用信号量同步生产者消费者的问题

[elated]

用信号量同步生产者消费者。
大家帮我看看这个程序错在哪了。
为什么信号量为0时没有阻塞进程？

还有sembuf结构有个sem_flag成员， 那个SEM_UNDO位是做什么的？我看apue没看明白。

#include "apue.h"
#include <assert.h>
#include <sys/sem.h>
#include <sys/ipc.h>
#include <sys/wait.h>

#define N 10
#define MUTEX 0
#define FULL 1
#define EMPTY 2

typedef union semun {
	int		val;
	struct semid_ds	*buf;
	unsigned short	*array;
};

int		num = 0;

int init_sem(int, int , int);
int up(int, int);
int down(int, int);
void producer(int);
void consumer(int);

int main (int argc, char *argv[])
{
	int	semid;
	pid_t	pid1, pid2;

	if ((semid = semget(IPC_PRIVATE, 3, 0660)) < 0)
		err_sys("semget error");

	init_sem(semid, MUTEX, 1);		/* mutex */
	init_sem(semid, FULL, 0);		/* full */
	init_sem(semid, EMPTY, N);		/* empty */

	if ((pid1 = fork()) < 0 ) {
		err_sys("fork error");
	} else if( pid1 == 0) {
		producer(semid);		/* child1 producer */
	} else {
		if((pid2 = fork()) < 0 ){
			err_sys("fork error");
		} else if ( pid2 == 0) {	/* child2 consumer */
			consumer(semid);
		} else	{
		if (waitpid(pid1, NULL, 0) != pid1 || 
			waitpid(pid2, NULL, 0 ) != pid2)
			err_sys("waitpid error");
		}
	}

	if (semctl(semid, 0, IPC_RMID) < 0)
		err_sys("semctl error");

	exit(0);
}

int init_sem(int semid, int semnum, int val)
{
	union	semun unarg;

	unarg.val = val;
	if (semctl(semid, semnum, SETVAL, unarg) < 0)
		err_sys("semctl error");
	return 0;
}

int up(int semid, int semnum)
{
	struct sembuf	semoparray[1];
	
	semoparray[0].sem_num = semnum;
	semoparray[0].sem_op = 1;
	semoparray[0].sem_flg = 0;

	if (semop(semid, semoparray, 1) < 0)
		err_sys("semop error");
	
	return 0;
}

int down(int semid, int semnum)
{	
	struct sembuf	semoparray[1];

	semoparray[0].sem_num = semnum;
	semoparray[0].sem_op = -1;
	semoparray[0].sem_flg = 0; /* IPC_NOWAIT, SEM_UNDO(这个宏有什么作用？） */
	
	if (semop(semid, semoparray, 1) < 0)
		err_sys("semop error");
	
	return 0;
}

void producer(int semid)
{
	int i = 1000;
	int sem1, sem2;
	while (i--) {
		assert((sem1 = semctl(semid, EMPTY, GETVAL, NULL))<= 10);
		assert((sem2 = semctl(semid, FULL, GETVAL, NULL)) >= 0);	
		down(semid, EMPTY);
		down(semid, MUTEX);
		num++;
		printf("producer num = %i \n", num);
		printf("EMPTY = %i ; FULL =  %i ; \n", sem1, sem2);
		up(semid, MUTEX);
		up(semid, FULL);
	}

	exit(0);
}

void consumer(int semid)
{
	int i = 1000;
	int sem1, sem2;
	while (i--) {
		assert((sem1 = semctl(semid, EMPTY, GETVAL, NULL))<= 10);
		assert((sem2 = semctl(semid, FULL, GETVAL, NULL)) >= 0);	
		down(semid, FULL);
		down(semid, MUTEX);
		num--;
		printf("consumer num = %i \n", num);
		printf("EMPTY = %i ; FULL =  %i ; \n", sem1, sem2);
		up(semid, MUTEX);
		up(semid, MUTEX);
		up(semid, EMPTY);
	}

	exit(0);
}

[steptodream]

不会 帮顶

[xsz19880101]

#include"apue.h" 与#include<stdio.h> 的区别。
查找头文件的路径不一样，一个是本地，一个是系统标准头文件路径 ，也就是先从当前目录搜索指定文件，如果没有，再从系统标准路径搜索.

程序中最后多写了个up(semid, MUTEX);

[elated]

up

[elated]

多写了个up(semid, MUTEX);

[elated]

up

[goooglemister]

up