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// 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 index
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
}
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