Re: To raise an exception in task and handle/catch it in outer-block.

[Craig Carey <research@ijs.co.nz>]

On Sun, 4 Jan 2004 12:58:52 -0800, "Frank" <franjoe@frisurf.no> wrote:
...
>This issue came up because a exception raised in a task like this is not
>propagated automatically by Ada to the outer block, but is resolved within
>each task.
...
>   task body A_Task is
...
>   exception
>      when others =>
>        begin
>          accept Stop do -- ... as in example
>
>          accept Final do -- repeated here for clarity
>            Ada.Text_IO.Put_Line ("Test_Task_Exception.A_Task.Final...
>               -- We wish to communicate exception to the outer-block

>            raise test_exception;    <<<=== Bad News here. Delete this !!

>          end Final;
>        end;
>   end A_Task;
>end Test_Task_Exception;


Lockups in GNAT running in Linux were observed by me to occur in Linux
 when an exception was raised in a task's outmost exception handler.

The debugger may be unhelpful so it may be best to check all code and
delete any that would allow a task to be exited by the raising of an
exception.

Deleting that "raise" statement still leaves the Put_Line line which 
could also raise an exception.

The lockup problems maybe are absent in Windows. In Linux, a call to
C's exit() [GNAT's OS_Exit] can zombi-ize the program over delay
statements, and any sort of blocking (though I don't recall seeing
barriers of protected objects being implication in the construction of
zombies).

The above call to raise is a way to get a lockup without any blocking.
I never submitted a bug report.


Craig Carey