lock3.c

#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>

const char *test_file = "/tmp/test.lock";

int main()
{
	int file_desc;
	int byte_count;
	char *byte_to_write = "A";
	struct flock region_1;
	struct flock region_2;
	int res;

	file_desc=open(test_file,O_RDWR| O_CREAT,0666);
	if (!file_desc) {
		fprintf(stderr,"Unable to open %s for read/write\n", test_file);
		exit(EXIT_FAILURE);
	}

	for(byte_count=0; byte_count <100;byte_count++){
		(void)write(file_desc,byte_to_write,1);
	}

	region_1.l_type=F_RDLCK;
	region_1.l_whence=SEEK_SET;
	region_1.l_start=10;
	region_1.l_len=20;

	region_2.l_type=F_WRLCK;
	region_2.l_whence=SEEK_SET;
	region_2.l_start=40;
	region_2.l_len=10;

	printf("Process %d locking file\n",getpid());
	res=fcntl(file_desc,F_SETLK,&region_1);
	if(res==-1) fprintf(stderr,"Failed to lock region 1\n");
	res=fcntl(file_desc,F_SETLK,&region_2);
	if(res==-1) fprintf(stderr, "Failed to lock region 2\n");
	sleep(60);

	printf("Process %d closing file\n",getpid());
	close(file_desc);
	exit(EXIT_SUCCESS);

}