From a620147a23d06b7275c6bf4d91010a6d852c0262 Mon Sep 17 00:00:00 2001
From: Egon Elbre <egonelbre@gmail.com>
Date: Mon, 3 Oct 2022 18:37:41 +0300
Subject: [PATCH] avoid background goroutine

---
 client.go | 106 +++++++++++++++++++++++++-----------------------------
 1 file changed, 48 insertions(+), 58 deletions(-)

diff --git a/client.go b/client.go
index 42add0a..37b7b5b 100644
--- a/client.go
+++ b/client.go
@@ -3,16 +3,13 @@ package eventkit
 import (
 	"bytes"
 	"compress/zlib"
-	"context"
 	"net"
 	"sync"
 	"time"
 
 	"github.com/gogo/protobuf/proto"
-	"golang.org/x/sync/errgroup"
 
 	"github.com/jtolio/eventkit/pb"
-	"github.com/jtolio/eventkit/utils"
 )
 
 const (
@@ -37,8 +34,11 @@ type UDPClient struct {
 	CompressionLevel     int
 	FlushInterval        time.Duration
 
-	initOnce    sync.Once
-	submitQueue chan *Event
+	mu      sync.Mutex
+	closed  bool
+	active  sync.WaitGroup
+	pending *outgoingPacket
+	flush   chan struct{}
 }
 
 func NewUDPClient(application, version, instance, addr string) *UDPClient {
@@ -56,12 +56,6 @@ func NewUDPClient(application, version, instance, addr string) *UDPClient {
 	return c
 }
 
-func (c *UDPClient) init() {
-	c.initOnce.Do(func() {
-		c.submitQueue = make(chan *Event, c.QueueDepth)
-	})
-}
-
 type outgoingPacket struct {
 	buf                      bytes.Buffer
 	zl                       *zlib.Writer
@@ -153,47 +147,52 @@ func (op *outgoingPacket) addEvent(ev *Event) (full bool) {
 	return (op.written + trailerSize) > op.maxUncompressed
 }
 
-func (c *UDPClient) Run(ctx context.Context) {
-	c.init()
+func (c *UDPClient) Submit(event *Event) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 
-	ticker := utils.NewJitteredTicker(c.FlushInterval)
-	var background errgroup.Group
-	defer func() { _ = background.Wait() }()
-	background.Go(func() error {
-		ticker.Run(ctx)
-		return nil
-	})
+	if c.closed {
+		return
+	}
 
-	p := c.newOutgoingPacket()
-
-	sendAndReset := func() {
-		_ = c.send(p, c.Addr)
-		p = c.newOutgoingPacket()
-	}
-
-	for {
-		select {
-		case em := <-c.submitQueue:
-			if p.addEvent(em) {
-				sendAndReset()
-			}
-		case <-ticker.C:
-			if p.events > 0 {
-				sendAndReset()
-			}
-		case <-ctx.Done():
-			left := len(c.submitQueue)
-			for i := 0; i < left; i++ {
-				if p.addEvent(<-c.submitQueue) {
-					sendAndReset()
-				}
-			}
-			if p.events > 0 {
-				_ = c.send(p, c.Addr)
-			}
-			return
-		}
+	if c.pending == nil {
+		c.pending = c.newOutgoingPacket()
+		c.flush = make(chan struct{}, 1)
+		c.active.Add(1)
+		go c.waitForFull(c.pending, c.flush)
+	}
+
+	if c.pending.addEvent(event) {
+		c.flush <- struct{}{}
+		c.pending, c.flush = nil, nil
+	}
+}
+
+func (c *UDPClient) Close() {
+	c.mu.Lock()
+	c.closed = true
+	c.mu.Unlock()
+
+	c.active.Wait()
+}
+
+func (c *UDPClient) waitForFull(active *outgoingPacket, work chan struct{}) {
+	defer c.active.Done()
+
+	tick := time.NewTimer(c.FlushInterval) // TODO: jitter
+	select {
+	case <-work:
+	case <-tick.C:
 	}
+	tick.Stop()
+
+	c.mu.Lock()
+	if c.pending == active {
+		c.pending = nil
+	}
+	c.mu.Unlock()
+
+	c.send(active, c.Addr)
 }
 
 func (c *UDPClient) send(packet *outgoingPacket, addr string) (err error) {
@@ -215,12 +214,3 @@ func (c *UDPClient) send(packet *outgoingPacket, addr string) (err error) {
 	_, _, err = conn.WriteMsgUDP(packet.finalize(), nil, nil)
 	return err
 }
-
-func (c *UDPClient) Submit(event *Event) {
-	c.init()
-
-	select {
-	case c.submitQueue <- event:
-	default:
-	}
-}