use the old SetFinalizer instead of AddCleanup

Standard library functions of newer go versions can't be used without also bumping the go.mod go version, so switched PubSub to the old runtime.SetFinalizer() instead of the go1.24+ runtime.AddCleanup(), and added a test to make sure it works correctly.

Author: bitbullet

go.mod

@@ -1,11 +1,5 @@
 module github.com/koonix/go-livereload
 
-// Require 1.22+ to benefit from the for-loop changes.
-// https://tip.golang.org/doc/go1.22#language
 go 1.22
 
-// Use 1.24+ so we can use the runtime.AddCleanup function.
-// https://tip.golang.org/doc/go1.24#improved-finalizers
-toolchain go1.24.0
-
 require golang.org/x/net v0.35.0

internal/pubsub/pubsub.go

@@ -26,15 +26,23 @@ type sub[T any] struct {
 }
 
 func New[T any]() *PubSub[T] {
+
 p := &PubSub[T]{
 msg: make(chan T),
 addSub: make(chan *sub[T]),
 removeSub: make(chan *sub[T]),
 done: make(chan struct{}),
 }
-cleanup := runtime.AddCleanup(p, func(ch chan struct{}) { close(ch) }, p.done)
+runtime.SetFinalizer(p, func(p *PubSub[T]) {
+p.Close()
+})
+
+msg := p.msg
+addSub := p.addSub
+removeSub := p.removeSub
+done := p.done
+
 go func() {
-cleanup.Stop()
 subs := make(map[*sub[T]]struct{})
 defer func() {
 for sub := range subs {
@@ -43,14 +51,14 @@ func New[T any]() *PubSub[T] {
 }()
 for {
 select {
-case <-p.done:
+case <-done:
 return
-case sub := <-p.addSub:
+case sub := <-addSub:
 subs[sub] = struct{}{}
-case sub := <-p.removeSub:
+case sub := <-removeSub:
 delete(subs, sub)
 close(sub.msg)
-case msg := <-p.msg:
+case msg := <-msg:
 wg := new(sync.WaitGroup)
 wg.Add(len(subs))
 for sub := range subs {
@@ -66,18 +74,22 @@ func New[T any]() *PubSub[T] {
 }
 }
 }()
+
 return p
 }
 
 func (p *PubSub[T]) Subscribe() (msg <-chan T, unsubscribe func()) {
+
 sub := &sub[T]{
 msg: make(chan T, 1),
 done: make(chan struct{}),
 }
+
 select {
 case p.addSub <- sub:
 case <-p.done:
 }
+
 unsub := func() {
 sub.once.Do(func() {
 close(sub.done)
@@ -87,6 +99,7 @@ func (p *PubSub[T]) Subscribe() (msg <-chan T, unsubscribe func()) {
 }
 })
 }
+
 return sub.msg, unsub
 }
 

internal/pubsub/pubsub_test.go

@@ -1,20 +1,19 @@
 // Copyright 2024 the go-livereload authors.
 // SPDX-License-Identifier: Apache-2.0
 
-package pubsub_test
+package pubsub
 
 import (
-"fmt"
+"runtime"
 "sync"
 "sync/atomic"
 "testing"
-
-"github.com/koonix/go-livereload/internal/pubsub"
+"time"
 )
 
 func TestPubSub(t *testing.T) {
 
-ps := pubsub.New[string]()
+ps := New[string]()
 wg := new(sync.WaitGroup)
 rcvCount := new(atomic.Int64)
 msg := "hello world"
@@ -31,7 +30,6 @@ func TestPubSub(t *testing.T) {
 t.Errorf("ch1 got incorrect message; want %q, got %q", msg, m)
 }
 }
-fmt.Println("1")
 }()
 
 ch2, unsub2 := ps.Subscribe()
@@ -46,7 +44,6 @@ func TestPubSub(t *testing.T) {
 t.Errorf("ch2 got incorrect message; want %q, got %q", msg, m)
 }
 }
-fmt.Println("2")
 }()
 
 ch3, unsub3 := ps.Subscribe()
@@ -58,7 +55,6 @@ func TestPubSub(t *testing.T) {
 for range ch3 {
 t.Errorf("ch3 got message, didn't expect any")
 }
-fmt.Println("3")
 }()
 
 ps.Publish(msg)
@@ -71,3 +67,22 @@ func TestPubSub(t *testing.T) {
 t.Errorf("incorrect message count; want %d, got %d", want, got)
 }
 }
+
+func TestPubSubFinalizer(t *testing.T) {
+
+// Create the PubSub inside an inner scope
+// so the pointer becomes unreachable when we leave the block.
+done := func() <-chan struct{} {
+p := New[int]()
+return p.done
+}()
+
+runtime.GC()
+
+select {
+case <-done:
+// Success.
+case <-time.After(500 * time.Millisecond):
+t.Fatal("finalizer did not run")
+}
+}