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Ensure task reaper stopChan is closed no more than once #2491

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Feb 1, 2018
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Ensure task reaper stopChan is closed no more than once #2491

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15 changes: 12 additions & 3 deletions manager/orchestrator/taskreaper/task_reaper.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ package taskreaper

import (
"sort"
"sync"
"time"

"github.com/docker/swarmkit/api"
Expand All @@ -24,6 +25,9 @@ const (
type TaskReaper struct {
store *store.MemoryStore

// closeOnce ensures that stopChan is closed only once
closeOnce sync.Once

// taskHistory is the number of tasks to keep
taskHistory int64

Expand Down Expand Up @@ -281,9 +285,14 @@ func (tr *TaskReaper) tick() {
}

// Stop stops the TaskReaper and waits for the main loop to exit.
// Stop can be called in two cases. One when the manager is
// shutting down, and the other when the manager (the leader) is
// becoming a follower. Since these two instances could race with
// each other, we use closeOnce here to ensure that TaskReaper.Stop()
// is called only once to avoid a panic.
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@anshulpundir added a comment here.

func (tr *TaskReaper) Stop() {
// TODO(dperny) calling stop on the task reaper twice will cause a panic
// because we try to close a channel that will already have been closed.
close(tr.stopChan)
tr.closeOnce.Do(func() {
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What is the reason to have multiple invocation for this function ?

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Kicked off a rebuild. Lets close this out soon ? @nishanttotla

close(tr.stopChan)
})
<-tr.doneChan
}