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

On a sunny day (Sun, 24 Jun 2007 17:48:50 +0200) it happened Michal Nazarewicz
<mina86@xxxxxxx> wrote in <87645dl5el.fsf@xxxxxxxxxxxxxxxx>:

I don't think you need two loops. From what I understood EAGAIN means
that file is already locked (or otherwise cannot be locked):

This is actually better, as while(1) had no timeout, now it has.

int a, i;
char temp[WHAT_SHALL_WE USE];
struct passwd *userinfo;
FILE *lockfile;

/* get user info */
userinfo = getpwuid(getuid() );

/* create a lockfile if it did not exist */
sprintf(temp, "%s/.MyProgram/lockfile", userinfo -> pw_dir);
lockfile = fopen(temp, "w");
if(! lockfile)
{
fprintf(stderr, "MyProgram: could not create lockfile %s aborting.\n", temp);

exit(1);
}

/* 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
}

/* lock the file */
i = 0;
while(1)
{
a = lockf(fileno(lockfile), F_TLOCK, 0);
if(a != -1) break;

if(errno != EAGAIN)
{
perror(" MyProgram: could not lock lockfile because: ");

exit(1);
}

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

exit(1);
}

usleep(10000); // 10 ms
}

/* file stays open, else lock is lost */

.

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