实现的信号量通信，最终的结果是让这两个掺和在一起。用信号量来控制共享内存通信的读写顺序。

            原本信号量通信方式的函数在这是，原本的共享内存程序在这里。

            做的最新的结果是可以通信了，但是在客户端有一点点异常，就是在服务器端还没有释放信号量，但是客户端不可以获取的，这使我很疑惑。

服务器端：

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include "shm_com.h"

#include <sys/sem.h>

#include <signal.h>
/********************************************************/
int pid,semid;
/********************************************************/

void my_func(int sign_no)
{
    if(sign_no==SIGINT)
    {
        printf("\nYes Sir,I have get SIGINT\n");
        if(semctl(semid, 0, IPC_RMID, 0)<0)
        {
            printf("semctl remove semaphore set failed\n");
            exit(EXIT_FAILURE);
        }
        printf("semctl remove semaphore set OK\n");
        exit(EXIT_FAILURE);
    }
}

int main(void)
{
    int running=1;
    void *shared_memory=(void *)0;
    struct shared_use_st *shared_stuff;
    char buffer[BUFSIZ];
    int shmid;

    signal(SIGINT, my_func);

/***************************************************************/

    key_t semkey;
    if((semkey=ftok("/home", 1))<0)
    {
        printf("ftok failed\n");
        exit(EXIT_FAILURE);
    }
    printf("ftok ok, semkey=%d\n", semkey);

    if((semid=semget(semkey, 1, IPC_CREAT|0666))<0)
    {
        printf("semget failed\n");
        exit(EXIT_FAILURE);
    }
    printf("semget ok, semid = %d\n", semid);

    if((semctl(semid, 0, SETVAL, 1))<0)
    {
        printf("semctl set sermval failed\n");
        exit(EXIT_FAILURE);
    }
    printf("semctl set semval ok\n");

    struct sembuf p_op_buf, v_op_buf;
    p_op_buf.sem_num=0;
    p_op_buf.sem_op = -1;

/******************************************************************/

    /*创建共享内存*/
    shmid=shmget((key_t)1234,sizeof(struct shared_use_st),0666|IPC_CREAT);
    if(shmid==-1)
    {
        fprintf(stderr,"shmget failed\n");
        exit(EXIT_FAILURE);
    }

    /*映射共享内存*/
    shared_memory=shmat(shmid,(void *)0,0);
    if(shared_memory==(void *)-1)
    {
        fprintf(stderr,"shmat failed\n");
        exit(EXIT_FAILURE);
    }
    printf("Memory attached at %X\n",(int)shared_memory);

    /*让结构体指针指向这块共享内存*/
    shared_stuff=(struct shared_use_st *)shared_memory;

    /*循环的向共享内存中写数据，直到写入的为“end”为止*/
    while(running)
    {
/******************************************************************************/
        //获取信号量
        if(semop(semid, &p_op_buf, 1)<0)
        {
        printf("semop failed\n");
        exit(EXIT_FAILURE);
        }
        printf("shm2 get the semaphore\n");
/******************************************************************************/

        printf("Ener some text:");
        fgets(buffer,BUFSIZ,stdin);
        strncpy(shared_stuff->some_text,buffer,TEXT_SZ);
        shared_stuff->written_by_you=1;
        if(strncmp(buffer,"end",3)==0)
        {
            running=0;  //结束循环
        }

/*****************************************************************************/
        //释放信号量
        v_op_buf.sem_num = 0;
        v_op_buf.sem_op = 1;
        v_op_buf.sem_flg = 0;
        if(semop(semid, &v_op_buf, 1)<0)
        {
            printf("semop release semaphore failed\n");
            exit(EXIT_FAILURE);
        }
        printf("semop release semaphore ok\n");
/*****************************************************************************/
    }

    /*删除共享内存*/
    if(shmdt(shared_memory)==-1)
    {
        fprintf(stderr,"shmdt failed\n");
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

客户端:

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include "shm_com.h"

#include <sys/sem.h>

int main(void)
{
    int running=1;
    void *shared_memory=(void *)0;
    struct shared_use_st *shared_stuff;
    int shmid;
/***************************************************************/
    int pid,semid;
    key_t semkey;
    if((semkey=ftok("/home", 1))<0)
    {
        printf("ftok failed\n");
        exit(EXIT_FAILURE);
    }
    printf("ftok ok, semkey=%d\n", semkey);

    if((semid=semget(semkey, 0, 0))<0)
    {
        printf("semget failed\n");
        exit(EXIT_FAILURE);
    }
    printf("semget ok, semid = %d\n", semid);

    if((semctl(semid, 0, SETVAL, 1))<0)
    {
        printf("semctl set sermval failed\n");
        exit(EXIT_FAILURE);
    }
    printf("semctl set semval ok\n");

    struct sembuf p_op_buf, v_op_buf;
    p_op_buf.sem_num=0;
    p_op_buf.sem_op = -1;
    p_op_buf.sem_flg = 0;

/******************************************************************/
    /*创建共享内存*/
    shmid=shmget((key_t)1234,sizeof(struct shared_use_st),0666|IPC_CREAT);
    if(shmid==-1)
    {
        fprintf(stderr,"shmget failed\n");
        exit(EXIT_FAILURE);
    }

    /*映射共享内存*/
    shared_memory=shmat(shmid,(void *)0,0);
    if(shared_memory==(void *)-1)
    {
        fprintf(stderr,"shmat failed\n");
        exit(EXIT_FAILURE);
    }
    printf("Memory attached at %X\n",(int)shared_memory);

    /*让结构体指针指向这块共享内存*/
    shared_stuff=(struct shared_use_st *)shared_memory;

    /*控制读写顺序*/
    //shared_stuff->written_by_you=0;

    /*循环的从共享内存中读数据，直到读到“end”为止*/
    while(running)
    {
/*
       if(shared_stuff->written_by_you)
       {
         printf("You wrote:%s",shared_stuff->some_text);
           sleep(1);  //读进程睡一秒，同时会导致写进程睡一秒，这样做到读了之后再写
           shared_stuff->written_by_you=0;
           if(strncmp(shared_stuff->some_text,"end",3)==0)
           {
               running=0; //结束循环
           }
       }
*/
/******************************************************************************/
        //获取信号量
        if(semop(semid, &p_op_buf, 1)<0)
        {
        printf("semop failed\n");
        exit(EXIT_FAILURE);
        }
        printf("shm1 get the semaphore\n");
/*******************************************************************************/

        printf("You wrote:%s",shared_stuff->some_text);
        sleep(1);  //读进程睡一秒，同时会导致写进程睡一秒，这样做到读了之后再写

        if(strncmp(shared_stuff->some_text,"end",3)==0)
        {
           running=0; //结束循环
        }

/****************************************************************************/
        //释放信号量
        v_op_buf.sem_num = 0;
        v_op_buf.sem_op = 1;
        v_op_buf.sem_flg = 0;
        if(semop(semid, &v_op_buf, 1)<0)
        {
            printf("semop release semaphore failed\n");
            exit(EXIT_FAILURE);
        }
        printf("semop release semaphore ok\n");
/*****************************************************************************/

    }
/*******************************************************************************/

    /*删除共享内存*/
    if(shmdt(shared_memory)==-1)
    {
        fprintf(stderr,"shmdt failed\n");
        exit(EXIT_FAILURE);
    }
  exit(EXIT_SUCCESS);
}

以后的解决方案是先把那个信号量的程序由一个程序拆分成两个，彻底掌握信号量通信的过程。再来改造共享内存读写顺序。课程还要继续有机会再来解决吧！还一个实现上边 的方法参考这里。