github.com/unigraph-dev/dgraph@v1.1.1-0.20200923154953-8b52b426f765/dgraph/cmd/bulk/shard_map.go (about)

     1  /*
     2   * Copyright 2017-2018 Dgraph Labs, Inc. and Contributors
     3   *
     4   * Licensed under the Apache License, Version 2.0 (the "License");
     5   * you may not use this file except in compliance with the License.
     6   * You may obtain a copy of the License at
     7   *
     8   *     http://www.apache.org/licenses/LICENSE-2.0
     9   *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  
    17  package bulk
    18  
    19  import "sync"
    20  
    21  type shardMap struct {
    22  	sync.RWMutex
    23  	numShards   int
    24  	predToShard map[string]int
    25  	nextShard   int
    26  }
    27  
    28  func newShardMap(numShards int) *shardMap {
    29  	return &shardMap{
    30  		numShards:   numShards,
    31  		predToShard: make(map[string]int),
    32  	}
    33  }
    34  
    35  func (m *shardMap) shardFor(pred string) int {
    36  	m.RLock()
    37  	shard, ok := m.predToShard[pred]
    38  	m.RUnlock()
    39  	if ok {
    40  		return shard
    41  	}
    42  
    43  	m.Lock()
    44  	defer m.Unlock()
    45  	shard, ok = m.predToShard[pred]
    46  	if ok {
    47  		return shard
    48  	}
    49  
    50  	shard = m.nextShard
    51  	m.predToShard[pred] = shard
    52  	m.nextShard = (m.nextShard + 1) % m.numShards
    53  	return shard
    54  }