通过共享内存 信号灯 通信（一） 一个读 一个写

两个进程 通过共享内存 信号灯 通信（一）
 实现最简单的功能 ：一个读 一个写 

write.c

//-------------------------------------
//两个进程通信 共享内存方式
//利用 信号灯 控制进程间的同步 和互斥
//2013-4-13
//-------------------------------------

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <sys/sem.h>
#include <errno.h>

#define N 64 // sizeof buf

union semun {
               int val; /* Value for SETVAL */
               struct semid_ds *buf; /* Buffer for IPC_STAT, IPC_SET */
               unsigned short *array; /* Array for GETALL, SETALL */
               struct seminfo *__buf; /* Buffer for IPC_INFO
                                           (Linux-specific) */
};


// struct of share memory
typedef struct share_memory
{
    char buf [N];
}sMemory;


//-----creat or open the memory----- return the shmid

int crop_memory(key_t key)
{
    int shmid;

    if(-1 == (shmid = shmget(key, sizeof(sMemory), IPC_CREAT | IPC_EXCL | 0666)))
    {
        if(errno == EEXIST)
        {
            shmid = shmget(key, sizeof(sMemory), 0666);
            //printf("the share memory has been created!\n");
            return shmid; // open success ,return the shmid
        }
        else
        {
            perror("shmget");
            return -1;
        }
    }
    // else creat success

    return shmid;
}

//------------- attached -----------

sMemory *
attached(int shmid)
{
    sMemory * add;
    if(NULL == (add = (sMemory *)shmat(shmid, NULL, 0)))        //NULL : the system chooses a suitable (unused)
    {                                        //address at which to attach the segment
        perror("shmat");
        return NULL;
    }

    return add;
}

//------- creat or open semaphore -------
int crop_semaphore(key_t key)
{
    int semid;

    if(-1 == (semid = semget(key, 2, 0666 | IPC_CREAT | IPC_EXCL )))
    {
        if(errno == EEXIST)
        {
            semid = semget(key, 2, 0666);
            //printf("the semaphore has been created !\n");
        }
        else{
            perror("semget");
            return -1;
        }
    }
    else{ // created semaphore success , inited
        union semun u; // 0 - read ; 1 - write

        u.val = 0;
        if(-1 == semctl(semid, 0, SETVAL, u))        // set 0 - read : 0
        {
            perror("semctl 1");
            return -1;
        }

        u.val = 1;
        if(-1 == semctl(semid, 1, SETVAL, u))    //set 1-write : 1
        {
            perror("semctl 2");
            return -1;
        }
    }

    return semid;
}

//------------- set_wsops------------
void set_wsops(struct sembuf * sops)
{
    sops->sem_num = 1;
    sops->sem_op = -1;
    sops->sem_flg = 0;
}

//------------- set_rsops------------
void set_rsops(struct sembuf * sops)
{
    sops->sem_num = 0;
    sops->sem_op = 1;
    sops->sem_flg = 0;
}

//----------sem_opration------------
int sem_opration(int semid, struct sembuf *sops, unsigned nsops)
{
    if(-1 == semop(semid, sops, nsops))
    {
        perror("semop");
        return -1;
    }
}

//------------- main ---------------

int main(void)
{
    key_t key;
    int shmid;
    int semid; // the identifier of semaphore
    sMemory * add; // the address of the attached shared memory
    struct sembuf sops;

    if(-1 == (key = ftok(".", 'l')))
    {
        perror("ftok");
        return -1;
    }

    shmid = crop_memory(key); // creat or open share memory
    add = attached(shmid);        // attached
    semid = crop_semaphore(key); //create or oen semaphore

    while(1)
    {
        set_wsops(&sops); // p option for semaphore 1 - write
        sem_opration(semid, &sops, 1);

        fgets(add->buf, sizeof(add->buf), stdin);
        //printf("%s", add->buf); // 若在此处读取共享内存中的数据，
                                    //读放也能再读取。说明读操作没有清空内存！！！

        set_rsops(&sops); // v option for semaphore o - read
        sem_opration(semid, &sops, 1);
    }

    return 0;
}

read.c

//-------------------------------------
//两个进程通信 共享内存方式
//利用 信号灯 控制进程间的同步 和互斥
//2013-4-13
//-------------------------------------

