global rendezvou's

global rendezvou's

[kumkwat]

HI

I was wondering if it was possible to have a entry call in a task that
was not only defined in multiple tasks but because it is then I
wouldn't have to specify the name of the task first before calling the
entry.  Basically I don't want to call the entry on a specific task but
just tell everyone that I want to pass an object to the first thread
that calls an accept.  I've got a way via a protected object as a
buffer but was wondering if I could circumvent that and just do it this
way.

e.g

task temp1 is
   entry hello;
end temp1;

task temp2 is
   entry hello;
end temp2;


-- somewhere in the main thread
hello;

-- and not temp1.hello; or temp2.hello;

Thanks
Jason


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Re: global rendezvou's

[Matthew Heaney]

kumkwat@my-dejanews.com writes:

> I was wondering if it was possible to have a entry call in a task that
> was not only defined in multiple tasks but because it is then I
> wouldn't have to specify the name of the task first before calling the
> entry.  Basically I don't want to call the entry on a specific task but
> just tell everyone that I want to pass an object to the first thread
> that calls an accept.  I've got a way via a protected object as a
> buffer but was wondering if I could circumvent that and just do it this
> way.

If you want a broadcast feature, then you need to use a protected object
to implement a signal.

There are many examples of this in the ACM patterns archive; see the
dining philosophers series of articles.

<http://www.acm.org/archives/patterns.html>

 
> task temp1 is
>    entry hello;
> end temp1;
> 
> task temp2 is
>    entry hello;
> end temp2;
> 
> 
> -- somewhere in the main thread
> hello;
> 
> -- and not temp1.hello; or temp2.hello;


You sound like you know this, but here it goes:

  protected Task_Initialization is

    procedure Start;

    entry Wait;

  private

    Started : Boolean := False;

  end;

  protected body Task_Initialization is

    procedure Start is
    begin
      Started := True;
    end;

    entry Wait when Started is
    begin
      null;
    end;

  end;


  task body Temp1 is
  begin

    Task_Initialization.Wait;

    ...

  end;


  task body Temp2 is
  begin

    Task_Initialization.Wait;

    ...

  end;
 

Re: global rendezvou's

[Nick Roberts]

And if anyone is wondering why Ada is designed this way, it is (someone
correct me if I'm wrong) to do with implementation: the Ada rendezvous
mechanism (wherein the recipient is always specified by the sender) makes
for a particularly simple implementation, not requiring any chunks of memory
to be allocated for queue space (queues of waiting callers are simply
implemented by a having a 'waiting-link-through' pointer in each task's
descriptor).

-------------------------------------
Nick Roberts
http://www.adapower.com/lab/adaos
-------------------------------------