Open System Services Programmer's Guide

OSS files can also be managed from the Guardian API. You would use Guardian procedures to
access OSS files when you need to perform operations that use the nowait feature of the Guardian
environment.
Nowait I/O is the ability of an application process to continue executing in parallel with read and
write operations; the application process runs concurrently with the I/O operation. The OSS
environment uses waited I/O, where an application process is suspended during read and write
operations. The process does not resume execution until the I/O operations are complete. Nowait
I/O does not work on files that have been opened with the OSS open() function.
When you use a Guardian I/O procedure in nowait mode, you set the maximum number of
concurrent I/O operations that you want to allow and then complete the I/O operations by calling
the AWAITIO[X] procedure later in your program, as shown in Example 21 (page 71). For details
on using nowait I/O with Guardian procedures, refer to the Guardian Programmer’s Guide.
Accessing Files From the Guardian API 69