Re: ASYN - weird

[Andrew Johnson <anj@aps.anl.gov>]

Heinrich du Toit wrote:
> Why is CreateUser called twice with different asynUser's ??
>
> I've seen this dual-called behaviour of DrvUser before in my other
> drivers. This time I would like to figure it out :)

An asynUser is a structure that Asyn uses to hold information about an 
individual I/O transaction (the name is unfortunate, it's not very 
descriptive of what it really does).  Asyn needs one of these for each 
independent transaction that could conceivably be active at once â 
typically that will be one or possibly two per record as Mark Rivers 
described, but that choice is completely up to whatever is connecting to 
the port.  Your port code should be written to accept any number of 
asynUser objects presented to it; the Asyn code provides the locking and 
queuing that ensures only one of them can be active at any time.

- Andrew
--
When a distinguished but elderly scientist states that something is
possible, he is almost certainly right.  When he states that something
is impossible, he is very probably wrong.  -- Arthur C. Clarke