Made exchange declaration fashionably late

Author: 0x6e6562

test/src/com/rabbitmq/examples/ProducerMain.java

@@ -148,16 +148,22 @@ private void runIt() throws IOException {
 
         String queueName = "test queue";
         _channel.queueDeclare(_ticket, queueName, shouldPersist());
-
-        String exchangeName = "test completion";
-        _channel.exchangeDeclare(_ticket, exchangeName, "fanout", false, false, true, null);
-
+        
         if (shouldCommit()) {
             _channel.txSelect();
         }
         sendBatch(queueName);
 
         if (_sendCompletion) {
+            // Declaring this exchange as auto-delete is a bit dodgy because of a
+            // race condition with the consumer declaring the same exchange to be
+            // auto-delete and hence pulling the rug out from underneath the producer's
+            // feet.
+            // Hence we're delaying a possible re-declaration until as late as possible.
+            // Ideally you would use a global lock around both critical sections,
+            // but thread safety has gone out of fashion these days.
+            String exchangeName = "test completion";
+            _channel.exchangeDeclare(_ticket, exchangeName, "fanout", false, false, true, null);
             _channel.basicPublish(_ticket, exchangeName, "", MessageProperties.BASIC, new byte[0]);
             if (shouldCommit())
                 _channel.txCommit();