Re: [KFUG] POSIX named semaphore

[Pyun YongHyeon <yongari@xxxxxxxxxxx>]

On Mon, May 17, 2004 at 03:22:15PM +0900, Seung-joo Lee wrote:
 > > ....
 > > sem_t *mutex;
 > > /* mutex = sem_open (SEM_NAME, O_CREAT | O_EXCL, FILE_MODE, 1); */
 > > /* mutex = sem_open (SEM_NAME, O_CREAT | O_EXCL); */
 > > mutex = sem_open (SEM_NAME, O_CREAT);
 > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 > > POSIX sem_open(3)을 살펴보세요.
 > > O_CREAT Create the semaphore if it does not already exist.
 > > The third argument to the call to sem_open() must be of type
 > > mode_t and specifies the mode for the semaphore. Only the
 > > S_IWUSR, S_IWGRP, and S_IWOTH bits are examined; it is not pos-
 > > sible to grant only ``read'' permission on a semaphore. The
 > > mode is modified according to the process's file creation mask;
 > > see umask(2).
 > > The fourth argument must be an unsigned int and specifies the
 > > initial value for the semaphore, and must be no greater than
 > > SEM_VALUE_MAX.
 > > if ( mutex == SEM_FAILED )
 > > ....
 > 네, 제가 미처 그 부분을 읽지를 못했습니다.
 > 그런데 그렇게 변경을 하고 해봐도 결과는 같게 나오더군요.
 > ( mutex = sem_open ("/tmp/mysem", O_CREAT, S_IWUSR, 1); )
 > 혹시 위 소스를 컴파일 해 보신 다른 분들은 되시나요?

#include <fcntl.h>
#include <semaphore.h>
#include <stdio.h>
#include <errno.h>

int
main(void)
{
        sem_t *s;
	int val;

        s = sem_open("/sem_test", O_CREAT, 0777, 5);   
        if (s == SEM_FAILED){
                printf("%s\n", strerror(errno));
		return (1);
	}
	sem_getvalue(s, &val);
	printf("val = %d\n", val);
	sem_close(s);
	return (0);
}

커널에 'options P1003_1B_SEMAPHORES'가  없다면 sem(4)을 커널
모듈로 load하면 됩니다. 
#cd /usr/src/sys/modules/sem
#make && make install && make load
-- 
Pyun YongHyeon <http://www.kr.freebsd.org/~yongari>
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