diff --git a/its/core-it-suite/src/test/java/org/apache/maven/it/IntegrationTestSuite.java b/its/core-it-suite/src/test/java/org/apache/maven/it/IntegrationTestSuite.java
index 3ecb4b07b7..34aee23e12 100644
--- a/its/core-it-suite/src/test/java/org/apache/maven/it/IntegrationTestSuite.java
+++ b/its/core-it-suite/src/test/java/org/apache/maven/it/IntegrationTestSuite.java
@@ -85,6 +85,7 @@ public class IntegrationTestSuite
// suite.addTestSuite( MavenIT0109ReleaseUpdateTest.class );
// suite.addTestSuite( MavenIT0108SnapshotUpdateTest.class ); -- MNG-3137
+ suite.addTestSuite( MavenITmng4544ActiveComponentCollectionThreadSafeTest.class );
suite.addTestSuite( MavenITmng4500NoUpdateOfTimestampedSnapshotsTest.class );
suite.addTestSuite( MavenITmng4498IgnoreBrokenMetadataTest.class );
suite.addTestSuite( MavenITmng4489MirroringOfExtensionRepoTest.class );
diff --git a/its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng4544ActiveComponentCollectionThreadSafeTest.java b/its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng4544ActiveComponentCollectionThreadSafeTest.java
new file mode 100644
index 0000000000..4894469223
--- /dev/null
+++ b/its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng4544ActiveComponentCollectionThreadSafeTest.java
@@ -0,0 +1,62 @@
+package org.apache.maven.it;
+
+/*
+ * 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 org.apache.maven.it.Verifier;
+import org.apache.maven.it.util.ResourceExtractor;
+
+import java.io.File;
+import java.util.Properties;
+
+/**
+ * This is a test set for MNG-4544.
+ *
+ * @author Benjamin Bentmann
+ */
+public class MavenITmng4544ActiveComponentCollectionThreadSafeTest
+ extends AbstractMavenIntegrationTestCase
+{
+
+ public MavenITmng4544ActiveComponentCollectionThreadSafeTest()
+ {
+ super( "[2.0.3,3.0-alpha-1),[3.0-alpha-7,)" );
+ }
+
+ /**
+ * Test that concurrent access to active component collections is thread-safe.
+ */
+ public void testit()
+ throws Exception
+ {
+ File testDir = ResourceExtractor.simpleExtractResources( getClass(), "/mng-4544" );
+
+ Verifier verifier = new Verifier( testDir.getAbsolutePath() );
+ verifier.setAutoclean( false );
+ verifier.deleteDirectory( "target" );
+ verifier.executeGoal( "validate" );
+ verifier.verifyErrorFreeLog();
+ verifier.resetStreams();
+
+ Properties props = verifier.loadProperties( "target/thread.properties" );
+ assertEquals( 0, Integer.parseInt( props.getProperty( "exceptions" ) ) );
+ assertEquals( 2, Integer.parseInt( props.getProperty( "components" ) ) );
+ }
+
+}
diff --git a/its/core-it-suite/src/test/resources/mng-4544/pom.xml b/its/core-it-suite/src/test/resources/mng-4544/pom.xml
new file mode 100644
index 0000000000..dc1ae3b4b3
--- /dev/null
+++ b/its/core-it-suite/src/test/resources/mng-4544/pom.xml
@@ -0,0 +1,55 @@
+
+
+
+
+
+ 4.0.0
+
+ org.apache.maven.its.mng4544
+ test
+ 0.1
+
+ Maven Integration Test :: MNG-4544
+
+ Test that concurrent access to active component collections is thread-safe.
+
+
+
+
+
+ org.apache.maven.its.plugins
+ maven-it-plugin-active-collection
+ 2.1-SNAPSHOT
+
+ target/thread.properties
+
+
+
+ test
+ validate
+
+ check-thread-safety
+
+
+
+
+
+
+
diff --git a/its/core-it-support/core-it-plugins/maven-it-plugin-active-collection/src/main/java/org/apache/maven/plugin/coreit/CheckThreadSafetyMojo.java b/its/core-it-support/core-it-plugins/maven-it-plugin-active-collection/src/main/java/org/apache/maven/plugin/coreit/CheckThreadSafetyMojo.java
new file mode 100644
index 0000000000..8be16e7991
--- /dev/null
+++ b/its/core-it-support/core-it-plugins/maven-it-plugin-active-collection/src/main/java/org/apache/maven/plugin/coreit/CheckThreadSafetyMojo.java
@@ -0,0 +1,188 @@
+package org.apache.maven.plugin.coreit;
+
+/*
+ * 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 org.apache.maven.plugin.AbstractMojo;
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.MojoFailureException;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+import java.util.Vector;
+
+/**
+ * Checks the thread-safe retrieval of components from active component collections.
