config: move onChange callback list methods into a thread-safe wrapper

Signed-off-by: Benedikt Bongartz <bongartz@klimlive.de>

internal/config/change_handler.go

@@ -0,0 +1,64 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package config contains the operator's runtime configuration.
+package config
+
+import (
+	"sync"
+
+	"github.com/go-logr/logr"
+	logf "sigs.k8s.io/controller-runtime/pkg/log"
+)
+
+// ChangeHandler is implemented by any structure that is able to register callbacks
+// and call them using one single method.
+type ChangeHandler interface {
+	// Change will call every registered callback.
+	Change() error
+	// Register the given function as a callback that will be executed on Change
+	// is called.
+	Register(f func() error)
+}
+
+// NewOnChange returns thread-safe ChangeHandler.
+func NewOnChange() ChangeHandler {
+	return &onChange{
+		logger: logf.Log.WithName("change-handler"),
+	}
+}
+
+type onChange struct {
+	logger logr.Logger
+
+	callbacks   []func() error
+	muCallbacks sync.Mutex
+}
+
+func (o *onChange) Change() error {
+	o.muCallbacks.Lock()
+	defer o.muCallbacks.Unlock()
+	for _, fn := range o.callbacks {
+		if err := fn(); err != nil {
+			o.logger.Error(err, "change callback failed")
+		}
+	}
+	return nil
+}
+
+func (o *onChange) Register(f func() error) {
+	o.muCallbacks.Lock()
+	defer o.muCallbacks.Unlock()
+	o.callbacks = append(o.callbacks, f)
+}

internal/config/change_handler_test.go

@@ -0,0 +1,42 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package config contains the operator's runtime configuration.
+package config_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/open-telemetry/opentelemetry-operator/internal/config"
+)
+
+func TestChangeHandler(t *testing.T) {
+	// prepare
+	internal := 0
+	callback := func() error {
+		internal += 1
+		return nil
+	}
+	h := config.NewOnChange()
+
+	h.Register(callback)
+
+	for i := 0; i < 5; i++ {
+		require.NoError(t, h.Change())
+		assert.Equal(t, i, internal)
+	}
+}

internal/config/main.go

@@ -44,7 +44,7 @@ type Config struct {
 	targetAllocatorConfigMapEntry  string
 	autoInstrumentationNodeJSImage string
 	autoInstrumentationJavaImage   string
-	onChange                       []func() error
+	onChange                       ChangeHandler
 	labelsFilter                   []string
 	platform                       platform.Platform
 	autoDetectFrequency            time.Duration
@@ -125,12 +125,10 @@ func (c *Config) AutoDetect() error {
 	}
 
 	if changed {
-		for _, callback := range c.onChange {
-			if err := callback(); err != nil {
-				// we don't fail if the callback failed, as the auto-detection itself
-				// did work
-				c.logger.Error(err, "configuration change notification failed for callback")
-			}
+		if err := c.onChange.Change(); err != nil {
+			// we don't fail if the callback failed, as the auto-detection itself
+			// did work
+			c.logger.Error(err, "configuration change notification failed for callback")
 		}
 	}
 
@@ -198,3 +196,8 @@ func (c *Config) AutoInstrumentationDotNetImage() string {
 func (c *Config) LabelsFilter() []string {
 	return c.labelsFilter
 }
+
+// ChangeHandler the internal used ChangeHandler.
+func (c *Config) ChangeHandler() ChangeHandler {
+	return c.onChange
+}

internal/config/options.go

@@ -41,7 +41,7 @@ type options struct {
 	collectorConfigMapEntry        string
 	targetAllocatorConfigMapEntry  string
 	targetAllocatorImage           string
-	onChange                       []func() error
+	onChange                       ChangeHandler
 	labelsFilter                   []string
 	platform                       platform.Platform
 	autoDetectFrequency            time.Duration
@@ -84,12 +84,17 @@ func WithLogger(logger logr.Logger) Option {
 		o.logger = logger
 	}
 }
+func WithOnChangeHandler(h ChangeHandler) Option {
+	return func(o *options) {
+		o.onChange = h
+	}
+}
 func WithOnChange(f func() error) Option {
 	return func(o *options) {
 		if o.onChange == nil {
-			o.onChange = []func() error{}
+			o.onChange = NewOnChange()
 		}
-		o.onChange = append(o.onChange, f)
+		o.onChange.Register(f)
 	}
 }
 func WithPlatform(plt platform.Platform) Option {