0
#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
int main()
{
key_t key, k, shmid;
int ret, semid, i = 0;
struct sembuf op[1];
void *shmptr = (void *) 0;
union semun {
int val;
struct senid_ds *buf;
unsigned short *array;
};
union semun arg;
/* Creating a shared memory */
k = ftok(".", 1);
if (-1 == k) {
perror("\n ftok \n");
return 1;
}
shmid = shmget(k, 1000, IPC_CREAT | 0744);
if (-1 == shmid) {
perror("\n Shared memory creation failed \n");
return 2;
}
shmptr = shmat(shmid, (void *) 0, 0);
if (NULL == shmptr) {
perror("\n Process cant attach to shared memory segment! \n");
return 3;
}
/* Creating semaphore */
key = ftok(".", 4);
if (-1 == key) {
perror("\n ftok \n");
return 4;
}
#if 0
semid = semget(key, 1, IPC_CREAT);
#else
semid = semget(key, 1, 0);
#endif
if (-1 == semid) {
perror("\n Cannot create semaphore \n");
return 5;
}
#if 0
arg.val = 1;
ret = semctl(semid, 0, SETVAL, arg);
printf("\n ret : %d \n", ret);
#endif
op[0].sem_num = 0;
op[0].sem_op = -1;
op[0].sem_flg = SEM_UNDO;
ret = semop(semid, op, 1);
// printf("\n ret : %d semop : %d\n",ret,op[0].sem);
printf("\n Process 1 locked sem1 \n");
/* Do Operation on shared resource */
while (i < 4) {
strcpy((char*) shmptr, "BDC");
printf("\n %s \n", (char *) shmptr);
sleep(2);
printf("\n After sleep \n");
i++;
shmptr++;
}
op[0].sem_op = 1;
ret = semop(semid, op, 1);
printf("\n Process A unlocked sem1 \n");
return 0;
}
我試過了一個鎖定共享內存段的示例程序。我嘗試了同一個程序的兩個實例。查看信號量是否正確鎖定。但是,上面的程序總是允許其他進程在process1已被鎖定時使用共享內存。無法確定錯誤在哪裏。在共享內存中鎖定信號量問題
你看到什麼讓你認爲它不工作?你做了什麼來試圖找出錯誤? – wallyk
它必須是代碼中的'Yoda Conditions' –
@wallyk:2個進程不同步訪問共享段 – Angus