[Info-vax] QIO Writes to a mailbox

[Christoph Gartmann]

In article <e519cbe4-54bc-480c-8b07-267b9f90edda at q13g2000vbd.googlegroups.com>, Steve Bainbridge <stephen_bainbridge at yahoo.co.uk> writes:

>We have some old code that issues a QIO WRITEVBLK to a mailbox - the
>return code from the QIO is normal. Another process reads the mailbox
>and never gets the message - this only happens very rarely.
>Unfortunately the writer does not check or report what value the IOSB
>returns and I need to try and understand why these messages are
>getting lost. I can't reproduce this on our test systems and I can't
>easily install updated diagnostic code onto these production systems.
>
>The question I have is when is the data pointed to by P1 (in the QIO
>call) actually copied ? It is always done within the QIO routine or is
>it just scheduled to be done in the QIO call ? Can I re-use the buffer
>pointed to by P1 immediately after the call to the QIO ?

Is it QIO or QIOW? The former is asynchronous, that is, the program continues
and doesn't wait for the function to complete. This would explain your
problems.

Regards,
   Christoph Gartmann

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