[FSSDK-8501] fix: gracefully close client to dispatch queued events (#376)

* wait for dispatching events on close

* update tests

* use context

* add unit test

* update tests

* refactor code

* refactor code

* fix linter

* update test

* update license header

Author: pulak-opti

pkg/event/dispatcher.go

@@ -1,5 +1,5 @@
 /****************************************************************************
- * Copyright 2019, Optimizely, Inc. and contributors                        *
+ * Copyright 2019,2023 Optimizely, Inc. and contributors                    *
  *                                                                          *
  * Licensed under the Apache License, Version 2.0 (the "License");          *
  * you may not use this file except in compliance with the License.         *
@@ -18,6 +18,7 @@
 package event
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"time"
@@ -100,9 +101,26 @@ func (ed *QueueEventDispatcher) DispatchEvent(event LogEvent) (bool, error) {
 	return true, nil
 }
 
+// waitForDispatchingEventsOnClose will wait until all the event are dispatched
+func (ed *QueueEventDispatcher) waitForDispatchingEventsOnClose(timeout time.Duration) {
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		default:
+			if ed.eventQueue.Size() == 0 {
+				return
+			}
+			time.Sleep(CloseEventDispatchWaitTime)
+		}
+	}
+}
+
 // flush the events
 func (ed *QueueEventDispatcher) flushEvents() {
-
 	// Limit flushing to a single worker
 	if !ed.processing.TryAcquire(1) {
 		return

pkg/event/dispatcher_test.go

@@ -1,5 +1,5 @@
 /****************************************************************************
- * Copyright 2019-2020,2022 Optimizely, Inc. and contributors               *
+ * Copyright 2019-2020,2022-2023 Optimizely, Inc. and contributors          *
  *                                                                          *
  * Licensed under the Apache License, Version 2.0 (the "License");          *
  * you may not use this file except in compliance with the License.         *
@@ -197,3 +197,40 @@ func TestQueueEventDispatcher_FailDispath(t *testing.T) {
 	assert.Equal(t, float64(1), metricsRegistry.GetGauge(metrics.DispatcherQueueSize).(*MetricsGauge).Get())
 	assert.Equal(t, float64(0), metricsRegistry.GetCounter(metrics.DispatcherSuccessFlush).(*MetricsCounter).Get())
 }
+
+func TestQueueEventDispatcher_WaitForDispatchingEventsOnClose(t *testing.T) {
+	metricsRegistry := NewMetricsRegistry()
+
+	q := NewQueueEventDispatcher("", metricsRegistry)
+
+	assert.True(t, q.Dispatcher != nil)
+	if d, ok := q.Dispatcher.(*httpEventDispatcher); ok {
+		assert.True(t, d.requester != nil && d.logger != nil)
+	} else {
+		assert.True(t, false)
+	}
+	sender := &MockDispatcher{Events: NewInMemoryQueue(100), eventsQueue: NewInMemoryQueue(100)}
+	q.Dispatcher = sender
+
+	eventTags := map[string]interface{}{"revenue": 55.0, "value": 25.1}
+	config := TestConfig{}
+
+	for i := 0; i < 10; i++ {
+		conversionUserEvent := CreateConversionUserEvent(config, entities.Event{ExperimentIds: []string{"15402980349"}, ID: "15368860886", Key: "sample_conversion"}, userContext, eventTags)
+
+		batch := createBatchEvent(conversionUserEvent, createVisitorFromUserEvent(conversionUserEvent))
+		assert.Equal(t, conversionUserEvent.Timestamp, batch.Visitors[0].Snapshots[0].Events[0].Timestamp)
+
+		logEvent := createLogEvent(batch, DefaultEventEndPoint)
+
+		success, _ := q.DispatchEvent(logEvent)
+
+		assert.True(t, success)
+	}
+
+	// wait for the events to be dispatched
+	q.waitForDispatchingEventsOnClose(10 * time.Second)
+
+	// check the queue
+	assert.Equal(t, 0, q.eventQueue.Size())
+}

pkg/event/processor.go

@@ -65,6 +65,12 @@ const DefaultEventQueueSize = 2000
 // DefaultEventFlushInterval holds the default value for the event flush interval
 const DefaultEventFlushInterval = 30 * time.Second
 
+// CloseEventDispatchWaitTime holds the checking interval for the dispatching events on client close
+const CloseEventDispatchWaitTime = 500 * time.Millisecond
+
+// CloseEventDispatchTimeout holds the timeout value for the waiting for the dispatching events on client close
+const CloseEventDispatchTimeout = 30 * time.Second
+
 // DefaultEventEndPoint is used as the default endpoint for sending events.
 const DefaultEventEndPoint = "https://logx.optimizely.com/v1/events"
 
@@ -245,6 +251,7 @@ func (p *BatchEventProcessor) startTicker(ctx context.Context) {
 			d, ok := p.EventDispatcher.(*QueueEventDispatcher)
 			if ok {
 				d.flushEvents()
+				d.waitForDispatchingEventsOnClose(CloseEventDispatchTimeout)
 			}
 			p.Ticker.Stop()
 			return

pkg/event/processor_test.go

@@ -1,5 +1,5 @@
 /****************************************************************************
- * Copyright 2019-2020, Optimizely, Inc. and contributors                   *
+ * Copyright 2019-2020,2023 Optimizely, Inc. and contributors               *
  *                                                                          *
  * Licensed under the Apache License, Version 2.0 (the "License");          *
  * you may not use this file except in compliance with the License.         *
@@ -43,8 +43,9 @@ func (c *CountingDispatcher) DispatchEvent(event LogEvent) (bool, error) {
 }
 
 type MockDispatcher struct {
-	ShouldFail bool
-	Events     Queue
+	ShouldFail  bool
+	Events      Queue
+	eventsQueue Queue // dispatch events from this queue
 }
 
 func (m *MockDispatcher) DispatchEvent(event LogEvent) (bool, error) {
@@ -53,11 +54,22 @@ func (m *MockDispatcher) DispatchEvent(event LogEvent) (bool, error) {
 	}
 
 	m.Events.Add(event)
+	if m.eventsQueue != nil {
+		m.eventsQueue.Add(event)
+		go m.flushEvents()
+	}
 	return true, nil
 }
 
+func (m *MockDispatcher) flushEvents() {
+	queueSize := m.eventsQueue.Size()
+	for ; queueSize > 0; queueSize = m.eventsQueue.Size() {
+		m.eventsQueue.Remove(1)
+	}
+}
+
 func NewMockDispatcher(queueSize int, shouldFail bool) *MockDispatcher {
-	return &MockDispatcher{Events: NewInMemoryQueue(queueSize), ShouldFail: shouldFail}
+	return &MockDispatcher{Events: NewInMemoryQueue(queueSize), eventsQueue: NewInMemoryQueue(queueSize), ShouldFail: shouldFail}
 }
 
 func newExecutionContext() *utils.ExecGroup {
@@ -180,7 +192,6 @@ func TestDefaultEventProcessor_BatchSizes(t *testing.T) {
 		assert.Equal(t, 50, len(logEvent.Event.Visitors))
 		logEvent, _ = evs[1].(LogEvent)
 		assert.Equal(t, 50, len(logEvent.Event.Visitors))
-
 	}
 	eg.TerminateAndWait()
 }
@@ -493,7 +504,7 @@ func (l *NoOpLogger) SetLogLevel(level logging.LogLevel) {
 
 }
 
-/**
+/*
 goos: darwin
 goarch: amd64
 pkg: github.com/optimizely/go-sdk/pkg/event