Terminal waits

When you use the WAIT option on a SEND command, CICS does not return control to your task until the output operation is complete.

When a task issues a SEND command without specifying WAIT, CICS can defer transmission of the output to optimize either its overall terminal handling or the transmissions for your task. When it does this, CICS saves the output message and makes your task dispatchable, so that it can continue executing. The ISSUE COPY and ISSUE ERASE commands, which also transmit output, work similarly without WAIT.

If you use the WAIT option, CICS does not return control to your task until the output operation is complete. This wait lengthens the elapsed time of your task, with attendant effects on response time and memory occupancy, but it ensures that your task knows whether there has been an error on the SEND before continuing. You can avoid some of this wait and still check the completion of the operation if you have processing to do after your SEND. You issue the SEND without WAIT, continue processing, and then issue a WAIT TERMINAL command at the point where you need to know the results of your SEND.

When you issue a RECEIVE command that requires transmission of input, your task always waits, because the transmission must occur before the RECEIVE can be completed. However, there are cases where a RECEIVE does not correspond to terminal input/output. The first RECEIVE in a task initiated by unsolicited terminal input is the most frequent example of this, but there are others, as explained in the next section.

Also, when you issue any command involving your terminal, CICS ensures that the previous command is complete (this includes any deferred transmissions), before processing the new one.