On a successful return from the first of a sequence of extended ECI calls for a LUW, the user application is returned a LUW identifier corresponding to an instance of a CICS® mirror transaction. Specifying this LUW identifier in subsequent ECI calls means that these calls will be processed by the same CICS mirror transaction. All program link calls for the same LUW are sent to the same server.
When the user application makes an ECI commit or rollback call, the CICS server attempts to commit or back out changes to recoverable resources. The user application is advised whether or not the attempt was successful. If a LUW is outstanding (incomplete), the user application should issue an extended ECI commit or rollback call to the CICS server. If the execution of a user application completes without committing or rolling back an outstanding LUW, the CICS Transaction Gateway or CICS Universal Client attempts to back out the LUW.
If an extended ECI call fails, the user application must check if a nonzero LUW identifier was returned. If so, this indicates that the LUW is still outstanding and should be committed or rolled back. If not, the problem is a lost communications link with the CICS server.
An ECI user application using an extended LUW might cause other user applications to be suspended waiting for CICS resources, which are held for the duration of the LUW.