Make the add method thread safe

debounce.go

@@ -1,4 +1,4 @@
-// Copyright © 2016 Bjørn Erik Pedersen <[email protected]>.
+// Copyright © 2019 Bjørn Erik Pedersen <[email protected]>.
 //
 // Use of this source code is governed by an MIT-style
 // license that can be found in the LICENSE file.
@@ -9,6 +9,7 @@
 package debounce
 
 import (
+	"sync"
 	"time"
 )
 
@@ -26,11 +27,15 @@ func New(after time.Duration) func(f func()) {
 }
 
 type debouncer struct {
+	mu    sync.Mutex
 	after time.Duration
 	timer *time.Timer
 }
 
 func (d *debouncer) add(f func()) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
 	if d.timer != nil {
 		d.timer.Stop()
 	}

debounce_test.go

@@ -2,6 +2,7 @@ package debounce_test
 
 import (
 	"fmt"
+	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -58,6 +59,31 @@ func TestDebounce(t *testing.T) {
 	}
 }
 
+func TestDebounceConcurrentAdd(t *testing.T) {
+	var wg sync.WaitGroup
+
+	var flag uint64
+
+	debounced := debounce.New(100 * time.Millisecond)
+
+	for i := 0; i < 10; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			debounced(func() {
+				atomic.CompareAndSwapUint64(&flag, 0, 1)
+			})
+		}()
+	}
+	wg.Wait()
+
+	time.Sleep(500 * time.Millisecond)
+	c := int(atomic.LoadUint64(&flag))
+	if c != 1 {
+		t.Error("Flag not set")
+	}
+}
+
 // Issue #1
 func TestDebounceDelayed(t *testing.T) {
 
@@ -75,7 +101,7 @@ func TestDebounceDelayed(t *testing.T) {
 
 	debounced(f1)
 
-	time.Sleep(110 * time.Millisecond)
+	time.Sleep(200 * time.Millisecond)
 
 	c1 := int(atomic.LoadUint64(&counter1))
 	if c1 != 1 {