I have encounted a bug in Cygwin whereby ualarm(0,0) is not clearing
previously set ualarms. This first cropped up while using Perl, but I
was able to reproduce the bug with the following 'C' program. The gist
is that ualarm() is used several times, and then a final ualarm(0,0) is
executed to clear them. This is followed by a usleep(). The alarm
signal handler shows that 'bogus' alarms are going off during the
usleep(). Without the signal handler, the program would terminate
prematurely due to uncaught SIGALRM.
/*
* Reproduces bug associated with ualarm
*
* Make using: gcc -o ualarm_bug.exe ualarm_bug.c
*
* Typical output:
*
* First ualarm - one shot
* Second ualarm - one shot
* Last ualarm - repeats 3 times
* Clearing ualarm
* Sleeping
* --- BOGUS ALARM ---
* --- BOGUS ALARM ---
* Done
*
*/
#include <unistd.h>
#include <signal.h>
/* Increments a counter when alarm goes off */
int tick;
void
inc_tick(int signal)
{
tick++;
}
/* Prints out a warning message when an alarm goes off */
void
bogus(int signal)
{
printf("--- BOGUS ALARM ---\n");
}
int
main(int argc, char **argv)
{
int counter;
/* Set incrementing alarm handler */
signal(SIGALRM, &inc_tick);
printf("First ualarm - one shot\n");
tick = 0; ualarm(10000, 0); while (tick == 0) { counter++; };
printf("Second ualarm - one shot\n");
tick = 0; ualarm(10000, 0); while (tick == 0) { counter++; };
printf("Last ualarm - repeats 3 times\n");
tick = 0; ualarm(10000, 10000); while (tick < 3) { counter++; };
printf("Clearing ualarm\n");
ualarm(0, 0);
/* Set warning alarm handler */
signal(SIGALRM, &bogus);
printf("Sleeping\n");
usleep(500000);
printf("Done\n");
exit(0);
}
/* EOF */
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