HP 3000 Manuals HP 3000 Manuals
NOWAIT I/O Intrinsics To perform a NOWAIT I/O, the FREAD or FWRITE intrinsic must be called to initiate the transfer. These intrinsics return immediately, and no data is transferred yet. The return value for FREAD is set to zero and is not needed. To complete the transfer, either IODONTWAIT or IOWAIT must be called. IODONTWAIT tests whether the I/O has finished. If it has, the intrinsic returns a condition code of CCE and the file number as the return value. If the I/O has not completed, CCE and a zero return value are passed back. If IOWAIT is called, it waits until the I/O has finished, like a normal WAIT I/O FREAD or FWRITE. Only one NOWAIT I/O can be outstanding against a file by a particular accessor at a time; however, an accessor can have NOWAIT I/Os outstanding against several files at the same time. These I/Os can be completed by a "generalized" IODONTWAIT or IOWAIT (the file number parameter is zero or is omitted). In this case, these intrinsics report on the first I/O to complete, returning the file number for that file. If the call to one of these intrinsics is in a loop, then that one call can be used to complete all the NOWAIT I/Os.