Signal handler blocks proteced type

Signal handler blocks proteced type

[Lutz Donnerhacke]

The following test program shows a strange behavior:

A protected type with a signal handler is instantiated in order to catch a
signal. If the signal is not catched, everything works fine. If the signal
was delivered, the inner scope will not be terminated, because the protected
type can not be finalized.

Why?




\f
with Ada.Text_IO;  use Ada.Text_IO;
with Ints;

procedure t is
begin
   Put_Line("Enviroment started.");
   declare
      i : Ints.Int;
   begin
      Put_Line("Waiting.");
      delay 2.0;
      if i.Found then
         Put_Line("Catched.");
      else
         Put_Line("Nothing.");
      end if;
   end;
   Put_Line("Enviroment stopped.");
end t;
\f
Example:
$ ./t
Enviroment started.
Waiting.
Nothing.
Enviroment stopped.

$ ./t & sleep 1; kill -1 %1; sleep 3
[1] 2366
Enviroment started.
Waiting.
Catched.
$ jobs
[1]+  Running                 ./t &

\f
with Ada.Interrupts.Names;   use Ada.Interrupts.Names;

package Ints is
   protected type Int is
      procedure Signal;
      pragma Attach_Handler(Signal, SIGHUP);
      procedure Reset;
      function Found return Boolean;
   private
      catched : Boolean := False;
   end Int;
end Ints;
\f
package body Ints is
   protected body Int is
      procedure Signal is
      begin
	 catched := True;   
      end Signal;
      
      procedure Reset is
      begin
	 catched := False;   
      end Reset;
      
      function Found return Boolean is
      begin
	 return catched;   
      end Found;
   end Int;
end Ints;

Signal handler blocks proteced type

[Lutz Donnerhacke]

The following test program shows a strange behavior:

A protected type with a signal handler is instantiated in order to catch a
signal. If the signal is not catched, everything works fine. If the signal
was delivered, the inner scope will not be terminated, because the protected
type can not be finalized.

Why?

Ok, there is a zombie afterwards.
\f
with Ada.Text_IO;  use Ada.Text_IO;
with Ints;

procedure t is
begin
   Put_Line("Enviroment started.");
   declare
      i : Ints.Int;
   begin
      Put_Line("Waiting.");
      delay 2.0;
      if i.Found then
         Put_Line("Catched.");
      else
         Put_Line("Nothing.");
      end if;
   end;
   Put_Line("Enviroment stopped.");
end t;
\f
Example:
$ ./t
Enviroment started.
Waiting.
Nothing.
Enviroment stopped.

$ ./t & sleep 1; kill -1 %1; sleep 3
[1] 2366
Enviroment started.
Waiting.
Catched.
$ jobs
[1]+  Running                 ./t &
$ pstree
     |-sh-+-pstree
     |    `-t---(t)

\f
with Ada.Interrupts.Names;   use Ada.Interrupts.Names;

package Ints is
   protected type Int is
      procedure Signal;
      pragma Attach_Handler(Signal, SIGHUP);
      procedure Reset;
      function Found return Boolean;
   private
      catched : Boolean := False;
   end Int;
end Ints;
\f
package body Ints is
   protected body Int is
      procedure Signal is
      begin
	 catched := True;   
      end Signal;
      
      procedure Reset is
      begin
	 catched := False;   
      end Reset;
      
      function Found return Boolean is
      begin
	 return catched;   
      end Found;
   end Int;
end Ints;

Re: Signal handler blocks proteced type

[Lutz Donnerhacke]

* Lutz Donnerhacke wrote:
> A protected type with a signal handler is instantiated in order to catch a
> signal. If the signal is not catched, everything works fine. If the signal
> was delivered, the inner scope will not be terminated, because the protected
> type can not be finalized.
>
> Why?

Ada.Interrupts.Detach_Handler is broken. It does not return if the signal
was delivered.

Changing the example to 'pragma Interrupt_Handler' and an explicit
Attach_Handler works fine (termination of the enviroment task succeeds).

Any call to Detach_Handler after a signal delivery results in a blocking
runtime call.

 select
    delay 2.0;
 else abort
    Detach_Handler(SIGHUP);
 end select;

does not work. Even an Abort_Task call from an other task has no effect.

The runtime (Linux-Threads) seems to miss an SIGCHILD and waits forever for
the wrong clone.

Re: Signal handler blocks proteced type

[Florian Weimer]

Lutz Donnerhacke <lutz@iks-jena.de> writes:

> The runtime (Linux-Threads) seems to miss an SIGCHILD and waits
> forever for the wrong clone.

I can't reproduce it on Debian/unstable (GCC 3.3.3, GNU libc 2.3.2,
Linux 2.6.4).

-- 
Current mail filters: many dial-up/DSL/cable modem hosts, and the
following domains: postino.it, tiscali.co.uk, tiscali.cz, tiscali.it,
voila.fr.

Re: Signal handler blocks proteced type

[Simon Wright]

Florian Weimer <fw@deneb.enyo.de> writes:

> I can't reproduce it on Debian/unstable (GCC 3.3.3, GNU libc 2.3.2,
> Linux 2.6.4).

Still present on a home-compiled 5.02a.

Re: Signal handler blocks proteced type

[Florian Weimer]

Simon Wright <simon@pushface.org> writes:

> Florian Weimer <fw@deneb.enyo.de> writes:
> 
> > I can't reproduce it on Debian/unstable (GCC 3.3.3, GNU libc 2.3.2,
> > Linux 2.6.4).
> 
> Still present on a home-compiled 5.02a.

It probably depends on the underlying threading implementation.  Which
one are you using?

-- 
Current mail filters: many dial-up/DSL/cable modem hosts, and the
following domains: postino.it, tiscali.co.uk, tiscali.cz, tiscali.it,
voila.fr.

Re: Signal handler blocks proteced type

[Simon Wright]

Florian Weimer <fw@deneb.enyo.de> writes:

> Simon Wright <simon@pushface.org> writes:
> 
> > Florian Weimer <fw@deneb.enyo.de> writes:
> > 
> > > I can't reproduce it on Debian/unstable (GCC 3.3.3, GNU libc 2.3.2,
> > > Linux 2.6.4).
> > 
> > Still present on a home-compiled 5.02a.
> 
> It probably depends on the underlying threading implementation.
> Which one are you using?

Whatever comes with a stock Intel Mandrake 8.2! (ie, not the new one).

-- 
Simon Wright                               100% Ada, no bugs.