Re: Ada Protected Object Tutorial #1

[Laurent Guerby <guerby@acm.org>]

kaz@ashi.footprints.net (Kaz Kylheku) writes:
> That's good. I follow the same principles generally, but without
> language help it's easy to make mistakes like do some blocking
> thing inside a tight critical section or create deadlock.

Agreed.

> What do you do if you need a protected procedure to call out into
> some other module which then calls back? 

You wouldn't do this inside the protected procedure code.

> Using explicit locks, I just unlock, do the call, lock again
> thereby avoiding deadlock.

That's how you would do it in Ada too (with an explicit mutex and
caller care). The protected objects aren't designed to solve this kind
of problem, they solve cleany most of the cases, if you have a complex
nested locks scheme, you have to do it by hand (note that the GNAT
runtime just does this, it has a very fine grained locking model by
default to allow concurrency inside itself).

> Though I don't use Ada, I have a hard copy of the standard somewhere under my
> desk, so I can take a look.

Or online: <http://www.adahome.com/rm95/>

You can get the annotated version (giving the insight on
the language design) in ASCII at 

<http://www.adaic.org/standards/95lrm/LRMascii/aarm.txt>

(There is also a PostScript version, beware it's 800 pages ;-).

--LG