Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/channels/app/platform/goroutines.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package platform
+
+import "sync/atomic"
+
+// Go creates a goroutine, but maintains a record of it to ensure that execution completes before
+// the server is shutdown.
+func (ps *PlatformService) Go(f func()) {
+	atomic.AddInt32(&ps.goroutineCount, 1)
+
+	go func() {
+		f()
+
+		atomic.AddInt32(&ps.goroutineCount, -1)
+		select {
+		case ps.goroutineExitSignal <- struct{}{}:
+		default:
+		}
+	}()
+}
+
+// waitForGoroutines blocks until all goroutines created by PlatformService.Go() exit.
+func (ps *PlatformService) waitForGoroutines() {
+	for atomic.LoadInt32(&ps.goroutineCount) != 0 {
+		<-ps.goroutineExitSignal
+	}
+}
+
+func (ps *PlatformService) GoBuffered(f func()) {
+	ps.goroutineBuffered <- struct{}{}
+
+	atomic.AddInt32(&ps.goroutineCount, 1)
+
+	go func() {
+		f()
+
+		atomic.AddInt32(&ps.goroutineCount, -1)
+		select {
+		case ps.goroutineExitSignal <- struct{}{}:
+		default:
+		}
+
+		<-ps.goroutineBuffered
+	}()
+}