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sem182.c
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sem182.c
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#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdio.h>
#include <errno.h>
#if __STDC__
# include <stdlib.h>
#endif
#define SEM_NR 1
#if __STDC__
int semrm(int semid)
#else
int semrm(semid)
int semid;
#endif
{
return semctl(semid, SEM_NR, IPC_RMID, 0);
}
#if __STDC__
int seminit(key_t key, int semperm, int initval)
#else
int seminit(key, semperm, initval)
key_t key;
int semperm, initval;
#endif
{
#if !defined(__GNU_LIBRARY__) || defined(_SEM_SEMUN_UNDEFINED)
union semun {
int val; /* value for SETVAL */
struct semid_ds *buf; /* buffer for IPC_STAT, IPC_SET */
unsigned short int *array; /* array for GETALL, SETALL */
};
#endif
int semid;
union semun semarg;
semarg.val = initval;
if ( (semid = semget (key, SEM_NR, IPC_CREAT | IPC_EXCL | (semperm & 0666)))
< 0)
return(-1);
/* Initialize Semaphore */
if (semctl (semid, 0, SETVAL, semarg) < 0) {
int semctlerror = errno; /* save error condition */
(void) semrm(semid);
errno = semctlerror; /* restore error condition for user */
return(-1);
}
return(semid);
}
#if __STDC__
int semgrab(key_t key)
#else
int semgrab(key)
key_t key;
#endif
{
return semget (key, SEM_NR, 0);
}
/* Dijkstra' s V(s) [signal] */
#if __STDC__
int V(int semid)
#else
int V(semid)
int semid;
#endif
{
struct sembuf semp[1];
semp[0].sem_num = 0;
semp[0].sem_op = 1;
semp[0].sem_flg = 0;
return(semop(semid, &semp[0], 1));
}
/* Dijkstra' s P(s) [wait] */
#if __STDC__
int P(int semid)
#else
int P(semid)
int semid;
#endif
{
struct sembuf semp[1];
semp[0].sem_num = 0;
semp[0].sem_op = -1;
semp[0].sem_flg = 0;
return(semop(semid, &semp[0], 1));
}