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https://issues.apache.org/jira/browse/MESOS-1199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13963326#comment-13963326
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Benjamin Mahler commented on MESOS-1199:
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[~t.st.clair]:
{code}
// TODO(bmahler): This can be optimized to use a thread per pid, where
// each thread makes a blocking call to waitpid. This eliminates the
// unfortunate 1 second reap delay.
{code}
I didn't add this optimization as at that time we were mostly using reaping for
executors. These may actually be owned by 'init' since the slave process can
restart, in which case we cannot use waitpid. However, for Ian's new cases, it
makes a lot more sense and we may want to do this. We probably also want to
make sure we do this right, that is, ensure we don't use too many threads.
> Subprocess is "slow" -> gated by process::reap poll interval
> ------------------------------------------------------------
>
> Key: MESOS-1199
> URL: https://issues.apache.org/jira/browse/MESOS-1199
> Project: Mesos
> Issue Type: Improvement
> Affects Versions: 0.18.0
> Reporter: Ian Downes
>
> Subprocess uses process::reap to wait on the subprocess pid and set the exit
> status. However, process::reap polls with a one second interval resulting in
> a delay up to the interval duration before the status future is set.
> This means if you need to wait for the subprocess to complete you get hit
> with E(delay) = 0.5 seconds, independent of the execution time. For example,
> the MesosContainerizer uses mesos-fetcher in a Subprocess to fetch the
> executor during launch. At Twitter we fetch a local file, i.e., a very fast
> operation, but the launch is blocked until the mesos-fetcher pid is reaped ->
> adding 0 to 1 seconds for every launch!
> The problem is even worse with a chain of short Subprocesses because after
> the first Subprocess completes you'll be synchronized with the reap interval
> and you'll see nearly the full interval before notification, i.e., 10
> Subprocesses each of << 1 second duration with take ~10 seconds!
> This has become particularly apparent in some new tests I'm working on where
> test durations are now greatly extended with each taking several seconds.
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