Program link calls

An ECI request to call a program on a CICS® server results in a program link call to attach the CICS mirror transaction to run the server program.

ECI request program link calls can be synchronous or asynchronous:

Synchronous
Synchronous calls are blocking calls. The user application is suspended until the called server program has finished and a reply is received from CICS. The received reply is immediately available.
Asynchronous
Asynchronous calls are nonblocking calls. The user application gets control back without waiting for the called server program to finish. The reply from CICS can be retrieved later using one of the reply solicitation calls or a callback. See Retrieving replies from asynchronous ECI requests. An asynchronous program link call is outstanding until a reply solicitation call, or the callback, has retrieved the reply.

Synchronous and asynchronous program link calls can be nonextended or extended:

Nonextended
The CICS server program, not the user application, controls whether recoverable resources are committed or backed out. Each program link call corresponds to one CICS transaction. This is referred to as SYNCONRETURN.
Extended
The user application controls whether recoverable resources are committed or rolled back. Multiple calls are possible, allowing a logical unit of work (LUW) to be extended across successive ECI requests to the same CICS server. This is known as an extended logical unit of work (extended LUW).

CICS user applications are often concerned with updating recoverable resources. An LUW is the processing that a CICS server program performs between sync points. A sync point is the point at which all changes to recoverable resources that were made by a task since its last sync point are committed. LUW management is performed by the user application, using the commit and rollback functions:

Commit
Ends the current LUW and any changes made to recoverable resources are committed.
Rollback
Terminates the current LUW and backs out (rolls back) any changes made to recoverable resources since the previous sync point.

ECI-based communications between the CICS server and the CICS Transaction Gateway are known as conversations. A nonextended program link ECI call is one conversation. A series of extended ECI calls followed by a commit or rollback is one conversation.


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Timestamp icon Last updated: Tuesday, 19 November 2013


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