Re: Termination of tasks waiting on a protected queue

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 19 May 2014 16:49:29 -0500, Randy Brukardt wrote:

> <sbelmont700@gmail.com> wrote in message 
> news:3ab5fcf0-d2a8-4c82-ab51-02b829aebcaa@googlegroups.com...
>> It has always seemed strange that Ada doesn't seem to have a way to block 
>> on multiple entries, in line with posix select() or waitformultipleobjects. 
>> I'd be happy with even just a function that can wait on an array of suspension objects.
> 
> There was such a proposal for Ada 9x. After much discussion, a report was 
> commissioned from the three user-implementor teams. All three reported that 
> the operation would be much more expensive to implement than it appears on 
> the surface. In particular, the people with hard real-time deadlines could 
> not use any imaginable implementation of the feature -- which would have 
> made it useless to the #1 constituency. The idea was dropped and never has 
> been raised since.

For the OP problem, which is quite common, it would be enough to allow
single terminate alternative in select. Then code could be written as:

   task body Worker is
      Job : Job_Description;
   begin
      loop
         select
            Queue.Get_Next (Job);
            -- Do the job
         or delay 1.0;
         end select;
         select   -- This is not Ada!
            terminate;
         else
            exit;
         end select;
      end loop;
   end Worker;   

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de