Bug#594742: libc6: clock_gettime(CLOCK_MONOTONIC) not monotonic
Package: libc6
Version: 2.11.2-2
Severity: normal
This program:
#include <time.h>
#include <assert.h>
#include <stdio.h>
int main()
{
struct timespec last_time, current_time;
int r;
clockid_t id;
assert(clock_gettime(CLOCK_MONOTONIC, &last_time) == 0);
r = clock_getcpuclockid(0, &id);
printf("r: %d, id: %d\n", r, id);
while (1) {
assert(clock_gettime(CLOCK_MONOTONIC, ¤t_time) == 0);
assert(current_time.tv_sec >= last_time.tv_sec);
assert((current_time.tv_sec > last_time.tv_sec) ||
(current_time.tv_nsec >= last_time.tv_nsec));
last_time = current_time;
}
}
when run:
$ gcc -std=gnu99 -lrt monotonic2.c && ./a.out
r: 0, id: -6
a.out: monotonic2.c:16: main: Assertion `(current_time.tv_sec > last_time.tv_sec) || (current_time.tv_nsec >= last_time.tv_nsec)' failed.
Shouldn't trigger an assert... The function guarantees monotonic time
increments, but apparently that promise is broken here. I am running
this on an SMP system, but the output of clock_getcpuclockid(0) is not
ENOENT, so it should really be monotonic...
The CPU is an Intel Q9450.
Credits of test program: Wouter Vermaelen.
-- System Information:
Debian Release: squeeze/sid
APT prefers testing
APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Kernel: Linux 2.6.32-5-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Versions of packages libc6 depends on:
ii libc-bin 2.11.2-2 Embedded GNU C Library: Binaries
ii libgcc1 1:4.4.4-8 GCC support library
libc6 recommends no packages.
Versions of packages libc6 suggests:
ii debconf [debconf-2.0] 1.5.35 Debian configuration management sy
pn glibc-doc <none> (no description available)
ii locales 2.11.2-2 Embedded GNU C Library: National L
-- debconf information:
* glibc/upgrade: true
glibc/disable-screensaver:
glibc/restart-failed:
* glibc/restart-services: gdm openbsd-inetd exim4 cups cron atd
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