[Info-vax] QIO Writes to a mailbox

[Michael Moroney]

JF Mezei <jfmezei.spamnot at vaxination.ca> writes:

>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.

...

>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.

Not true, unless IO$M_NOW was specified on the write.  Otherwise, the 
write QIO(W) won't complete until another process issues a read, and that
could be a *significant* delay, if the reader was delayed.

I don't remember from the source supplied whether IO$M_NOW was actually
specified.