p11-17.c

SUN Solaris8平台下进程间通信

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
int open_semaphore_set( key_t, int);
void init_a_semaphore( int, int, int);
int rm_semaphore(int);
int semaphore_P(int);
int semaphore_V(int sem_id);
int main(int argc, char *argv[])
{
    int sem_id;
    int i, creat = 0;
    int pause_time;
    char *cp;
    /*以进程ID作为随机数种子 */
    srand((unsigned int)getpid());
    /* 打开/创建仅一个信号量的集合*/              
    sem_id = open_semaphore_set((key_t)1234, 1);
    if (argc > 1 && strcmp(argv[1],"1")) {  /* 负责创建和删除信号量集合 */
        /* 设置第一个信号量的初值为1 */
        init_a_semaphore(sem_id, 0, 1);
        creat = 1;                
        sleep(2);                          
    }
    for (i = 0; i < argc; i++) { 
        cp = argv[i];       
        if (!semaphore_P(sem_id)) exit(EXIT_FAILURE);
        /* 关键区开始 */
       printf("process %d:",getpid()); 
       fflush(stdout);
       while(*cp){        
           printf("%c",*cp);
           fflush(stdout);
           pause_time = rand() % 3;
           sleep(pause_time);
           cp++;
        }
        printf("\n");
        /* 关键区结束 */        
        if (!semaphore_V(sem_id)) exit(EXIT_FAILURE);
        pause_time = rand() % 2;
        sleep(pause_time);
    }    
    printf("\n%d - finished\n", getpid());
    if (creat == 1) {    
        sleep(10);
        rm_semaphore(sem_id);
    }
    exit(EXIT_SUCCESS);
}
/* P操作--企图进入一关键区 */
int semaphore_P(int sem_id)
{
    struct sembuf sb;
    sb.sem_num = 0;
    sb.sem_op = -1;          /* P操作－信号量值减少 */
    sb.sem_flg = SEM_UNDO;   /* 如果死亡，解除信号量请求*/

    if (semop(sem_id, &sb, 1) == -1){
        fprintf(stderr,"semaphore_P failed\n");
        return(0);
    }
    return(1);
}
/* V操作--离开关键区 */
int semaphore_V(int sem_id)
{
    struct sembuf sb;
    sb.sem_num = 0;
    sb.sem_op = 1;           /* V操作－信号量值增加 */
    sb.sem_flg = SEM_UNDO;   /* 如果死亡，解除信号量请求*/

    if (semop(sem_id, &sb, 1) == -1){
        fprintf(stderr,"semaphore_V failed\n");
        return(0);
    }
    return(1);
}

/* 说明semun结构 */
union semun {
   int val;
   struct semid_ds *buf;
   unsigned short *array;
};
/* 获得指定的信号量之值 */
int get_sem_val( int sid, int semnum )
{
    return( semctl(sid, semnum, GETVAL, 0));
}
/* 给指定的信号量赋初值 */
void init_a_semaphore( int sid, int semnum, int initval)
{
    union semun semopts;    
    semopts.val = initval;
    semctl( sid, semnum, SETVAL, semopts);
}
/* 给指定的信号量集合赋初值 */
void init_all_semaphore( int sid, int val_array[])
{
    union semun semopts; 
    semopts.array = val_array;
    semctl( sid, 0, SETALL, semopts);
}
/* 改变信号量集合的访问权限,权限参数必须是形如"660"的字符串 */
int changemode(int sid, char *mode)
{
    int rc;
    union semun semopts;    
    struct semid_ds mysemds;
    /* 注意，应先使semopts.buf 指向我们自己定义的缓冲区! */
    semopts.buf = &mysemds;
    /* 获得内部数据结构的当前值 */
    if ((rc = semctl(sid, 0, IPC_STAT, semopts)) == -1)
        return -1;
    /* 改变访问权限 */
    sscanf(mode, "%o", &semopts.buf->sem_perm.mode);
    /* 更新内部数据结构 */
    return(semctl(sid, 0, IPC_SET, semopts));
}
/* 删除指定的信号量集合 */
int rm_semaphore(int sid)
{
    return(semctl(sid, 0, IPC_RMID,0));
}

int open_semaphore_set( key_t keyval, int numsems )
{
     int     sid;
     if (!numsems)
         return(-1);
     if((sid = semget( keyval, numsems, IPC_CREAT | 0660 )) == -1)
         return(-1);
     else
         return(sid);
}