Re: glibc can call alarm() | wass Re: [CRASH] with socks

Andreas Jaeger <aj(a)suse.de&gt; writes: This is typical usage, i.e. old_timeout = alarm(0); push new SIGALARM handler alarm(our_time); /* do your thing */ alarm(0); pop SIGALARM handler alarm(old_timeout); The reason XEmacs overrides the alarm() functions is exactly to detect stuff like this because it is often wrong urysohn:/tmp> gcc testlarm.c [1] urysohn:/tmp> ./a.out value from alarm() was : 1 Restored to: 1.000000 s , should be 0.000500 s Repeat to: 0.000000 s , should be 0.000700 s So IMO this is a bug in glibc (should I file one?) 1. This really is a wart in the Unix API. The above code is only correct if our_time << old_timeout (because it doesn't check for the fact that the real timer could very well have expired. For that reason it would be really nice if glibc would refrain from messing with the timers, especially in stuff like get_login() where it is not obvious. 2. If it really wants to mess with the timer (Don't the posix realtime extensions now offer independent timers?), it should do so using getitimer/setitimer because that doesn't loose precision and repeat values. Jan Footnotes: [1] #include <stdio.h> #include <sys/time.h> #include <time.h> int main (int argc, char *argv[]) { struct itimerval mydelay = {{0, 700} , {0,500}}; /* 500 msec, repeat 700 */ struct itimerval newdelay; int inseconds; if (setitimer(ITIMER_REAL,&mydelay,NULL)) { perror("setimer: "); exit(1); } inseconds = alarm(0); alarm(inseconds); getitimer(ITIMER_REAL,&newdelay); alarm(0); printf("value from alarm() was : %i\n",inseconds); printf("Restored to: %li.%6.6li s , should be %li.%6.6li s\n", newdelay.it_value.tv_sec, newdelay.it_value.tv_usec, mydelay.it_value.tv_sec, mydelay.it_value.tv_usec); printf("Repeat to: %li.%6.6li s , should be %li.%6.6li s\n", newdelay.it_interval.tv_sec, newdelay.it_interval.tv_usec, mydelay.it_interval.tv_sec, mydelay.it_interval.tv_usec); } -- Jan Vroonhof http://www.math.ethz.ch/~vroonhof/ Mathematik, vroonhof ＠ math.ethz.ch HG E16, ETH-Zentrum, Tel: +41-1-6325456/25154 Raemistrasse 101, CH-8092 Zuerich. Fax: +41-1-6321085