Re: CA on VMS

[hill@luke.atdiv.lanl.gov (Jeff Hill)]

> 
> Has 3.12 CA stopped being asynchronous on VMS or am I being dumb?
> 
> I am playing around with my first VMS CA client and I understood that
> CA used AST's to handle events. That is, my understanding is that event
> handlers would execute in AST context and so a call to ca_pend_event
> was not required for an event to be processed.
> 
> However, my event handlers only appear to be executed when I call
> ca_pend_event, or some other CA routine.
> 
> I don't mind if the functionality has changed, only I wish the
> documentation would be a bit more clear.

You are correct. I dropped AST driven CA event preemption under VMS 
because the MULTINET socket library isnt reentrant and they (TGV) 
dont appear to be interested in solving the problem. I was able to 
work around  these problems in the past however it was becoming 
increasingly difficult to remain portable.

You are also correct about the documentation needing to be updated
concerning this particular point. I have updated my copy and will
place this on the WEB prior to official release of R3.12.

> 
> An alternative question is - is there a way of a particular event
> forcing ca_pend_event to return? The way I see it, it always waits at
> least for the specified interval.
> 

You need a version of ca_pend_event () that returns immediately
if any CA events are executed? We accomplish this under UNIX by
using the routines in libCom/fdmgr.c (prototypes and minimal
doc in include/fdmgr.h). Basically, we wait in the file descriptor
manager until there is activity on one of CA's file descriptors 
and then call ca_pend_event(0.00001). The file descriptor manager 
always returns immediately after handling file descriptor activity
(even if the specified delay hasnt expired). I can point you
to several short example codes if you are interested.

The file descriptor manager is implemented on top of select().
The primary purpose of the file descriptor manager is to allow
multiple libraries that use file descriptors to co-exist within
the same process. Unfortunately, the MULTINET version of select
does not work with VMS channels that are not MULTINET sockets.
This may not be the case with UCX.

It also might be possible to add a new type of ca_pend_XXXX() to the
CA API.


Jeff
______________________________________________________________________
Jeffrey O. Hill			Internet	johill@lanl.gov
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