fix: loki.source.file drain tasks on exit (#4593)

* Drain on exit

Author: kalleep

CHANGELOG.md

@@ -53,6 +53,8 @@ Main (unreleased)
 
 - Fix an issue where component shutdown could block indefinitely by adding a warning log message and a deadline of 10 minutes. The deadline can be configured with the `--feature.component-shutdown-deadline` flag if the default is not suitable. (@thampiotr)
 
+- Fix potential deadlocks in `loki.source.file` and `loki.source.journal` when component is shutting down. (@kalleep, @thampiotr)
+
 v1.11.1
 -----------------
 

internal/component/loki/source/file/file.go

@@ -145,6 +145,20 @@ func (c *Component) Run(ctx context.Context) error {
 	})
 	defer func() {
 		level.Info(c.opts.Logger).Log("msg", "loki.source.file component shutting down, stopping readers and positions file")
+
+		// Start black hole drain routine to prevent deadlock when we call c.t.Stop().
+		drainCtx, cancelDrain := context.WithCancel(context.Background())
+		defer cancelDrain()
+		go func() {
+			for {
+				select {
+				case <-drainCtx.Done():
+					return
+				case <-c.handler.Chan(): // Ignore the remaining entries
+				}
+			}
+		}()
+
 		c.tasksMut.RLock()
 		c.stopping.Store(true)
 		runner.Stop()