fcntl_write.c

《嵌入式Linux应用程序开发详解》一书的源代码之第六章

#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>

void lock_set(int fd, int type)
{
	struct flock lock;
	lock.l_whence = SEEK_SET;//¸³ֵlock½ṹÌ
	lock.l_start = 0;
	lock.l_len =0;
	while(1){
		lock.l_type = type;
		if((fcntl(fd, F_SETLK, &lock)) == 0){
		if( lock.l_type == F_RDLCK )
			printf("read lock set by %d\n",getpid());
		else if( lock.l_type == F_WRLCK )
			printf("write lock set by %d\n",getpid());
		else if( lock.l_type == F_UNLCK )
			printf("release lock by %d\n",getpid());
		return;
		}
		fcntl(fd, F_GETLK,&lock);
		if(lock.l_type != F_UNLCK){
			if( lock.l_type == F_RDLCK ) 
				printf("read lock already set by %d\n",lock.l_pid);
			else if( lock.l_type == F_WRLCK )
				printf("write lock already set by %d\n",lock.l_pid);
			getchar();
		}
	}
}

int main(void)
{
	int fd;
	fd=open("hello",O_RDWR | O_CREAT, 0666);
	if(fd < 0){
		perror("open");
		exit(1);
	}
	lock_set(fd, F_WRLCK);
	getchar();
	lock_set(fd, F_UNLCK);
	getchar();
	close(fd);
	exit(0);
}