Object-oriented Software in Ada 95

296 Tasks
A package Pack_types is defined to allow commonly-used types to be conveniently kept together.
with Ada.Text_Io;
use Ada.Text_Io;
package Pack_Types is
type P_File_Type is access all Ada.Text_Io.File_Type;
Eot : constant Character := Character'Val(0);
Cr : constant Character := Character'Val(15);
Queue_Size : constant := 3;
type Queue_No is new Integer range 0 .. Queue_Size;
type Queue_Index is mod Queue_Size;
subtype Queue_Range is Queue_Index;
type Queue_Array is array ( Queue_Range ) of Character;
end Pack_Types;
Note:
The above package is used to define the type P_File_Type which is used by several other program
units.
The specification for the buffer protected type is as follows:
with Pack_Types;
use Pack_Types;
package Pack_Threads is
protected type PT_Buffer is --Task type specification
entry Put( Ch:in Character; No_More:in Boolean );
entry Get( Ch:in out Character; No_More:out Boolean);
private
Elements : Queue_Array; --Array of elements
Head : Queue_Index := 0; --Index
Tail : Queue_Index := 0; --Index
No_In_Queue : Queue_No := 0; --Number in queue
Fin : Boolean := False; --Finish;
end PT_Buffer ;
type P_PT_Buffer is access all PT_Buffer ;
The Ada specification for the reader and writer tasks are as follows:
task type Task_Read( P_Buffer:P_PT_Buffer ;
Fd_In:P_File_Type) is
entry Finish;
end Task_Read;
task type Task_Write( P_Buffer:P_PT_Buffer ;
Fd_Out:P_File_Type) is
entry Finish;
end Task_Write;
end Pack_Threads;
Note:
To allow the reader and writer tasks to communicate with the buffer, a reference to the buffer protected
object is passed to these tasks. A reference to the buffer protected object has to be passed as a
protected object is of limited type.
The same strategy is used to pass an instance of File_Type.
© M A Smith - May not be reproduced without permission