Garbage collection alone cannot release all WebSphere MQ resources in a timely manner. This is especially true if the application needs to create many short-lived JMS objects at the Session level or lower. It is therefore important to call the close() methods of the various classes (QueueConnection, QueueSession, QueueSender, and QueueReceiver) when the resources are no longer required.
If an application using WebSphere MQ JMS finishes without calling Connection.close(), some JVMs will appear to hang. If this problem occurs, either edit the application to include a call to Connection.close(), or terminate the JVM by using the Ctrl-C keys.