Printer file considerations for multithreaded programming
Only printer files opened with SPOOL(*YES) are allowed in a job that is capable of multithread operations.
Unspooled opens of printer files fail with a CPF4380 (Open attributes not valid in a multithreaded process) escape message sent to the function that requested the open.
Most SNA character string (SCS), Intelligent Printer Data Stream (IPDS), Advanced Function Printing data stream (AFPDS), LINE, and USERASCII write operations are threadsafe. Write operations that are not threadsafe include those that use SCS graphics, those that the System/36 Environment uses, those generated by the User Interface Manager (UIM), and those that use System/36 PRPQ subroutines. Page and line counts might be inaccurate because those counters cannot be atomically updated.