[GitHub] [maven] gnodet commented on a change in pull request #476: [MNG-7156] Parallel build can cause issues between clean and forked g…

[GitBox <gi...@apache.org>]

gnodet commented on a change in pull request #476:
URL: https://github.com/apache/maven/pull/476#discussion_r646178535



##########
File path: maven-core/src/main/java/org/apache/maven/execution/LockingEventSpy.java
##########
@@ -0,0 +1,96 @@
+package org.apache.maven.execution;
+
+/*
+ * 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.
+ */
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import javax.inject.Named;
+import javax.inject.Singleton;
+
+import org.apache.maven.eventspy.AbstractEventSpy;
+import org.apache.maven.eventspy.EventSpy;
+import org.apache.maven.project.MavenProject;
+import org.eclipse.aether.SessionData;
+import org.eclipse.sisu.Typed;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * EventSpy implementation that provides a per-project locking mechanism
+ * to make sure a given project can not be build twice concurrently.
+ * This case can happen when running parallel builds with forked lifecycles.
+ */
+@Singleton
+@Named
+@Typed( EventSpy.class )
+public class LockingEventSpy extends AbstractEventSpy
+{
+
+    private final Logger logger = LoggerFactory.getLogger( getClass() );
+
+    private static final Object LOCKS_KEY = new Object();
+
+    @SuppressWarnings( { "unchecked", "rawtypes" } )
+    private Lock getLock( ExecutionEvent event )
+    {
+        SessionData data = event.getSession().getRepositorySession().getData();
+        Map<MavenProject, Lock> locks = ( Map ) data.get( LOCKS_KEY );
+        if ( locks == null )
+        {
+            data.set( LOCKS_KEY, null, new ConcurrentHashMap<>() );
+            locks = ( Map ) data.get( LOCKS_KEY );
+        }
+        return locks.computeIfAbsent( event.getProject(), p -> new ReentrantLock() );
+    }
+
+    @Override
+    public void onEvent( Object event ) throws Exception
+    {
+        if ( event instanceof ExecutionEvent )
+        {
+            ExecutionEvent ee = ( ExecutionEvent ) event;
+            switch ( ee.getType() )
+            {
+            case ProjectStarted:
+            case ForkedProjectStarted:
+                Lock lock = getLock( ee );
+                if ( !lock.tryLock() )
+                {
+                    logger.warn( "Suspending concurrent execution of project " + ee.getProject() );
+                    getLock( ee ).lockInterruptibly();
+                    logger.warn( "Resuming execution of project " + ee.getProject() );
+                }
+                break;
+            case ProjectSucceeded:
+            case ProjectFailed:

Review comment:
       My understanding is the `ProjectSkipped` is send after a failure and in such a case, the project is... skipped, so there's no need to lock / unlock, especially as the `ProjectStarted` event is not sent in such cases.




-- 
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.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org