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From: "fabio de francesco" <fmdf@tiscali.it>
Newsgroups: comp.lang.ada
Subject: [newbie question] tasks and protected types
Date: 28 Apr 2005 21:04:17 -0700
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Date: 2005-04-28T21:04:17-07:00
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Hello,

It's the first time I have something to do with protected types and
tasks, so please forgive this newbie question.

The problem is that I have the following program that compiles without
errors but that must have some logical errors. When it is run, it hangs
endlessy. I have only copied the relevant part omitting what is
unneeded to this discussion, anyway it can be compiled without syntax
errors.

First please let me explain what I wanted it to do. I want two
concurrent tasks to get some numbered "tickets" at random intervals.
Each different "ticket" number must be given to each task without
duplication. Every time a task is provided with "ticket" the name of
the task itself and the number is showed. This is like a bank with two
doors assigning numbered tickets to entering customers in order to be
later served at the counter by showing tickets representing order of
arrival.

So I wanted to create two tasks (D1, D2) that wait to be activated with
"Start()". Each of them ask the protected object for a number at random
intervals and then show it with "Put()".

I am not even sure if it is the correct logical implementation. Please,
let me know what I am missing. I apologize you all if my poor English
prevented proper explanation of this issue.

Regards,

fmdf


-- manage.adb

with Ada.Text_IO, Ada.Numerics.Float_Random;
use Ada.Text_IO, Ada.Numerics.Float_Random;

procedure Manage is

    protected Tickets is
        procedure Assign(New_Value: out Positive);
    private
            Data: Integer := 0;
    end Tickets;

    protected body Tickets is
        procedure Assign(New_Value: out Positive) is
        begin
            Data := Data + 1;
            New_Value := Data;
        end Assign;
    end Tickets;

    G : Generator;

    task type Door is
        entry Start( Str : in String; Tm : in Positive );
    end Door;

    task body Door is
        Msg : String := "";
        Val : Positive;
        Times : Positive;
    begin
        accept Start( Str : in String; Tm : in Positive ) do
            Msg := Str;
            Times := Tm;
        end Start;
        for I in 1..Times loop
            delay( Duration( Random( G ) ) );
            Tickets.Assign( Val );
            Put( Msg & " counts " & Natural'Image( Val ) );
            Flush;
        end loop;
    end Door;

    D1 : Door;
    D2 : Door;

begin

    Reset( G );
    D1.Start( "Task 1", 6 );
    D2.Start( "Task 2", 6 );
    
end Manage;