The CLU search exit routine allows you to customize the logon manager's load balancing capabilities to meet the needs of your installation. The exit is called for initialization at the completion of logon manager initialization. The logon manager provides information about the session and the contending CLUs to the exit. The logon manager invokes the exit to compare all contending CLUs and to select the best CLU to service the application program. There is one exception — if the session request is being tried again, the CLU search exit is not called for any CLUs that have already failed. A list of CLUs that have failed is presented in the REQTAIL RU.

If there is only one contending CLU, the exit is called with information about only that CLU. If there is more than one contending CLU, the exit compares them a pair at a time. In each iteration, the exit selects the better of the two CLUs to be the current best CLU. In the first iteration, the current best CLU is the first contending CLU the logon manager encounters. In each subsequent iteration, the exit compares the current best CLU from the previous iteration to another contending CLU. The exit continues to compare pairs of CLUs until there are no more contending CLUs. At that point, the exit returns the name of the better CLU from the final iteration to the logon manager as the best CLU. If no best CLU is found after the list of possible CLUs is exhausted, the session request fails.

In the sample CLU search exit, the logon manager ensures that the contending CLUs meet certain minimum requirements. These requirements vary, depending on whether the session request comes from a dependent SLU, an independent or dependent PLU, or TPF. For a discussion of the requirements, see Criteria for contending CLUs.

The CLU search exit returns the name of the best CLU to the logon manger. For volatile USERVARs in PLU-initiated sessions, the logon manager finds the application program LU name associated with the best CLU and returns that name to the REQTAIL macro. The REQTAIL macro returns the name to the USERVAR exit.

The sample CLU search exit routine is stored in SYS1.SAMPLIB under the module name ELMCLUEX. If you write your own CLU search routine instead of using the sample, the following topics contain information you need. You might also want to see Sample CLU search exit routine for TPF sessions.