add UpdateSuffixarray and refactor TruncIndex

This commit refactors TruncIndex to make it possible to add container
ids to the TruncIndex without updating the Suffixarray.

This is useful during the Docker daemon's startup when we don't want to
update the Suffixarray for every container we add.

Add continues to function like before.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)

utils/utils.go

@@ -493,9 +493,7 @@ func NewTruncIndex(ids []string) (idx *TruncIndex) {
 	return
 }
 
-func (idx *TruncIndex) Add(id string) error {
-	idx.Lock()
-	defer idx.Unlock()
+func (idx *TruncIndex) addId(id string) error {
 	if strings.Contains(id, " ") {
 		return fmt.Errorf("Illegal character: ' '")
 	}
@@ -504,10 +502,31 @@ func (idx *TruncIndex) Add(id string) error {
 	}
 	idx.ids[id] = true
 	idx.bytes = append(idx.bytes, []byte(id+" ")...)
+	return nil
+}
+
+func (idx *TruncIndex) Add(id string) error {
+	idx.Lock()
+	defer idx.Unlock()
+	if err := idx.addId(id); err != nil {
+		return err
+	}
 	idx.index = suffixarray.New(idx.bytes)
 	return nil
 }
 
+func (idx *TruncIndex) AddWithoutSuffixarrayUpdate(id string) error {
+	idx.Lock()
+	defer idx.Unlock()
+	return idx.addId(id)
+}
+
+func (idx *TruncIndex) UpdateSuffixarray() {
+	idx.Lock()
+	defer idx.Unlock()
+	idx.index = suffixarray.New(idx.bytes)
+}
+
 func (idx *TruncIndex) Delete(id string) error {
 	idx.Lock()
 	defer idx.Unlock()