[Info-vax] QIO Writes to a mailbox

[VAXman- at SendSpamHere.ORG]

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, it does in implicit $SYNCH.  It waits using both the EFN and
the IOSB.  With the advent of threading, using an event flag can cause
the program to misbehave because event flags are not thread specific.
The ENF (event no flag) event flag was created for this case but one
still needs to check the IOSB.  Hopefully, if you are programming with
threads, you're smart enough to realize you'll need NON-SHARED IOSBs!

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