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Date: 22 Apr 92 12:03:24 GMT
From: deccrl!news.crl.dec.com!hollie.rdg.dec.com!player.enet.dec.com!vanavermae
t@decwrl.dec.com
Subject: Re: Ada multitasking with X-windows
Message-ID: <1992Apr22.120324.25615@rdg.dec.com>
List-Id: <comp.lang.ada>

with standard_disclaimer; use standard_disclaimer;

I think a number of issues have been confused in the heated discussion that
followed.

The first issue was that X and Xt are not thread-safe - you have to make all
calls from one task.

The same is probably true for (the implementation of) SQL (but I do not think
that any particular SQL implementation was ever mentioned).

Another (potential) problem that was not mentioned is that it might be a bit
difficult to reconcile XtMainLoop with Ada tasking - but I have no experience
with this.

An issue that WAS mentioned, is that the developer wanted the X application to
continue to function while the SQL operation was in progress. The problem there
would be, that when a software layer (e.g., an SQL implementation) blocks a
task, it might block the whole process (it depends, I suppose, on that software
layer, on your operating system, and on the implemntation of the Ada run-time
system).

Some people have suggested separating this into 2 processes - I would agree. Th
e
client would do the X stuff, and the server would do the SQL stuff. They could
communicate through a pair of pipes (Unix) or a pair of mailboxes (VAX/VMS). Yo
u
would have to prevent the client from blocking (the whole process) while
performing operations on those pipes/mailboxes - but that should not be too
difficult. This solution would not be identical for the different platforms (th
e
author of the original note did not mention which platforms he had in mind), bu
t
it would be similar - and the differences could probably be confined to a coupl
e
of package bodies.