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