Each User Logging intrinsic includes a mode parameter used
to indicate whether the I/O is to be performed with WAIT
or NOWAIT. If NOWAIT is specified and the User Logging
process is busy with a long operation (for example, allocation of
disc space or writing a block to tape, etc.) and cannot accept
data, an error will be returned and the operation should be
attempted again.
If WAIT is specified and the User Logging process is busy,
the intrinsic will return to its caller only after the User
Logging process becomes available and the I/O completes.
WRITELOG allows a third value for the mode parameter,
WRITE-and-FLUSH, which causes the User Logging buffer
to be flushed at the first opportunity.
