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/*
* Copyright 2017-2018 Dgraph Labs, Inc. and Contributors
*
* 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 bulk
import "sync"
type shardMap struct {
sync.RWMutex
numShards int
predToShard map[string]int
nextShard int
}
func newShardMap(numShards int) *shardMap {
return &shardMap{
numShards: numShards,
predToShard: make(map[string]int),
}
}
func (m *shardMap) shardFor(pred string) int {
m.RLock()
shard, ok := m.predToShard[pred]
m.RUnlock()
if ok {
return shard
}
m.Lock()
defer m.Unlock()
shard, ok = m.predToShard[pred]
if ok {
return shard
}
shard = m.nextShard
m.predToShard[pred] = shard
m.nextShard = (m.nextShard + 1) % m.numShards
return shard
}