Linux _sem 信号量 V_P

#include <stdlib.h>
#include <stdio.h>

int main(void)
{
int i;

for (i=0; i<5; i++) {

/* ƒ£ƒ‚¡ŸΩÁ«¯----begin */
printf("Process(%d) In\n", getpid());
sleep(1);
printf("Process(%d) Out\n", getpid());
/* ƒ£ƒ‚¡ŸΩÁ«¯----end */

sleep(1);
}

return 0;
}

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

#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED)
#else
union semun {
int val;
struct semid_ds *buf;
unsigned short int *array;
struct seminfo *__buf;
};
#endif

static sem_initial(int semid)
{
int ret;

union semun semun;
semun.val = 1;
ret = semctl(semid, 0, SETVAL, semun);
if (ret == -1) {
fprintf(stderr, "semctl failed!\n");
}

return ret;
}

static int  sem_p(int semid)
{
int ret;

struct sembuf sembuf;
sembuf.sem_op = -1;
sembuf.sem_num = 0;
sembuf.sem_flg = SEM_UNDO;
ret = semop(semid, &sembuf, 1);
if (ret == -1) {
fprintf(stderr, "sem_p failed!\n");
}

return ret;
}

static int  sem_v(int semid)
{
int ret;

struct sembuf sembuf;
sembuf.sem_op = 1;
sembuf.sem_num = 0;
sembuf.sem_flg = SEM_UNDO;
ret = semop(semid, &sembuf, 1);
if (ret == -1) {
fprintf(stderr, "sem_v failed!\n");
}

return ret;
}

int main(int argc, char* argv[])
{
int i;
int ret;
int semid;

/* ªÒ»°–≈∫≈¡ø */
semid = semget((key_t)1234, 1, 0666 | IPC_CREAT);
if (semid == -1) {
printf("semget failed!\n");
exit(1);
}

/* ≥ı ºªØ–≈∫≈¡ø */
if (argc > 1) {
ret = sem_initial(semid);
if (ret == -1) {
exit(1);
}
}

for (i=0; i<5; i++) {

if (sem_p(semid) == -1) {
exit(1);
}

/* ƒ£ƒ‚¡ŸΩÁ«¯----begin */
printf("Process(%d) In\n", getpid());
sleep(1);
printf("Process(%d) Out\n", getpid());
/* ƒ£ƒ‚¡ŸΩÁ«¯----end */

if (sem_v(semid) == -1) {
exit(1);
}

sleep(1);
}

/* …æ≥˝–≈∫≈¡ø */

return 0;
}