sem_reader.c

这是自己写的一个关于经典ipc问题－读者写者的实现。（用信号量实现）

#include <sys/types.h>
#include <sys/sem.h>
#include <sys/ipc.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include "sem_func.h"

#define FILE_NAME "buffer"

int file_creat;


void read_data_base()
{
	int fd;
	int number;
	
	if((fd = open(FILE_NAME,O_RDONLY)) < 0) {
		perror("open file fail\n");
		exit(1);
	}
	if(read(fd,&number,sizeof(int)) < 0) {
		perror("read error\n");
		exit(1);
	}
	close(fd);
	printf("reader:%d	%d\n",getpid(),number);
	srand(time(0));
	sleep(rand()%3+1);
}






int main()
{
	int semid_rc,semid_mutex,semid_db;
	int val;
	union semun arg;

	init(&semid_rc,0,LOCKFILE_RC);
	init(&semid_db,1,LOCKFILE_DB);
	init(&semid_mutex,1,LOCKFILE_MUTEX);

	while(1) {
		V(&semid_mutex);
		P(&semid_rc);
		val = semctl(semid_rc,0,GETVAL,arg);
		if(val == 1)
			V(&semid_db);
		P(&semid_mutex);
		/*do work here*/
		read_data_base();
		V(&semid_mutex);
		V(&semid_rc);
		val = semctl(semid_rc,0,GETVAL,arg);
		if(val == 0)
			P(semid_db);
		P(semid_mutex);
	}

	return 0;
}