Re: My way to check if a progam is already running

On a sunny day (Mon, 25 Jun 2007 10:30:28 +0200) it happened Rainer Weikusat
<rweikusat@xxxxxxxxxxx> wrote in <87k5tsbfmj.fsf@xxxxxxxxxxxxxxxxx>:

Jan Panteltje <pNaonStpealmtje@xxxxxxxxx> writes:

[...]


/* test if file is locked */
i = 0;
while(1)
{
a = lockf(fileno(lockfile), F_TEST, 0);
if(a != -1) break;

if(errno != EAGAIN)
{
fprintf(stderr, "MyProgram: An other MyProgram is already running, aborting.\n");

exit(1);
}

i++;
if(i == 1000) // 10 S
{
fprintf(stderr, "MyProgram: timeout EAGAIN waiting for lockf() F_TEST, aborting.\n");

exit(1);
}

usleep(10000); // 10 ms
}

This loop is totally useless, because by the time you do the second
lockf call, the file may or may not be locked and it doesn't matter
what another lockf call happening in the past returned.

EAGAIN means test again, and I have tested this soft and forced the EAGAIN condition.
Unless (we still have to look at the lockf() source) EAGAIN is used wrongly, the loop is correct.

I have see errno values been used wrongly before.
It is just playing safe.


.

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