On Sat, Nov 06, 1999 at 12:50:16AM +0100, Ollivier Robert wrote:
A child process seems to be able to let go of a parent's lock on
4.0 by closing a file discriptor, the same doesn't seem to be true
on 3.3.
For example, if you try to run two copies of the included program
as on 3.3, you get a resource unavailable message.
12:57:walton 6% ./lockf_test /tmp/blah 5 &
[1] 2453
13:01:walton 7% ./lockf_test /tmp/blah 5
Unable to open file: Resource temporarily unavailable
13:01:walton 8%
[1] Done ./lockf_test /tmp/blah 5
On 4.0 two run concurrently quite happily:
12:54:gonzo 65% ./lockf_test /tmp/blah 5 &
[1] 943
13:02:gonzo 66% ./lockf_test /tmp/blah 5
[1] Done ./lockf_test /tmp/blah 5
13:02:gonzo 67%
If you remove the "if(fork==0){close(fd);}" it two copies will not
run concurrently on 4.0. I'm not sure which behavior is correct, but
I suspect the 3.0 behavior is, 'cos /usr/bin/lockf is broken by
this on 4.0.
David.
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc,char **argv)
{
int fd;
if( argc != 3 ) {
fprintf(stderr, "Usage: %s filename seconds\n", argv[0]);
exit(1);
}
if( (fd = open(argv[1], O_RDONLY|O_CREAT|O_NONBLOCK|O_EXLOCK,0666)) == -1 ) {
perror("Unable to open file");
exit(2);
}
if( fork() == 0 ) {
close(fd);
}
sleep(atoi(argv[2]));
exit(0);
}
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