Stop plugin healthchecks before shutting down plugins (#11972)

* cancel plugin check when shutdown

* move to top

* stop healthcheck job only once, and if started

* whitespace

plugin/environment.go

@@ -284,6 +284,10 @@ func (env *Environment) RestartPlugin(id string) error {
 
 // Shutdown deactivates all plugins and gracefully shuts down the environment.
 func (env *Environment) Shutdown() {
+	if env.pluginHealthCheckJob != nil {
+		env.pluginHealthCheckJob.Cancel()
+	}
+
 	env.registeredPlugins.Range(func(key, value interface{}) bool {
 		rp := value.(*registeredPlugin)
 

plugin/health_check.go

@@ -5,6 +5,7 @@ package plugin
 
 import (
 	"fmt"
+	"sync"
 	"time"
 
 	"github.com/mattermost/mattermost-server/mlog"
@@ -19,9 +20,10 @@ const (
 )
 
 type PluginHealthCheckJob struct {
-	cancel    chan struct{}
-	cancelled chan struct{}
-	env       *Environment
+	cancel     chan struct{}
+	cancelled  chan struct{}
+	cancelOnce sync.Once
+	env        *Environment
 }
 
 // InitPluginHealthCheckJob starts a new job if one is not running and is set to enabled, or kills an existing one if set to disabled.
@@ -125,7 +127,9 @@ func newPluginHealthCheckJob(env *Environment) *PluginHealthCheckJob {
 }
 
 func (job *PluginHealthCheckJob) Cancel() {
-	close(job.cancel)
+	job.cancelOnce.Do(func() {
+		close(job.cancel)
+	})
 	<-job.cancelled
 }