BUG: ualarm(0,0) not clearing ualarms

Mon Feb 13 19:43:00 GMT 2006

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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