[processor/remotetap] Fix memory leak on shutdown (open-telemetry#32571)

The remotetap processor holds a map of channels for writing telemetry
data to WebSockets when a client connects. The write process works by
blocking on a given channel waiting for telemetry data coming through
the processor's pipeline, then writing as soon as it comes in. This
however can result in a leaked goroutine that blocks forever if data is
not received, which is always the case when shutting down.

This fixes the bug by closing and deleting all channels once all client
connections have been shutdown gracefully. This fixes the blocking
behavior during shutdown.

This change also enables `goleak` to help ensure no goroutines are being
leaked.

**Link to tracking Issue:** open-telemetry#30438

---------

Co-authored-by: Alex Boten <223565+codeboten@users.noreply.github.com>

.chloggen/goleak_remotetap.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: remotetapprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix memory leak on shutdown
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32571]
+
+# (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: []

processor/remotetapprocessor/channelset.go

@@ -48,3 +48,22 @@ func (c *channelSet) closeAndRemove(key int) {
 	delete(c.chanmap, key)
 	c.mu.Unlock()
 }
+
+func (c *channelSet) shutdown() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	// Get all keys before deletion, so the map is not
+	// being modified while iterating.
+	keys := make([]int, len(c.chanmap))
+	i := 0
+	for key := range c.chanmap {
+		keys[i] = key
+		i++
+	}
+
+	for key := range keys {
+		close(c.chanmap[key])
+		delete(c.chanmap, key)
+	}
+}

processor/remotetapprocessor/go.mod

@@ -14,6 +14,7 @@ require (
 	go.opentelemetry.io/collector/processor v0.99.0
 	go.opentelemetry.io/otel/metric v1.25.0
 	go.opentelemetry.io/otel/trace v1.25.0
+	go.uber.org/goleak v1.3.0
 	go.uber.org/zap v1.27.0
 	golang.org/x/net v0.24.0
 	golang.org/x/time v0.5.0

processor/remotetapprocessor/metadata.yaml

@@ -12,5 +12,3 @@ status:
 
 tests:
   config:
-  goleak:
-    skip: true

processor/remotetapprocessor/processor.go

@@ -81,11 +81,20 @@ func (w *wsprocessor) handleConn(conn *websocket.Conn) {
 }
 
 func (w *wsprocessor) Shutdown(ctx context.Context) error {
+	var err error
+
 	if w.server != nil {
-		err := w.server.Shutdown(ctx)
-		return err
+		err = w.server.Shutdown(ctx)
+		w.shutdownWG.Wait()
 	}
-	return nil
+
+	// The processor's channelset is only modified by its server, so once
+	// it's completely shutdown it's safe to shutdown the channelset itself.
+	if w.cs != nil {
+		w.cs.shutdown()
+	}
+
+	return err
 }
 
 func (w *wsprocessor) ConsumeMetrics(_ context.Context, md pmetric.Metrics) (pmetric.Metrics, error) {