Date: Sat, 3 Aug 1996 19:37:16 -0700 (PDT) From: Archie Cobbs <archie@whistle.com> To: freebsd-hackers@freebsd.org Subject: flock() broken on certain files Message-ID: <199608040237.TAA05031@bubba.whistle.com>
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How hard would it be to get flock() to work on a fifo? Right now
it seems that it doesn't... could someone else verify this?
It seems that fifo's are exactly the kind of thing you would want
to be able to set a lock on, e.g., when multiple processes are writing
to it.
Here's a sample program:
/* foo.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <err.h>
int
main()
{
int fd;
FILE *fp;
fd = open("fifo", O_WRONLY, O_EXLOCK | O_NONBLOCK);
if (fd < 0)
{
warn("pid %lu: open", getpid());
exit(1);
}
if ((fp = fdopen(fd, "a")) == NULL)
{
warn("pid %lu: fdopen", getpid());
exit(1);
}
warnx("pid %lu opened fifo", getpid());
sleep(5);
fprintf(fp, "pid %lu reporting 1\n", getpid());
fflush(fp);
sleep(5);
fprintf(fp, "pid %lu reporting 2\n", getpid());
fflush(fp);
sleep(5);
fprintf(fp, "pid %lu reporting 3\n", getpid());
fflush(fp);
warnx("pid %lu exiting", getpid());
return(0);
}
The open()'s are not being blocked, even though O_EXLOCK is specified:
$$ mkfifo fifo
csh: cat fifo > /dev/null &
[3] 5017
$$ ./foo &
[4] 5018
foo: pid 5018 opened fifo
$$ ./foo &
[5] 5019
foo: pid 5019 opened fifo
$$ wait
foo: pid 5018 exiting
[4] Done ./foo
foo: pid 5019 exiting
[5] Done ./foo
[3] Done cat fifo > /dev/null
$$
-Archie
___________________________________________________________________________
Archie L. Cobbs, archie@whistle.com * Whistle Communications Corporation
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