Re: Random numbers in tasks

["Papastefanos Serafeim" <serafeim@otenet.gr>]

Thank you for the big answer... I tried your program and
it works just fine, but when I try to convert it to my
requirements it is not working:
I want to use it with discrete rundom numbers with a
variable range... I have made changes to your program
and now looks like this ->
with Ada.Numerics.Discrete_Random;
with Ada.Task_Attributes;
package body Rnds is
   function Give_Rnd (
         L : Integer;
         U : Integer;
)      return Integer is
      subtype Rng is Integer range L..U;
      package Rnd_Num is new Ada.Numerics.Discrete_Random (Rng);
      type Generator_Pointer is access Rnd_Num.Generator;
      protected Gen_Source is
         procedure Initialize_Generator (
               Pointer : in out Generator_Pointer );
      private
         Init: Integer := 10;
      end Gen_Source;

      protected body Gen_Source is
         procedure Initialize_Generator (
               Pointer : in out Generator_Pointer ) is
         begin
            Pointer := new Rnd_Num.Generator;
            Rnd_Num.Reset(Pointer.All, Init);
            Init := Init + 10;
         end Initialize_Generator;
      end Gen_Source;

      function Initialize return Generator_Pointer is
         Gp : Generator_Pointer;
      begin
         Gen_Source.Initialize_Generator(Gp);
         return Gp;
      end Initialize;
      package Per_Task is new
         Ada.Task_Attributes(Generator_Pointer, Initialize);

   begin
      return Rnd_Num.Random(Per_Task.Value.All);
   end Give_Rnd;
end Rnds;

It compiles fine but when I try to call the function Give_Rnd(...)
from inside a task it always returns the same result - Am I doing
something wrong ?



"Robert I. Eachus" <rieachus@attbi.com> wrote in message
news:3EDAC482.40604@attbi.com...
> Papastefanos Serafeim wrote:
> > There is a small problem in that solution, I cannot just
> > declare the generator in the task type: There is a function in
> > a different package that is used to return a random
> > number in a given range and that function is used at
> > other places too...
>
> There is magic in Ada for especially this purpose.  It is in Annex C, so
> it is possible that some compilers don't support it.  Look at C.7.2 The
> Package Task_Attributes.  Here is an example and output using GNAT.
> Notice that this version uses a fixed seed for each different task.  If
> you want different seeds for every run modify the body of
> My_Float_Random.Gen_Source.  But notice that just using a call to get
> seeds based on the clock may not be sufficient, unless you put a delay in.
>
> with Ada.Task_Attributes;
> with Ada.Numerics.Float_Random;
> package My_Float_Random is
>    function Random return Ada.Numerics.Float_Random.Uniformly_Distributed;
> end My_Float_Random;
>
> package body My_Float_Random is
>     type Generator_Pointer is access Ada.Numerics.Float_Random.Generator;
>
>     protected Gen_Source is
>       procedure Initialize_Generator(Pointer: in out Generator_Pointer);
>     private
>       Init: Integer := 10;
>     end Gen_Source;
>
>     protected body Gen_Source is
>       procedure Initialize_Generator
>                   (Pointer: in out Generator_Pointer) is
>        begin
>          Pointer := new Ada.Numerics.Float_Random.Generator;
>          Ada.Numerics.Float_Random.Reset(Pointer.all, Init);
>          Init := Init + 10;
>        end  Initialize_Generator;
>
>     end Gen_Source;
>
>     function Initialize return Generator_Pointer is
>       GP : Generator_Pointer;
>     begin
>       Gen_Source.Initialize_Generator(GP);
>       return GP;
>     end Initialize;
>
>     package Per_Task is new
>       Ada.Task_Attributes(Generator_Pointer, Initialize);
>
>     function Random return
>        Ada.Numerics.Float_Random.Uniformly_Distributed is
>     begin
>       return Ada.Numerics.Float_Random.Random(Per_Task.Value.all);
>     end Random;
>
> end My_Float_Random;
>
> with Ada.Text_IO;
> with My_Float_Random;
> procedure Test_Task_Random is
>
>     package Rand_IO is new Ada.Text_IO.Float_IO(Float);
>
>     task type Rand_Task (ID: Integer) is end Rand_Task;
>
>     type Task_Pointer is access Rand_Task;
>     TP : Task_Pointer;
>
>     protected IO_Serialize is
>       procedure Write_Line(S: in String);
>     end IO_Serialize;
>
>     protected body IO_Serialize is
>       procedure Write_Line (S: in String)
>       is begin Ada.Text_IO.Put_Line(S); end Write_Line;
>     end IO_Serialize;
>
>     task body Rand_Task is
>       Rand_String: String(1..10);
>     begin
>       for I in 1..10 loop
>         Rand_IO.Put(Rand_String, My_Float_Random.Random, 7, 0);
>         IO_Serialize.Write_Line( "Task" & Integer'Image(ID) &
>            " Random number: " & Rand_String);
>       end loop;
>     end Rand_Task;
>
> begin
>
>     for I in 1..10 loop
>       TP := new Rand_Task(I);
>     end loop;
>
> end Test_Task_Random;
>
> E:\Ada\Random>test_task_random
> test_task_random
> Task 1 Random number:  0.7443592
> Task 1 Random number:  0.1400007
> Task 1 Random number:  0.9659407
> Task 1 Random number:  0.6070659
> ...
> Task 6 Random number:  0.3006703
> Task 7 Random number:  0.5094006
> Task 8 Random number:  0.9858680
> Task 10 Random number:  0.2958182
> Task 9 Random number:  0.7662218
> Task 10 Random number:  0.4117813
> Task 9 Random number:  0.9709954
> Task 10 Random number:  0.2093689
> Task 9 Random number:  0.3808535
> Task 10 Random number:  0.6235309
>
>
>
>
>