JoshRosen commented on code in PR #48391: URL: https://github.com/apache/spark/pull/48391#discussion_r1796194610
########## core/src/main/scala/org/apache/spark/util/Lazy.scala: ########## @@ -0,0 +1,43 @@ +/* + * 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.io.ObjectOutputStream + +/** + * Construct to lazily initialize a variable. + * This may be helpful for avoiding deadlocks in certain scenarios. For example, + * a) Thread 1 entered a synchronized method, grabbing a coarse lock on the parent object. + * b) Thread 2 gets spawned off, and tries to initialize a lazy value on the same parent object + * (in our case, this was the logger). This causes scala to also try to grab a coarse lock on + * the parent object. + * c) If thread 1 waits for thread 2 to join, a deadlock occurs. Review Comment: Scala 3 uses a different implementation of lazy vals which doesn't have this problem. You can reference SIP-20 / https://docs.scala-lang.org/scala3/reference/changed-features/lazy-vals-init.html which has some pointers to more references on this class of deadlock issue. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
