Sweden-Number/ipc/shm_semaph.c

141 lines
3.5 KiB
C

/***************************************************************************
* Copyright 1995, Technion, Israel Institute of Technology
* Electrical Eng, Software Lab.
* Author: Michael Veksler.
***************************************************************************
* File: shm_semaph.c
* Purpose: Handle semaphores for shared memory operations.
***************************************************************************
*/
#ifdef CONFIG_IPC
#define inline inline
#include <assert.h>
#include <unistd.h>
#include <sys/sem.h>
#include <errno.h>
#include "debug.h"
#include "shm_semaph.h"
DEFAULT_DEBUG_CHANNEL(sem)
#define SEM_READ 0
#define SEM_WRITE 1
/* IMPORTANT: Make sure that killed process will not lock everything.
* If possible, restrict usage of these functions.
*/
void shm_read_wait(shm_sem semid)
{
struct sembuf sop[2];
int ret;
TRACE(sem,"(%d)\n",semid);
sop[0].sem_num=SEM_READ;
sop[0].sem_op=1; /* add this read instance */
sop[0].sem_flg=SEM_UNDO; /* undo in case process dies */
sop[1].sem_num=SEM_WRITE;
sop[1].sem_op=0; /* wait until no writing instance exists */
sop[1].sem_flg=SEM_UNDO;
do {
ret=semop (semid,sop , 2);
} while (ret<0 && errno==EINTR); /* interrupted system call? */
if (ret<0)
WARN(sem,"(semid=%d,errno=%d): Failed semaphore lock for read\n",
semid, errno);
}
void shm_write_wait(shm_sem semid)
{
struct sembuf sop[3];
int ret;
TRACE(sem,"(%d)\n",semid);
sop[0].sem_num=SEM_READ;
sop[0].sem_op=0; /* wait until no reading instance exist */
sop[0].sem_flg=SEM_UNDO;
sop[1].sem_num=SEM_WRITE;
sop[1].sem_op=1; /* writing is in progress - disable read */
sop[1].sem_flg=SEM_UNDO; /* undo if process dies */
sop[2].sem_num=SEM_READ;
sop[2].sem_op=1; /* disable new writes */
sop[2].sem_flg=SEM_UNDO;
do {
ret=semop (semid,sop , 3);
} while (ret<0 && errno==EINTR); /* interrupted system call? */
if (ret<0) /* test for the error */
WARN(sem,"(semid=%d,errno=%d): Failed semaphore lock for write\n",
semid, errno);
}
void shm_write_signal(shm_sem semid)
{
struct sembuf sop[2];
int ret;
TRACE(sem,"(%d)\n",semid);
sop[0].sem_num=SEM_READ;
sop[0].sem_op=-1;
sop[0].sem_flg=IPC_NOWAIT | SEM_UNDO; /* no reason to wait */
sop[1].sem_num=SEM_WRITE;
sop[1].sem_op=-1;
sop[1].sem_flg=IPC_NOWAIT | SEM_UNDO; /* no reason to wait */
do {
ret=semop (semid,sop , 2);
} while (ret<0 && errno==EINTR); /* interrupted system call? */
if (ret<0) /* test for the error */
WARN(sem,"(semid=%d,errno=%d): Failed semaphore unlock for write\n",
semid, errno);
}
void shm_read_signal(shm_sem semid)
{
struct sembuf sop[2];
int ret;
TRACE(sem,"(%d)\n",semid);
sop[0].sem_num=SEM_READ;
sop[0].sem_op=-1;
sop[0].sem_flg=IPC_NOWAIT | SEM_UNDO; /* no reason to wait */
do {
ret=semop (semid,sop , 1);
} while (ret<0 && errno==EINTR); /* interrupted system call? */
if (ret<0) /* test for the error */
WARN(sem,"(semid=%d,errno=%d): Failed semaphore unlock for read\n",
semid, errno);
}
void shm_sem_init(shm_sem *sptr)
{
shm_sem semid;
union semun arg;
semid=semget (IPC_PRIVATE, 2, 0700 | IPC_CREAT);
arg.val=0;
semctl (semid, 0, SETVAL, arg);
semctl (semid, 1, SETVAL, arg);
*sptr=semid;
}
void shm_sem_done(shm_sem *semptr)
{
union semun arg;
semctl (*semptr, 0, IPC_RMID , arg);
semctl (*semptr, 1, IPC_RMID , arg);
*semptr= -1;
}
#endif /* CONFIG_IPC */