Has the application run successfully before?

Use the information in this topic to help diagnose common problems with applications.

If the problem appears to involve one particular application, consider whether the application has run successfully before.

• Have any changes been made to the application since it last ran successfully?

  If so, it is likely that the error lies somewhere in the new or modified part of the application. Take a look at the changes and see if we can find an obvious reason for the problem. Is it possible to retry using a back level of the application?

• Have all the functions of the application been fully exercised before?

  Could it be that the problem occurred when part of the application that had never been invoked before was used for the first time? If so, it is likely that the error lies in that part of the application. Try to find out what the application was doing when it failed, and check the source code in that part of the program for errors.

  If a program has been run successfully on many previous occasions, check the current queue status and the files that were being processed when the error occurred. It is possible that they contain some unusual data value that invokes a rarely-used path in the program.

• Does the application check all return codes?

  Has your IBM MQ system been changed, perhaps in a minor way, such that our application does not check the return codes it receives as a result of the change. For example, does our application assume that the queues it accesses can be shared? If a queue has been redefined as exclusive, can our application deal with return codes indicating that it can no longer access that queue?

• Does the application run on other IBM MQ systems?

  Could it be that there is something different about the way that this IBM MQ system is set up that is causing the problem? For example, have the queues been defined with the same message length or priority?

Before you look at the code, and depending upon which programming language the code is written in, examine the output from the translator, or the compiler and linkage editor, to see if any errors have been reported.

If our application fails to translate, compile, or link-edit into the load library, it will also fail to run if you attempt to invoke it. See Developing applications for information about building our application.

If the documentation shows that each of these steps was accomplished without error, consider the coding logic of the application. Do the symptoms of the problem indicate the function that is failing and, therefore, the piece of code in error? See the following section for some examples of common errors that cause problems with IBM MQ applications.

Common programming errors

• Assuming that queues can be shared, when they are in fact exclusive.
• Passing incorrect parameters in an MQI call.
• Passing insufficient parameters in an MQI call. This might mean that IBM MQ cannot set up completion and reason codes for your application to process.
• Failing to check return codes from MQI requests.
• Passing variables with incorrect lengths specified.
• Passing parameters in the wrong order.
• Failing to initialize MsgId and CorrelId correctly.
• Failing to initialize Encoding and CodedCharSetId following MQRC_TRUNCATED_MSG_ACCEPTED.