[Info-vax] QIO Writes to a mailbox

[JF Mezei]

Michael Moroney wrote:

> Not checking the status is almost certainly the cause of the problem.


I disagree. It is not the *cause* of the problem. It merely means that
the aplication won't detect a problem and attempt to correct it.

Furthermore, it is entirely possible that the sending application has
succesfully written to the mailbox device and the message gets lost
later. In such a scenario, the sending application would see a succesful
IO completion in the IOSB but would not know that the intended
application did not read that message, or read it and discarded it.

Since a write to a mailbox is nearly instantaneous if here is sufficient
buffer space to add the new message, the use of QIO or QIOW doesn't make
much of a difference from a timing point of view. They either work right
away or cause the process to get hung in RWMBX until someone reads from
the mailbox.