Cooperative Processing Commands › Understanding Conversation States › Conversation States in a Successful Data Transfer

Conversation States in a Successful Data Transfer

In the following diagram, for example, Dialog A on the PC establishes a conversation with Dialog B on the mainframe. Dialog A sends a request for employee information to Dialog B. Dialog B processes the request and returns a reply. Matching data is found and returned. This is the same application shown in the flowchart earlier in this chapter.

The state changes are noted under the communications commands. Refer back to the previous flowchart and the sample code if you wish. You can see that Dialog B uses a RECEIVE-AND-WAIT to switch the line (changing from receive to send state in preparation for returning data to the PC). Also note the state changes necessary to deallocate the conversation. (Here, WR represents the WHAT-RECEIVED system field.)

A Successful Transaction

Dialog A                          Dialog B

(A1) ALLOCATE                     (B1) CONTROL SESSION
  State (reset to send)             State (receive)

(A2) SEND-DATA Emp-id             (B2) RECEIVE-AND-WAIT Emp-id
  State (send)                      State (receive)
                                    WR=DATA-COMPLETE
(A3) RECEIVE-AND-WAIT Emp-data
  State (send to receive)         (B3) RECEIVE-AND-WAIT
                                    State (receive to send)
                                    WR=SEND

(A6) RECEIVE-AND-WAIT.            (B5) SEND-DATA Emp-data
  State (receive to                 State (send)
         deallocate)

 (A7) DEALLOCATE                  (B6) DEALLOCATE
   State (deallocate to             State (send to reset)
          reset)

In this transaction:

• (A1) initiates conversation with ALLOCATE.
• (B1) acknowledges conversation with CONTROL SESSION.
• (B2) prepares to receive a request with RECEIVE-AND-WAIT.
• (A2) issues SEND-DATA with the employee id as a parameter.
• (B3) prepares to send a reply with RECEIVE-AND-WAIT. This command switches the line. Dialog B changes state from receive to send.
• (A3) prepares to receive the employee data.
• (B5) returns employee data to Dialog A with SEND-DATA. Dialog A tests for the PROG-ERROR condition, but does not find it. Dialog A checks that the data is complete (APPCCODE=OK and WR=DATA-COMPLETE).
• (A6) once the data is successfully received, RECEIVE-AND-WAIT prepares to deallocate resources verifying that Dialog B (currently in control) is ready to end the conversation.
• (B6) flushes the communications buffer and terminates the conversation with DEALLOCATE.
• (A7) releases local resources with DEALLOCATE LOCAL.