+ *
+ * @goal check-thread-safety
+ * @phase validate
+ *
+ * @author Benjamin Bentmann
+ */
+public class CheckThreadSafetyMojo
+ extends AbstractMojo
+{
+
+ /**
+ * Project base directory used for manual path alignment.
+ *
+ * @parameter default-value="${basedir}"
+ * @readonly
+ */
+ private File basedir;
+
+ /**
+ * The available components, as a map.
+ *
+ * @component role="org.apache.maven.plugin.coreit.Component"
+ */
+ private Map componentMap;
+
+ /**
+ * The available components, as a list.
+ *
+ * @component role="org.apache.maven.plugin.coreit.Component"
+ */
+ private List componentList;
+
+ /**
+ * The path to the properties file to create.
+ *
+ * @parameter expression="${collections.outputFile}"
+ */
+ private File outputFile;
+
+ /**
+ * Runs this mojo.
+ *
+ * @throws MojoFailureException If the output file could not be created.
+ */
+ public void execute()
+ throws MojoExecutionException
+ {
+ Properties componentProperties = new Properties();
+
+ getLog().info( "[MAVEN-CORE-IT-LOG] Testing concurrent component access" );
+
+ final Map map = componentMap;
+ final List list = componentList;
+ final List go = new Vector();
+ final List exceptions = new Vector();
+
+ Thread[] threads = new Thread[2];
+ for ( int i = 0; i < threads.length; i++ )
+ {
+ // NOTE: The threads need to use different realms to trigger changes of the collections
+ final ClassLoader cl =
+ ( i % 2 ) == 0 ? getClass().getClassLoader() : MojoExecutionException.class.getClassLoader();
+ threads[i] = new Thread()
+ {
+ private final ClassLoader tccl = cl;
+
+ public void run()
+ {
+ getLog().info( "[MAVEN-CORE-IT-LOG] Thread " + this + " uses " + tccl );
+ Thread.currentThread().setContextClassLoader( tccl );
+ while ( go.isEmpty() )
+ {
+ // wait for start
+ }
+ for ( int j = 0; j < 10000; j++ )
+ {
+ try
+ {
+ for ( Iterator it = map.values().iterator(); it.hasNext(); )
+ {
+ it.next().toString();
+ }
+ for ( Iterator it = list.iterator(); it.hasNext(); )
+ {
+ it.next().toString();
+ }
+ }
+ catch ( Exception e )
+ {
+ getLog().warn( "[MAVEN-CORE-IT-LOG] Thread " + this + " encountered concurrency issue", e );
+ exceptions.add( e );
+ }
+ }
+ }
+ };
+ threads[i].start();
+ }
+
+ go.add( null );
+ for ( int i = 0; i < threads.length; i++ )
+ {
+ try
+ {
+ threads[i].join();
+ }
+ catch ( InterruptedException e )
+ {
+ getLog().warn( "[MAVEN-CORE-IT-LOG] Interrupted while joining " + threads[i] );
+ }
+ }
+
+ componentProperties.setProperty( "components", Integer.toString( componentList.size() ) );
+ componentProperties.setProperty( "exceptions", Integer.toString( exceptions.size() ) );
+
+ if ( !outputFile.isAbsolute() )
+ {
+ outputFile = new File( basedir, outputFile.getPath() );
+ }
+
+ getLog().info( "[MAVEN-CORE-IT-LOG] Creating output file " + outputFile );
+
+ OutputStream out = null;
+ try
+ {
+ outputFile.getParentFile().mkdirs();
+ out = new FileOutputStream( outputFile );
+ componentProperties.store( out, "MAVEN-CORE-IT-LOG" );
+ }
+ catch ( IOException e )
+ {
+ throw new MojoExecutionException( "Output file could not be created: " + outputFile, e );
+ }
+ finally
+ {
+ if ( out != null )
+ {
+ try
+ {
+ out.close();
+ }
+ catch ( IOException e )
+ {
+ // just ignore
+ }
+ }
+ }
+
+ getLog().info( "[MAVEN-CORE-IT-LOG] Created output file " + outputFile );
+ }
+
+}