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libbeat: Stop autodiscover runners in a goroutine #7170

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merged 1 commit into from
May 28, 2018

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Stopping runners can be a blocking operation, what can block the
autodiscover event loop. Run it in a goroutine so events can continue
being handled.

@jsoriano jsoriano added discuss Issue needs further discussion. libbeat labels May 24, 2018
@jsoriano jsoriano requested review from urso and exekias May 24, 2018 11:18
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LGTM, it will need a changelog, as I think this is a bugfix

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exekias commented May 24, 2018

@urso @ruflin I find this interesting, do you have any insight about why module stopping may block for a while?

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exekias commented May 24, 2018

@jsoriano we should backport this to, at least, 6.3

@jsoriano jsoriano added needs_backport PR is waiting to be backported to other branches. bug labels May 24, 2018
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jsoriano commented May 24, 2018

In case it gives any clue, runner.Start() doesn't seem to block, and when it is blocked on Stop() it also blocks graceful stop of the process with Ctrl-C.

@@ -178,7 +178,7 @@ func (a *Autodiscover) handleStop(event bus.Event) {

if runner := a.runners.Get(hash); runner != nil {
logp.Info("Autodiscover stopping runner: %s", runner)
runner.Stop()
go runner.Stop()
a.runners.Remove(hash)
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the hash should only be removed if stopping is finished I would think

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We actually want to remove it here, if a new event arrives to start the same module we want that to happen, even if the previous instance is still stopping

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I see, so adding and removing is synchronous. To make it more clear in the code we should add a comment here and move the stopping command after the removal of the hash.

Any concerns about leaking go routines here if Stop() gets stuck?

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ruflin commented May 24, 2018

Could this cause some race conditions?

@exekias exekias added the v6.3.0 label May 24, 2018
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@ruflin it is possible, yes, not sure what happens if a runner is stopped twice.

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exekias commented May 25, 2018

I don't think it's possible, events are processed by autodiscover one bye one, it acts as a state machine. This should ensure that the event is removed from the list by the moment you process the next event. For instance 2 stop events (this can happen) would go like this:

  • First event calls runner.Stop() as a goroutine, stop beggins. The runner is removed from the list.
  • Second event goes to the list and see no runner for the given config, so it does nothing; even if the runner is still stopping.

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Added changelog.

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ruflin commented May 25, 2018

Change LGTM but I think we should document what we discussed here in the code for the next person touching this code.

Stopping runners can be a blocking operation, what can block the
autodiscover event loop. Run it in a goroutine so events can continue
being handled.
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@ruflin ok, I have added a comment explaining the decissions there.

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ruflin commented May 28, 2018

jenkins, test this

@ruflin ruflin merged commit 500ab7c into elastic:master May 28, 2018
@jsoriano jsoriano added v6.3.0 and removed needs_backport PR is waiting to be backported to other branches. labels May 28, 2018
jsoriano added a commit to jsoriano/beats that referenced this pull request May 28, 2018
Stopping runners can be a blocking operation, what can block the
autodiscover event loop. Run it in a goroutine so events can continue
being handled.

(cherry picked from commit 500ab7c)
exekias pushed a commit that referenced this pull request May 29, 2018
Stopping runners can be a blocking operation, what can block the
autodiscover event loop. Run it in a goroutine so events can continue
being handled.

(cherry picked from commit 500ab7c)
leweafan pushed a commit to leweafan/beats that referenced this pull request Apr 28, 2023
…stic#7186)

Stopping runners can be a blocking operation, what can block the
autodiscover event loop. Run it in a goroutine so events can continue
being handled.

(cherry picked from commit eb58c3a)
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3 participants