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The order of booting up a server should be Job scheduler -> Cluster. And shutdown should be the opposite. This is needed because the job scheduler initializes certain data structures that are later called by ClusterLeaderChanged event handlers. And the event handlers run in a separate goroutine. Therefore, if the cluster initialization happens before the job scheduler, then a race happens between accessing the jobs variable and setting it. To prevent this race, we fix the order of startup, and add comments in both places to prevent things from regressing again.
37 lines
1.3 KiB
Go
37 lines
1.3 KiB
Go
// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
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// See LICENSE.txt for license information.
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package app
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import (
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"github.com/mattermost/mattermost-server/v5/model"
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)
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// Registers a given function to be called when the cluster leader may have changed. Returns a unique ID for the
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// listener which can later be used to remove it. If clustering is not enabled in this build, the callback will never
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// be called.
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func (s *Server) AddClusterLeaderChangedListener(listener func()) string {
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id := model.NewId()
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s.clusterLeaderListeners.Store(id, listener)
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return id
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}
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// Removes a listener function by the unique ID returned when AddConfigListener was called
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func (s *Server) RemoveClusterLeaderChangedListener(id string) {
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s.clusterLeaderListeners.Delete(id)
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}
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func (s *Server) InvokeClusterLeaderChangedListeners() {
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s.Log.Info("Cluster leader changed. Invoking ClusterLeaderChanged listeners.")
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// This needs to be run in a separate goroutine otherwise a recursive lock happens
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// because the listener function eventually ends up calling .IsLeader().
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// Fixing this would require the changed event to pass the leader directly, but that
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// requires a lot of work.
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s.Go(func() {
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s.clusterLeaderListeners.Range(func(_, listener interface{}) bool {
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listener.(func())()
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return true
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})
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})
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}
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