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From "Bernd Mathiske (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MESOS-1199) Subprocess is "slow" -> gated by process::reap poll interval
Date Mon, 28 Jul 2014 23:19:39 GMT

    [ https://issues.apache.org/jira/browse/MESOS-1199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14077114#comment-14077114
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Bernd Mathiske commented on MESOS-1199:
---------------------------------------

Idea: 

1. Iterate over the pids of interest, calling kill(pid, 0) on each pid. This returns immediately
and reports if the process is alive. 
2. Wait for a small timeout (100ms?)
3. Repeat.

This way, the wait time is a small constant plus n times the overhead of kill().

> 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
>            Assignee: Craig Hansen-Sturm
>
> 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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