[Info-vax] QIO Writes to a mailbox

[Bob Koehler]

In article <4eb4b83a$0$8581$c3e8da3$cc4fe22d at news.astraweb.com>, JF Mezei <jfmezei.spamnot at vaxination.ca> writes:
> Johnny Billquist wrote:
> 
>> No. This is not correct. QIO, as well as QIOW will not copy the data 
>> before returning from the system call. 
> 
> QIOW by definition waits for an event flag to be set to signal that the
> IO has completed, so this garantees that the buffer has not only been
> copied, but also been written in full to the mailbox device.

   Actually, since $SYNCH was introduced, $QIOW call $SYNCH, which
   checks both that the EFN is set and that the IOSB has data in it.