[fix][prometheusexporter] Race condition between start and shutdown

.chloggen/fix_prometheusexporter-shutdown-server-2.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Fixes a race condition between the exporter start and shutdown functions."
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36139]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

exporter/prometheusexporter/prometheus.go

@@ -66,16 +66,12 @@ func (pe *prometheusExporter) Start(ctx context.Context, host component.Host) er
 	mux := http.NewServeMux()
 	mux.Handle("/metrics", pe.handler)
 	srv, err := pe.config.ToServer(ctx, host, pe.settings, mux)
-	pe.shutdownFunc = func(ctx context.Context) error {
-		errLn := ln.Close()
-		if srv == nil {
-			return errLn
-		}
-		errSrv := srv.Shutdown(ctx)
-		return errors.Join(errLn, errSrv)
-	}
 	if err != nil {
-		return err
+		lnerr := ln.Close()
+		return errors.Join(err, lnerr)
+	}
+	pe.shutdownFunc = func(ctx context.Context) error {
+		return srv.Shutdown(ctx)
 	}
 	go func() {
 		_ = srv.Serve(ln)