Merge pull request #14 from segmentio/pelletier/resize

Resize method

cache.go

@@ -399,6 +399,28 @@ func (cache *Cache) Stats() Stats {
 	}
 }
 
+// Resize the cache to hold at most n entries. If n is smaller than the current
+// size, entries are evicted to fit the new size. It errors if n <= 0.
+func (cache *Cache) Resize(n int) error {
+	if n <= 0 {
+		return errors.New("must supply a positive capacity to Resize")
+	}
+
+	cache.mutex.Lock()
+	defer cache.mutex.Unlock()
+	c := cache.capacity
+	cache.capacity = n
+
+	for i := 0; i < c-n; i++ {
+		successful := cache.evictOldest()
+		if !successful {
+			break
+		}
+	}
+
+	return nil
+}
+
 func (cache *Cache) deleteExpired() {
 	keys := cache.Keys()
 

cache_test.go

@@ -354,6 +354,37 @@ func TestActiveExpiration(t *testing.T) {
 	assert.True(t, duration < time.Millisecond*2)
 }
 
+func TestResize(t *testing.T) {
+	cache := New(Config{
+		Capacity: 2,
+	})
+	cache.Set("a", 1)
+	cache.Set("b", 1)
+
+	cache.Resize(2) // no-op
+
+	assert.True(t, cache.Has("a"))
+	assert.True(t, cache.Has("b"))
+
+	cache.Set("c", 1)
+	assert.False(t, cache.Has("a"))
+	assert.True(t, cache.Has("b"))
+	assert.True(t, cache.Has("c"))
+
+	cache.Resize(1)
+	assert.False(t, cache.Has("a"))
+	assert.False(t, cache.Has("b"))
+	assert.True(t, cache.Has("c"))
+
+	cache.Resize(2)
+	cache.Set("d", 1)
+
+	assert.False(t, cache.Has("a"))
+	assert.False(t, cache.Has("b"))
+	assert.True(t, cache.Has("c"))
+	assert.True(t, cache.Has("d"))
+}
+
 func TestStats(t *testing.T) {
 	t.Run("reports capacity", func(t *testing.T) {
 		cache := New(Config{Capacity: 100})