[MNG-7156] Parallel build can cause issues between clean and forked g…

maven-core/src/main/java/org/apache/maven/execution/LockingEventSpy.java

@@ -0,0 +1,98 @@
+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 built concurrently.
+ * This case can happen when running parallel builds with forked lifecycles.
+ */
+@Singleton
+@Named
+@Typed( EventSpy.class )
+public class LockingEventSpy extends AbstractEventSpy
+{
+
+    private static final Object LOCKS_KEY = new Object();
+
+    private final Logger logger = LoggerFactory.getLogger( getClass() );
+
+    @Override
+    public void onEvent( Object event ) throws Exception
+    {
+        if ( event instanceof ExecutionEvent )
+        {
+            ExecutionEvent executionEvent = ( ExecutionEvent ) event;
+            switch ( executionEvent.getType() )
+            {
+            case ProjectStarted:
+            case ForkedProjectStarted:
+                Lock lock = getLock( executionEvent );
+                if ( !lock.tryLock() )
+                {
+                    logger.debug( "Suspending concurrent execution of project '{}'", executionEvent.getProject() );
+                    lock.lockInterruptibly();
+                    logger.debug( "Resuming execution of project '{}'", executionEvent.getProject() );
+                }
+                break;
+            case ProjectSucceeded:
+            case ProjectFailed:
+            case ForkedProjectSucceeded:
+            case ForkedProjectFailed:
+                getLock( executionEvent ).unlock();
+                break;
+            default:
+                break;
+            }
+        }
+    }
+
+    @SuppressWarnings( { "unchecked", "rawtypes" } )
+    private Lock getLock( ExecutionEvent event )
+    {
+        SessionData data = event.getSession().getRepositorySession().getData();
+        Map<MavenProject, Lock> locks = ( Map ) data.get( LOCKS_KEY );
+        // initialize the value if not already done (in case of a concurrent access) to the method
+        if ( locks == null )
+        {
+            // the call to data.set(k, null, v) is effectively a call to data.putIfAbsent(k, v)
+            data.set( LOCKS_KEY, null, new ConcurrentHashMap<>() );
+            locks = ( Map ) data.get( LOCKS_KEY );
+        }
+        return locks.computeIfAbsent( event.getProject(), p -> new ReentrantLock() );
+    }
+
+}