expvar: add Map.Delete

Fixes #13491

Change-Id: Ic0525d8ee90f47d0d23c1485919aee13d2400494
Reviewed-on: https://go-review.googlesource.com/c/139537
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/expvar/expvar.go

@@ -137,7 +137,7 @@ func (v *Map) Init() *Map {
 	return v
 }
 
-// updateKeys updates the sorted list of keys in v.keys.
+// addKey updates the sorted list of keys in v.keys.
 func (v *Map) addKey(key string) {
 	v.keysMu.Lock()
 	defer v.keysMu.Unlock()
@@ -199,6 +199,17 @@ func (v *Map) AddFloat(key string, delta float64) {
 	}
 }
 
+// Deletes the given key from the map.
+func (v *Map) Delete(key string) {
+	v.keysMu.Lock()
+	defer v.keysMu.Unlock()
+	i := sort.SearchStrings(v.keys, key)
+	if i < len(v.keys) && key == v.keys[i] {
+		v.keys = append(v.keys[:i], v.keys[i+1:]...)
+		v.m.Delete(key)
+	}
+}
+
 // Do calls f for each entry in the map.
 // The map is locked during the iteration,
 // but existing entries may be concurrently updated.

src/expvar/expvar_test.go

@@ -183,6 +183,43 @@ func TestMapInit(t *testing.T) {
 	}
 }
 
+func TestMapDelete(t *testing.T) {
+	RemoveAll()
+	colors := NewMap("bike-shed-colors")
+
+	colors.Add("red", 1)
+	colors.Add("red", 2)
+	colors.Add("blue", 4)
+
+	n := 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 2 {
+		t.Errorf("after two Add calls with distinct keys, Do should invoke f 2 times; got %v", n)
+	}
+
+	colors.Delete("red")
+	n = 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 1 {
+		t.Errorf("removed red, Do should invoke f 1 times; got %v", n)
+	}
+
+	colors.Delete("notfound")
+	n = 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 1 {
+		t.Errorf("attempted to remove notfound, Do should invoke f 1 times; got %v", n)
+	}
+
+	colors.Delete("blue")
+	colors.Delete("blue")
+	n = 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 0 {
+		t.Errorf("all keys removed, Do should invoke f 0 times; got %v", n)
+	}
+}
+
 func TestMapCounter(t *testing.T) {
 	RemoveAll()
 	colors := NewMap("bike-shed-colors")