阿达关机钩

Question

当Ada应用程序被关闭/终止时,我想要一些'清理'调用.

例如,如果我在java中,我会做这样的事情来达到在关机时调用的效果:

Runtime.getRuntime().addShutdownHook(new Thread(){
       public void run(){
            method();
       }
});

在Ada中有类似的东西或其他方式来实现这一目标吗？

Answer 1

由于Ada主程序被视为任务,因此您可以使用Ada.Task_Termination包来管理执行后清理.在Ada 2005 Rationale中有一篇关于此的文章,接下来是我在一个示例的基础上编写的快速演示.

您必须提供库级保护终止过程,因此这是一个包:

with Ada.Task_Termination;
with Ada.Task_Identification;
with Ada.Exceptions;

package Main_Program_Finalization is

   protected Shutdown_Handler is

      procedure Termination_Finalizer 
        (Cause : in Ada.Task_Termination.Cause_Of_Termination;
         T     : in Ada.Task_Identification.Task_Id;
         X     : in Ada.Exceptions.Exception_Occurrence);
   end Shutdown_Handler;

end Main_Program_Finalization;

身体:

with Text_IO; use Text_IO;

package body Main_Program_Finalization is

   protected body Shutdown_Handler is

      procedure Termination_Finalizer
        (Cause : in Ada.Task_Termination.Cause_Of_Termination;
         T     : in Ada.Task_Identification.Task_Id;
         X     : in Ada.Exceptions.Exception_Occurrence)
      is
         use Ada.Task_Termination;
         use Ada.Task_Identification;
         use Ada.Exceptions;
      begin
         New_Line;
         Put_Line("Shutdown information:");
         New_Line;
         case Cause is
         when Normal =>
            Put_Line("Normal, boring termination");
         when Abnormal =>
            Put_Line("Something nasty happened to task ");
            Put_Line(Image(T));
         when Unhandled_Exception =>
            Put_Line("Unhandled exception occurred in task ");
            Put_Line(Image(T));
            Put_Line(Exception_Information(X));
         end case;
      end Termination_Finalizer;

   end Shutdown_Handler;

end Main_Program_Finalization;

主程序(设置为已发布的正常终止,取消注释最后两行并运行它以查看未处理的异常触发终止的影响):

with Main_Program_Finalization;
with Ada.Task_Identification;
with Ada.Task_Termination;
with Text_IO; use Text_IO;

procedure task_term is

   use Ada;

   Task_ID : Task_Identification.Task_Id
     := Task_Identification.Current_Task;

begin
   Put_Line("Main Task ID: " & Task_Identification.Image(Task_ID));

   Put_Line("Setting termination finalizer");
   Task_Termination.Set_Specific_Handler
     (Task_ID, 
      Main_Program_Finalization.Shutdown_Handler.Termination_Finalizer'Access);
   Put_Line("Go off and do things now...");
   delay 1.0;
   Put_Line("Done with mainline processing, the shutdown handler should now execute");

--     Put_Line("Raise an unhandled exception and see what the shutdown handler does");
--     raise Constraint_Error;
end Task_Term;

Answer 2

您可以为主过程创建一个受控(或Limited_Controlled)对象,该过程在其Finalization方法中调用必要的东西.

请注意,您无法访问主过程的任何局部变量,因此请将任何必要的内容放入受控对象中.

例:

with Ada.Text_IO;
with Ada.Finalization;
procedure Main is
   type Cleaner is new Ada.Finalization.Limited_Controlled with record
      Some_Interesting_Data : Integer;
   end record;
   overriding procedure Finalize (X : in out Cleaner) is
   begin
      Ada.Text_IO.Put_Line ("Cleaning..." & Integer'Image (X.Some_Interesting_Data));
   end Finalize;
   The_Cleaner : Cleaner;
begin
   Ada.Text_IO.Put_Line ("Main Procedure.");
   The_Cleaner.Some_Interesting_Data := 42;
   Ada.Text_IO.Put_Line ("Finished.");
end Main;