[Info-vax] QIO Writes to a mailbox

[VAXman- at SendSpamHere.ORG]

In article <j9c6ug$r1s$1 at news.albasani.net>, Jan-Erik Soderholm <jan-erik.soderholm at telia.com> writes:
>JF Mezei wrote 2011-11-08 20:12:
>> VAXman- @SendSpamHere.ORG wrote:
>>
>>> Specify the IOSB, check it and assume nothing!  Then, the code should
>>> work.
>>
>> No. Looking at the IOSB won't make the code work and the problem
>> disappear. You will just notice a bad retrun code should there be one.
>>
>> However, the writing process may be working fine and it may be the
>> reading process which dicards a message by mistake.
>>
>> While it is not kosher for the writng process do to a $QIO without
>> waiting for completion and checking the IOSB to at least report a
>> problem in a log, this may not be the cause of the problem. It just
>> allows the problem to go undetected by the writing process IF the
>> problem is with the writing process.
>>
>> Note that if the writing process excepts an answer from the other
>> process, there may be a wait statement there (waiting for the answer)
>> which does imply that the writing process will wait for the $QIO to
>> complete before issuing the next one.
>
>Now, if you want to do a $QIO and then always *wait* for completion,
>why not use $QIOW in the first place ?
>
>One efficient way to do it is to check the previous IO (say, by
>checking the IOSB) right *before* you will do the *next* $QIO.
>In that way, you can do any other processing you like in your
>app while the I/O subsystem completes the IO asyncronicaly.
>
>Always waiting right *after* the $QIO is inefficent and you could
>anyway use $QIOW and let the system take care of the "waiting".

Even when using $QIO and an AST, one needs to check the IOSB.  Like I said,
specify the IOSB, check it and assume nothing!

-- 
VAXman- A Bored Certified VMS Kernel Mode Hacker    VAXman(at)TMESIS(dot)ORG

All your spirit rack abuses, come to haunt you back by day.
All your Byzantine excuses, given time, given you away.