org.apache.spark.util.KeyLock.scala Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.spark.util
import java.util.concurrent.ConcurrentHashMap
/**
* A special locking mechanism to provide locking with a given key. By providing the same key
* (identity is tested using the `equals` method), we ensure there is only one `func` running at
* the same time.
*
* @tparam K the type of key to identify a lock. This type must implement `equals` and `hashCode`
* correctly as it will be the key type of an internal Map.
*/
private[spark] class KeyLock[K] {
private val lockMap = new ConcurrentHashMap[K, AnyRef]()
private def acquireLock(key: K): Unit = {
while (true) {
val lock = lockMap.putIfAbsent(key, new Object)
if (lock == null) return
lock.synchronized {
while (lockMap.get(key) eq lock) {
lock.wait()
}
}
}
}
private def releaseLock(key: K): Unit = {
val lock = lockMap.remove(key)
lock.synchronized {
lock.notifyAll()
}
}
/**
* Run `func` under a lock identified by the given key. Multiple calls with the same key
* (identity is tested using the `equals` method) will be locked properly to ensure there is only
* one `func` running at the same time.
*/
def withLock[T](key: K)(func: => T): T = {
if (key == null) {
throw new NullPointerException("key must not be null")
}
acquireLock(key)
try {
func
} finally {
releaseLock(key)
}
}
}