sem_writer.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 write_data_base()
{
	int number;
	int fd;
	int n;

	srand(time(0));
	number = rand()%100;
	printf("writer:%d	%d\n",getpid(),number);
	if(file_creat == 0) {
		if((fd = open(FILE_NAME,O_CREAT | O_RDWR | O_EXCL,S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) < 0) {
			if((fd = open(FILE_NAME,O_RDWR)) < 0) {
				perror("open file fail\n");
				exit(1);
			}
		}
		file_creat = 1;
	} else {
		if((fd = open(FILE_NAME,O_RDWR)) < 0) {
			perror("open file fail\n");
			exit(1);
		}
	}
	if((n = write(fd,&number,sizeof(int)) < sizeof(int))) {
		perror("write error\n");
		exit(1);
	}
	close(fd);
	srand(time(0));
	sleep(rand()%10+1);
}



int main()
{

	int semid_rc,semid_mutex,semid_db;

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

	while(1) {
		V(&semid_db);
		/*do work*/
		write_data_base();
		P(&semid_db);
	}
	return 0;
}