https://issues.apache.org/jira/browse/AMQ-5256 - fix spurious amqp ioexception on concurrent connection protocol discrimination, client would see a hang on open. additional test

activemq-amqp/src/main/java/org/apache/activemq/transport/amqp/AMQPProtocolDiscriminator.java

@@ -59,7 +59,7 @@ public class AMQPProtocolDiscriminator implements IAmqpProtocolConverter {
 
     }
 
-    static final private ArrayList<Command> pendingCommands = new ArrayList<Command>();
+    final private ArrayList<Command> pendingCommands = new ArrayList<Command>();
 
     public AMQPProtocolDiscriminator(AmqpTransport transport) {
         this.transport = transport;

activemq-amqp/src/test/java/org/apache/activemq/transport/amqp/bugs/AMQ5256Test.java

@@ -0,0 +1,68 @@
+/**
+ * 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.activemq.transport.amqp.bugs;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import javax.jms.Connection;
+import javax.jms.JMSException;
+import org.apache.activemq.transport.amqp.AmqpTestSupport;
+import org.apache.qpid.amqp_1_0.jms.impl.ConnectionFactoryImpl;
+import org.junit.Test;
+
+
+import static org.junit.Assert.assertTrue;
+
+public class AMQ5256Test extends AmqpTestSupport {
+
+    @Override
+    protected boolean isUseTcpConnector() {
+        return true;
+    }
+
+    @Override
+    protected boolean isUseNioPlusSslConnector() {
+        return false;
+    }
+
+    @Test(timeout = 40 * 1000)
+    public void testParallelConnect() throws Exception {
+        final int numThreads = 80;
+        ExecutorService executorService = Executors.newFixedThreadPool(numThreads);
+        for (int i = 0; i < numThreads; i++) {
+            executorService.execute(new Runnable() {
+                @Override
+                public void run() {
+
+                    try {
+                        final ConnectionFactoryImpl connectionFactory = new ConnectionFactoryImpl("localhost", port, "admin", "password", null, isUseSslConnector());
+                        Connection connection = connectionFactory.createConnection();
+                        connection.start();
+                        connection.close();
+                    } catch (JMSException e) {
+                        e.printStackTrace();
+                    }
+                }
+            });
+        }
+
+        executorService.shutdown();
+        assertTrue("executor done on time", executorService.awaitTermination(30, TimeUnit.SECONDS));
+
+    }
+}