Deregister pipeline loader callback when inputsRunner is stopped

CHANGELOG.asciidoc

@@ -37,6 +37,7 @@ https://github.com/elastic/beats/compare/v6.4.0...master[Check the HEAD diff]
 - Fix potential data loss on OS X in spool file by using fcntl with F_FULLFSYNC. {pull}7859[7859]
 - Improve fsync on linux, by assuming the kernel resets error flags of failed writes. {pull}7859[7859]
 - Remove unix-like permission checks on Windows, so files can be opened. {issue}7849[7849]
+- Deregister pipeline loader callback when inputsRunner is stopped. {pull}[7893][7893]
 
 *Auditbeat*
 

filebeat/fileset/factory.go

@@ -18,6 +18,8 @@
 package fileset
 
 import (
+	uuid "github.com/satori/go.uuid"
+
 	"github.com/elastic/beats/filebeat/channel"
 	input "github.com/elastic/beats/filebeat/prospector"
 	"github.com/elastic/beats/filebeat/registrar"
@@ -46,6 +48,7 @@ type Factory struct {
 	beatVersion           string
 	pipelineLoaderFactory PipelineLoaderFactory
 	overwritePipelines    bool
+	pipelineCallbackID    uuid.UUID
 	beatDone              chan struct{}
 }
 
@@ -55,6 +58,7 @@ type inputsRunner struct {
 	moduleRegistry        *ModuleRegistry
 	inputs                []*input.Runner
 	pipelineLoaderFactory PipelineLoaderFactory
+	pipelineCallbackID    uuid.UUID
 	overwritePipelines    bool
 }
 
@@ -67,6 +71,7 @@ func NewFactory(outlet channel.Factory, registrar *registrar.Registrar, beatVers
 		beatVersion:           beatVersion,
 		beatDone:              beatDone,
 		pipelineLoaderFactory: pipelineLoaderFactory,
+		pipelineCallbackID:    uuid.Nil,
 		overwritePipelines:    overwritePipelines,
 	}
 }
@@ -107,14 +112,20 @@ func (f *Factory) Create(p beat.Pipeline, c *common.Config, meta *common.MapStrP
 		moduleRegistry:        m,
 		inputs:                inputs,
 		pipelineLoaderFactory: f.pipelineLoaderFactory,
+		pipelineCallbackID:    f.pipelineCallbackID,
 		overwritePipelines:    f.overwritePipelines,
 	}, nil
 }
 
 func (p *inputsRunner) Start() {
 	// Load pipelines
 	if p.pipelineLoaderFactory != nil {
-		// Load pipelines instantly and then setup a callback for reconnections:
+		// Attempt to load pipelines instantly when starting or after reload.
+		// Thus, if ES was not available previously, it could be loaded this time.
+		// If the function below fails, it means that ES is not available
+		// at the moment, so the pipeline loader cannot be created.
+		// Registering a callback regardless of the availability of ES
+		// makes it possible to try to load pipeline when ES becomes reachable.
 		pipelineLoader, err := p.pipelineLoaderFactory()
 		if err != nil {
 			logp.Err("Error loading pipeline: %s", err)
@@ -126,11 +137,11 @@ func (p *inputsRunner) Start() {
 			}
 		}
 
-		// Callback:
+		// Register callback to try to load pipelines when connecting to ES.
 		callback := func(esClient *elasticsearch.Client) error {
 			return p.moduleRegistry.LoadPipelines(esClient, p.overwritePipelines)
 		}
-		elasticsearch.RegisterConnectCallback(callback)
+		p.pipelineCallbackID = elasticsearch.RegisterConnectCallback(callback)
 	}
 
 	for _, input := range p.inputs {
@@ -143,6 +154,10 @@ func (p *inputsRunner) Start() {
 	}
 }
 func (p *inputsRunner) Stop() {
+	if p.pipelineCallbackID != uuid.Nil {
+		elasticsearch.DeregisterConnectCallback(p.pipelineCallbackID)
+	}
+
 	for _, input := range p.inputs {
 		input.Stop()
 	}

libbeat/outputs/elasticsearch/elasticsearch.go

@@ -22,6 +22,8 @@ import (
 	"fmt"
 	"sync"
 
+	uuid "github.com/satori/go.uuid"
+
 	"github.com/elastic/beats/libbeat/beat"
 	"github.com/elastic/beats/libbeat/common"
 	"github.com/elastic/beats/libbeat/common/transport/tlscommon"
@@ -49,20 +51,48 @@ var (
 	ErrResponseRead = errors.New("bulk item status parse failed")
 )
 
+// Callbacks must not depend on the result of a previous one,
+// because the ordering is not fixed.
 type callbacksRegistry struct {
-	callbacks []connectCallback
+	callbacks map[uuid.UUID]connectCallback
 	mutex     sync.Mutex
 }
 
 // XXX: it would be fantastic to do this without a package global
-var connectCallbackRegistry callbacksRegistry
+var connectCallbackRegistry = newCallbacksRegistry()
+
+func newCallbacksRegistry() callbacksRegistry {
+	return callbacksRegistry{
+		callbacks: make(map[uuid.UUID]connectCallback),
+	}
+}
 
 // RegisterConnectCallback registers a callback for the elasticsearch output
 // The callback is called each time the client connects to elasticsearch.
-func RegisterConnectCallback(callback connectCallback) {
+// It returns the key of the newly added callback, so it can be deregistered later.
+func RegisterConnectCallback(callback connectCallback) uuid.UUID {
+	connectCallbackRegistry.mutex.Lock()
+	defer connectCallbackRegistry.mutex.Unlock()
+
+	// find the next unique key
+	var key uuid.UUID
+	exists := true
+	for exists {
+		key = uuid.NewV4()
+		_, exists = connectCallbackRegistry.callbacks[key]
+	}
+
+	connectCallbackRegistry.callbacks[key] = callback
+	return key
+}
+
+// DeregisterConnectCallback deregisters a callback for the elasticsearch output
+// specified by its key. If a callback does not exist, nothing happens.
+func DeregisterConnectCallback(key uuid.UUID) {
 	connectCallbackRegistry.mutex.Lock()
 	defer connectCallbackRegistry.mutex.Unlock()
-	connectCallbackRegistry.callbacks = append(connectCallbackRegistry.callbacks, callback)
+
+	delete(connectCallbackRegistry.callbacks, key)
 }
 
 func makeES(

libbeat/outputs/elasticsearch/elasticsearch_test.go

@@ -0,0 +1,39 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 elasticsearch
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestConnectCallbacksManagement(t *testing.T) {
+	f0 := func(client *Client) error { fmt.Println("i am function #0"); return nil }
+	f1 := func(client *Client) error { fmt.Println("i am function #1"); return nil }
+	f2 := func(client *Client) error { fmt.Println("i am function #2"); return nil }
+
+	_ = RegisterConnectCallback(f0)
+	id1 := RegisterConnectCallback(f1)
+	id2 := RegisterConnectCallback(f2)
+
+	t.Logf("removing second callback")
+	DeregisterConnectCallback(id1)
+	if _, ok := connectCallbackRegistry.callbacks[id2]; !ok {
+		t.Fatalf("third callback cannot be retrieved")
+	}
+}