markusthoemmes commented on a change in pull request #3240: Add a loadbalancer with local state and horizontal invoker sharding. URL: https://github.com/apache/incubator-openwhisk/pull/3240#discussion_r167275225
########## File path: common/scala/src/main/scala/whisk/common/ForcableSemaphore.scala ########## @@ -0,0 +1,116 @@ +/* + * 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 whisk.common + +import java.util.concurrent.locks.AbstractQueuedSynchronizer + +import scala.annotation.tailrec + +/** + * A Semaphore, which in addition to the usual features has means to force more clients to get permits. + * + * Like any usual Semaphore, this implementation will give away at most `maxAllowed` permits when used the "usual" way. + * In addition to that, it also has a `forceAcquire` method which will push the Semaphore's remaining permits into a + * negative value. Getting permits using `tryAcquire` will only be possible once the permits value is in a positive + * state again. + * + * As this is (now) only used for the loadbalancer's scheduling, this does not implement the "whole" Java Semaphore's + * interface but only the methods needed. + * + * @param maxAllowed maximum number of permits given away by `tryAcquire` + */ +class ForcableSemaphore(maxAllowed: Int) { + class Sync extends AbstractQueuedSynchronizer { + setState(maxAllowed) + + def permits: Int = getState + + @tailrec + override final def tryReleaseShared(releases: Int): Boolean = { + val current = getState + val next = current + releases + if (next < current) { // overflow + throw new Error("Maximum permit count exceeded") Review comment: As the comment indicates, this catches an integer overflow (overflowing numbers will become negative), so I'd say an exception is warranted. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
