move FieldCache into upsidedown (#1513)

previous the FieldCache type was in the index package,
but it is only used by upsidedown, so we relocate it there.

index/upsidedown/field_cache.go

@@ -0,0 +1,88 @@
+//  Copyright (c) 2015 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package upsidedown
+
+import (
+	"sync"
+)
+
+type FieldCache struct {
+	fieldIndexes   map[string]uint16
+	indexFields    []string
+	lastFieldIndex int
+	mutex          sync.RWMutex
+}
+
+func NewFieldCache() *FieldCache {
+	return &FieldCache{
+		fieldIndexes:   make(map[string]uint16),
+		lastFieldIndex: -1,
+	}
+}
+
+func (f *FieldCache) AddExisting(field string, index uint16) {
+	f.mutex.Lock()
+	f.addLOCKED(field, index)
+	f.mutex.Unlock()
+}
+
+func (f *FieldCache) addLOCKED(field string, index uint16) uint16 {
+	f.fieldIndexes[field] = index
+	if len(f.indexFields) < int(index)+1 {
+		prevIndexFields := f.indexFields
+		f.indexFields = make([]string, int(index)+16)
+		copy(f.indexFields, prevIndexFields)
+	}
+	f.indexFields[int(index)] = field
+	if int(index) > f.lastFieldIndex {
+		f.lastFieldIndex = int(index)
+	}
+	return index
+}
+
+// FieldNamed returns the index of the field, and whether or not it existed
+// before this call.  if createIfMissing is true, and new field index is assigned
+// but the second return value will still be false
+func (f *FieldCache) FieldNamed(field string, createIfMissing bool) (uint16, bool) {
+	f.mutex.RLock()
+	if index, ok := f.fieldIndexes[field]; ok {
+		f.mutex.RUnlock()
+		return index, true
+	} else if !createIfMissing {
+		f.mutex.RUnlock()
+		return 0, false
+	}
+	// trade read lock for write lock
+	f.mutex.RUnlock()
+	f.mutex.Lock()
+	// need to check again with write lock
+	if index, ok := f.fieldIndexes[field]; ok {
+		f.mutex.Unlock()
+		return index, true
+	}
+	// assign next field id
+	index := f.addLOCKED(field, uint16(f.lastFieldIndex+1))
+	f.mutex.Unlock()
+	return index, false
+}
+
+func (f *FieldCache) FieldIndexed(index uint16) (field string) {
+	f.mutex.RLock()
+	if int(index) < len(f.indexFields) {
+		field = f.indexFields[int(index)]
+	}
+	f.mutex.RUnlock()
+	return field
+}

index/upsidedown/upsidedown.go

@@ -54,7 +54,7 @@ type UpsideDownCouch struct {
 	storeName     string
 	storeConfig   map[string]interface{}
 	store         store.KVStore
-	fieldCache    *index.FieldCache
+	fieldCache    *FieldCache
 	analysisQueue *index.AnalysisQueue
 	stats         *indexStat
 
@@ -74,7 +74,7 @@ type docBackIndexRow struct {
 func NewUpsideDownCouch(storeName string, storeConfig map[string]interface{}, analysisQueue *index.AnalysisQueue) (index.Index, error) {
 	rv := &UpsideDownCouch{
 		version:       Version,
-		fieldCache:    index.NewFieldCache(),
+		fieldCache:    NewFieldCache(),
 		storeName:     storeName,
 		storeConfig:   storeConfig,
 		analysisQueue: analysisQueue,