Object-oriented Software in Ada 95

304 Tasks
20.8.2 As part of a program unit
package Pack_Factorial is
task type Task_Factorial(F:Positive) is --Specification
entry Finish( Result:out Positive ); --Rendezvous
end Task_Factorial;
end Pack_Factorial;
--[pack_factorial.adb] Implementation
package body Pack_Factorial is
task body Task_Factorial is --Implementation
Answer : Positive := 1;
begin
for I in 2 .. F loop
--Calculate
Answer := Answer * I;
end loop;
accept Finish( Result:out Positive ) do --Return answer
Result := Answer;
end Finish;
end Task_Factorial;
end Pack_Factorial;
with Ada.Text_Io, Ada.Integer_Text_Io, Pack_Factorial;
use Ada.Text_Io, Ada.Integer_Text_Io, Pack_Factorial;
procedure Main is
Num : Positive;
begin
Num := 7;
declare
Factorial: Positive;
Thread_1 : Task_Factorial(Num);
begin
--Do some other work as well
Put("Factorial "); Put(Num); Put(" is ");
Thread_1.Finish( Factorial );
Put( Factorial ); New_Line;
end;
--Answer
--Task is
--Obtain result
end Main;
Note:
The task will come into existence as soon as the program unit is executed.
20.9 Self-assessment
• What is a thread or task in a programming language?
• What Ada construct can be used to implement a thread or task?
• How is information passed between two threads? Explain why a special construct is required for this
activity.
• What is the difference between a task type and a normal type?
• What is the difference between execution of a procedure and execution of a function in a protected
type?
• What happens when a task type is elaborated?
© M A Smith - May not be reproduced without permission