Disarm timer in runguard after child has exited. #2157
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If we would not disarm the timer, there is a possibility that the timer
sends us a SIGALRM while we are still busy with cleaning the sandbox up.
What you observe in these cases is a judging with wall time well below
the time limit is judged as TLE, e.g.
```
Timelimit exceeded.
runtime: 0.288s cpu, 0.302s wall
memory used: 26066944 bytes
********** runguard stderr follows **********
/opt/domjudge/bin/runguard: warning: timelimit exceeded (hard wall time): aborting command
```
In practice, we saw the behavior happening when running many
judgedaemons and domserver on a single machine while rejudging the whole
contest (i.e. under quite high load). In that case, the call
`cgroup_delete_cgroup_ext` did sometimes hang for multiple seconds.
For easy reproducibility, you can also add an artificial delay in the
clean up code, e.g. by adding something like:
```
const struct timespec artificial_delay = { 10, 0 };
nanosleep(&artificial_delay, NULL);
```
edomora97
approved these changes
Sep 27, 2023
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If we would not disarm the timer, there is a possibility that the timer sends us a SIGALRM while we are still busy with cleaning the sandbox up.
What you observe in these cases is a judging with wall time well below the time limit is judged as TLE, e.g.
In practice, we saw the behavior happening when running many judgedaemons and domserver on a single machine while rejudging the whole contest (i.e. under quite high load). In that case, the call
cgroup_delete_cgroup_extdid sometimes hang for multiple seconds.For easy reproducibility, you can also add an artificial delay in the clean up code, e.g. by adding something like: