Attachment 161406 Details for Bug 252000 – Get an exclusive lock on a file

Get an exclusive lock on a file

fcntlwritelock.c (text/x-csrc), 1.24 KB, created by Matt Brookover on 2007-08-15 21:25:56 UTC

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Creator: Matt Brookover

Created: 2007-08-15 21:25:56 UTC

Size: 1.24 KB

patch

obsolete

>#include <stdio.h>
>#include <unistd.h>
>#include <sys/types.h>
>#include <sys/stat.h>
>#include <fcntl.h>
>#include <string.h>
>#include <time.h>
>#include <errno.h>
>
>int writelock(char *filename)
>{
>	int fd;
>	struct flock mylock;
>
>	if ((fd=open(filename,O_CREAT|O_RDWR,S_IRUSR|S_IWUSR|S_IRGRP))==-1)
>	{
>		fprintf (stderr,"Could not open %s:",filename);
>		perror ("");
>		exit(1);
>	}
>
>	mylock.l_type=F_WRLCK;
>	mylock.l_len=0;		/*lock entire file */
>	mylock.l_whence=SEEK_SET;
>	mylock.l_start=0;
>/*
>** F_SETLKW seems to work on GFS under light load
>** looping over F_SETLK will fail with errno operation not permitted
>*/
>	while (fcntl(fd,F_SETLK,&mylock) == -1)
>	{
>		if (errno!=EAGAIN)
>		{
>			fprintf (stderr,"Could not get write lock on %s errno=%d:",filename,errno);
>			perror ("");
>			exit(1);
>		}
>		printf ("%s locked, trying again\n",filename);
>	}
>
>	printf ("Have write lock, hit return to free write lock on %s and exit\n",filename);
>	fgetc(stdin);
>
>	mylock.l_type=F_UNLCK;
>	mylock.l_len=0;		/*lock entire file */
>	mylock.l_whence=SEEK_SET;
>	mylock.l_start=0;
>	if (fcntl(fd,F_SETLK,&mylock) == -1)
>	{
>		fprintf (stderr,"Could unlock %s:",filename);
>		perror ("");
>		exit(1);
>	}
>
>	close(fd);
>}
>
>main(int argc, char *argv[])
>{
>	int fd;
>	int i;
>	fd=writelock(argv[1]);
>}
>

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Attachments on bug 252000: 161204 | 161205 | 161405 | 161406