Re: Structure of the multitasking server

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

On Sun, 21 Sep 2008 10:30:37 -0700 (PDT), Maciej Sobczak wrote:

> On 19 Wrz, 19:02, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
> 
>> Note that task termination is usually a difficult problem in Ada. You
>> should pay an attention to this early.
> 
> No problem with that. With separate protected object (instead of
> rendezvous) it is enough to do this:

Of course there is a problem because conditional and timed entry calls may
not contain a "terminate" alternative. This is another reason why a
protected object might be a poor choice. But the way you used protected
object looks like a design noise. Technically you just replaced a
rendezvous queue with a protected entry queue. Instead of just server and
workers, you have server, workers, channels and management stuff. Very
OO-ish in the negative sense of this word.

The second problem which adds complexity is server to worker 1-n
communication. Should be n-1 worker to server, simpler (classic
client-server) and more efficient too.

Due to complexity you have overlooked to make a channel idle again after a
job is done. You also have overlooked to add a "Shut_Down" state in order
to finalize workers: four channel states instead of just none. And note,
that the type Channel cannot call to the procedure Finish to set Shut_Down
from its Finalize (if it were controlled). That is because Worker is a
component of. The thing will hang up on channel destruction. 

> There is no need to introduce any special type of job ("poison pill").

Job carries the parameters of a worker. You used it too, under the name
Job_Type.

> Above, the job space is not polluted with task lifetime management
> concepts - these should be kept separate.

You have polluted it with the procedure Finish, that has to be called
outside the worker tasks.

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