The CHECK TERMINAL statement tests whether a previously issued asynchronous I/O operation is complete. If a READ TERMINAL, WRITE TERMINAL, or WRITE THEN READ TERMINAL request specifies the NOWAIT option, the program must issue a CHECK TERMINAL request before specifying any other I/O operation. If the I/O operation is not complete, the system suspends task execution. When the I/O operation is complete, the task resumes execution according to its established dispatching priority.
►►─── CHECK TERMINAL; ────────────────────────────────────────────────────────►◄
Upon completion of the CHECK TERMINAL function, the ERROR_STATUS field in the IDMS DC communications block indicates the outcome of the operation:
The request has been serviced successfully.
The input area specified for the return of data is too small; the returned data has been truncated to fit the available space.
The output operation has been interrupted; the terminal operator has pressed ATTENTION or BREAK.
A logical error (for example, an invalid control character) has been encountered in the output data stream.
A permanent I/O error has occurred during processing.
The dial-up line for the terminal being used has been disconnected.
The terminal request block (TRB) contains an invalid field, indicating a possible error in the program's parameters.
The terminal device associated with the issuing task is out of service.
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