github.com/insionng/yougam@v0.0.0-20170714101924-2bc18d833463/libraries/pingcap/tidb/util/segmentmap/segmentmap.go (about)

     1  // Copyright 2015 PingCAP, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package segmentmap
    15  
    16  import (
    17  	"hash/crc32"
    18  
    19  	"github.com/insionng/yougam/libraries/juju/errors"
    20  )
    21  
    22  // SegmentMap is used for handle a big map slice by slice.
    23  // It's not thread safe.
    24  type SegmentMap struct {
    25  	size int64
    26  	maps []map[string]interface{}
    27  
    28  	crcTable *crc32.Table
    29  }
    30  
    31  // NewSegmentMap create a new SegmentMap.
    32  func NewSegmentMap(size int64) (*SegmentMap, error) {
    33  	if size <= 0 {
    34  		return nil, errors.Errorf("Invalid size: %d", size)
    35  	}
    36  
    37  	sm := &SegmentMap{
    38  		maps: make([]map[string]interface{}, size),
    39  		size: size,
    40  	}
    41  	for i := int64(0); i < size; i++ {
    42  		sm.maps[i] = make(map[string]interface{})
    43  	}
    44  
    45  	sm.crcTable = crc32.MakeTable(crc32.Castagnoli)
    46  	return sm, nil
    47  }
    48  
    49  // Get is the same as map[k].
    50  func (sm *SegmentMap) Get(key []byte) (interface{}, bool) {
    51  	idx := int64(crc32.Checksum(key, sm.crcTable)) % sm.size
    52  	val, ok := sm.maps[idx][string(key)]
    53  	return val, ok
    54  }
    55  
    56  // GetSegment gets the map specific by index.
    57  func (sm *SegmentMap) GetSegment(index int64) (map[string]interface{}, error) {
    58  	if index >= sm.size || index < 0 {
    59  		return nil, errors.Errorf("index out of bound: %d", index)
    60  	}
    61  
    62  	return sm.maps[index], nil
    63  }
    64  
    65  // Set if key not exists, returns whether already exists.
    66  func (sm *SegmentMap) Set(key []byte, value interface{}, force bool) bool {
    67  	idx := int64(crc32.Checksum(key, sm.crcTable)) % sm.size
    68  	k := string(key)
    69  	_, exist := sm.maps[idx][k]
    70  	if exist && !force {
    71  		return exist
    72  	}
    73  
    74  	sm.maps[idx][k] = value
    75  	return exist
    76  }
    77  
    78  // SegmentCount returns how many inner segments.
    79  func (sm *SegmentMap) SegmentCount() int64 {
    80  	return sm.size
    81  }