Fix cleaner goroutine returning without closing the close channel

cache.go

@@ -66,68 +66,33 @@ func (c *Cache[K, V]) Close() {
 // cleaner handles removing expired keys. The chainAdd and chainDel channels are
 // handled here to prevent race conditions. This ensures the expiry timer can be
 // stopped before modifying the chain.
-//
-// The cleaner is stopped whenever the chain is empty due to there being no chain
-// to manage.
 func (c *Cache[K, V]) cleaner() {
-	// cleaner is always called from Set or Delete methods with a value sent on chainAdd or chainDel
-	select {
-	case node := <-c.chainAdd:
-		c.chainInsert(node)
-	case key := <-c.chainDel:
-		c.chainSplice(key)
-	default:
-		// skip if chainAdd or chainDel isn't ready
-	}
-
-	// at this point if the chain is empty then exit
-	if c.chain == nil {
-		return
-	}
-
-	// create a timer for the next expiry
-	t := time.NewTimer(timeUntil(c.chain.expires))
-
 	for {
 		select {
 		case <-c.close:
 			// exit the cleaner goroutine
 			return
 		case node := <-c.chainAdd:
-			// stop the timer safely
-			if !t.Stop() {
-				<-t.C
-			}
-			// the chain will not be empty after this insert so no check is required
 			c.chainInsert(node)
 		case key := <-c.chainDel:
-			// stop the timer safely
-			if !t.Stop() {
-				<-t.C
-			}
 			c.chainSplice(key)
-		case <-t.C:
-			// if there is no chain then kill the expiry scheduler
-			if c.chain == nil {
-				return
-			}
-
+		case <-c.nextExpiry():
 			// remove all expired entries
 			for c.chain != nil && c.chain.HasExpired() {
 				c.items.CompareAndDelete(c.chain.data, c.chain.item)
 				c.chain = c.chain.next
 			}
 		}
-
-		// if there is no chain then kill the expiry scheduler
-		if c.chain == nil {
-			return
-		}
-
-		t.Reset(timeUntil(c.chain.expires))
 	}
 }
 
+func (c *Cache[K, V]) nextExpiry() <-chan time.Time {
+	if c.chain == nil {
+		return make(chan time.Time)
+	}
+	return time.After(timeUntil(c.chain.expires))
+}
+
 func (c *Cache[K, V]) chainInsert(node keyed[K]) {
 	// quick path for an empty chain
 	if c.chain == nil {

cache_test.go

@@ -152,3 +152,21 @@ func TestCache_UpdateExpiry(t *testing.T) {
 	assert.True(t, b)
 	assert.Equal(t, "b", get)
 }
+
+func TestCache_ClearerDeath(t *testing.T) {
+	timeNow = func() time.Time { return time.Now() }
+
+	c := New[string, string]()
+
+	time.Sleep(10 * time.Millisecond)
+
+	var added bool
+	go func() {
+		c.chainAdd <- keyed[string]{item: item[string]{data: "a"}}
+		c.chainAdd <- keyed[string]{item: item[string]{data: "b"}}
+		added = true
+	}()
+
+	time.Sleep(10 * time.Millisecond)
+	assert.True(t, added)
+}