events: close channel explicitly

[stevvooe]

Signed-off-by: Stephen J Day stephen.day@docker.com

[codecov-io]

Codecov Report

Merging #1254 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1254   +/-   ##
=======================================
  Coverage   28.02%   28.02%           
=======================================
  Files          29       29           
  Lines        3033     3033           
=======================================
  Hits          850      850           
  Misses       2033     2033           
  Partials      150      150

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[estesp]

At some point, with this patch applied to master, my debug containerd log starts to fill with:

DEBU[0129] eventqueue: dropped event                     error="events: sink closed" event=&Envelope{Timestamp:2017-07-27 21:39:24.675133705 +0000 UTC,Namespace:,Topic:/containers/delete,Event:&google_protobuf1.Any{TypeUrl:types.containerd.io/containerd.services.events.v1.ContainerDelete,Value:[10 11 98 98 45 99 116 114 45 48 45 50 49],},} sink=map[C:0xc420bd7f20 closed:0xc420bd7f80]

After a few thousand lines of that, I end up back in a hung state :(

[stevvooe]

@estesp Is the client hanging or containerd?

[estesp]

Just for posterity for this PR discussion thread (given we discussed on Slack): it is the client hanging because gRPC APIs on the server-side are blocked on something. I can create new containers via a secondary client, so containerd itself is not truly hung. But, the client which created the containers is waiting on deletes/waits to complete/return from the gRPC API, so is effectively hung as the server-side goroutines handling those APIs are not returning.

This PR does change the goroutine trace on the server-side. There are no more goroutines stuck in semacquire in the Queue.Close() code, so seems this fix is valid no matter what.

[dmcgowan]

LGTM