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <sys/sem.h>
#include <errno.h>

#define N 64 // sizeof buf

union semun {
               int val; /* Value for SETVAL */
               struct semid_ds *buf; /* Buffer for IPC_STAT, IPC_SET */
               unsigned short *array; /* Array for GETALL, SETALL */
               struct seminfo *__buf; /* Buffer for IPC_INFO
                                           (Linux-specific) */
};


// struct of share memory
typedef struct share_memory
{
    char buf [N];
}sMemory;


//-----creat_memory----- return the shmid

int crop_memory(key_t key)
{
    int shmid;

    if(-1 == (shmid = shmget(key, sizeof(sMemory), IPC_CREAT | IPC_EXCL | 0666)))
    {
        if(errno == EEXIST)
        {
            shmid = shmget(key, sizeof(sMemory), 0666);
            //printf("the share memory has been created!\n");
            return shmid; // open success ,return the shmid
        }
        else
        {
            perror("shmget");
            return -1;
        }
    }
    // else creat success

    return shmid;
}

//------------- attached -----------

sMemory *
attached(int shmid)
{
    sMemory * add;
    if(NULL == (add = (sMemory *)shmat(shmid, NULL, 0)))        //NULL : the system chooses a suitable (unused)
    {                                        //address at which to attach the segment
        perror("shmat");
        return NULL;
    }

    return add;
}

//------- creat or open semaphore -------
int crop_semaphore(key_t key)
{
    int semid;

    if(-1 == (semid = semget(key, 2, 0666 | IPC_CREAT | IPC_EXCL )))
    {
        if(errno == EEXIST)
        {
            semid = semget(key, 2, 0666);
            //printf("the semaphore has been created !\n");
        }
        else{
            perror("semget");
            return -1;
        }
    }
    else{ // created semaphore success , inited
        union semun u; // 0 - read ; 1 - write

        u.val = 0;
        if(-1 == semctl(semid, 0, SETVAL, u))    // set 0 - read : 0
        {
            perror("semctl 1");
            return -1;
        }

        u.val = 1;
        if(-1 == semctl(semid, 1, SETVAL, u))    //set 1-write : 1
        {
            perror("semctl 2");
            return -1;
        }
    }

    return semid;
}

//------------- set_wsops------------
void set_wsops(struct sembuf * sops)
{
    sops->sem_num = 1;
    sops->sem_op = 1;
    sops->sem_flg = 0;
}

//------------- set_rsops------------
void set_rsops(struct sembuf * sops)
{
    sops->sem_num = 0;
    sops->sem_op = -1;
    sops->sem_flg = 0;
}

//----------sem_opration------------
int sem_opration(int semid, struct sembuf *sops, unsigned nsops)
{
    if(-1 == semop(semid, sops, nsops))
    {
        perror("semop");
        return -1;
    }
}

//------------- main ---------------

int main(void)
{
    key_t key;
    int shmid;
    int semid; // the identifier of semaphore
    sMemory * add; // the address of the attached shared memory
    struct sembuf sops;

    if(-1 == (key = ftok(".", 'l')))
    {
        perror("ftok");
        return -1;
    }

    shmid = crop_memory(key); // creat or open share memory
    add = attached(shmid);        // attached
    semid = crop_semaphore(key); //create or oen semaphore

    while(1)
    {
        set_rsops(&sops); // p option for semaphore 1 - read
        sem_opration(semid, &sops, 1);

        //fgets(add->buf, sizeof(add->buf), stdin);
        printf("%s", add->buf);

        set_wsops(&sops); // v option for semaphore o - write
        sem_opration(semid, &sops, 1);
    }

    return 0;
}

运行截图


注意：此程序没有包含共享内存的删除功能，需要人为删除。否则下次再启动程序时无法再向共享内存中写入数据。
删除共享内存方法
一： 输入命令 ipcs


二：输入 ipcrm -m shmid  （此处的shmid是 如上图中的 262144)
三：输入ipcrm -s semid （此处的semid 是 上图中的 262144）
完毕