[GAP] Asynchroneus IO on Mac OS X

[Christfried Webers]

While porting an Ada program running on Solaris and Linux to Mac OS X,
I ran into the problem that I could not catch SIGIO signals via an 
installed signal handler (protected procedure). Before joining the GAP, I 
filed a report to ACT ([F411-002 public], see below), but as a public 
member I had no way of figuring out what happened with it.

Therefore, I am still puzzled, whether there is any proper Ada way of 
catching the SIGIO on Mac OS X?

As mentioned below, installing a handler via a C library call to 
sigaction() can solve the problem but completely by-passes the Ada runtime 
and that just doesn't feel right.

Best
Chris

P.S.: My question has some relation to the previous thread:
I choose asynchronous IO with signals in order to be able to properly 
release (but not kill!) the reading task after a timeout if NO data is 
coming in. With blocking IO, one just hangs on the IO call.

-------------  excerpt of [F411-002 public]  -------------------------

1.) It seems that pragma Attach_Handler does not
result in a SIGIO being caught. It works fine with
other signals though. (Installing a signal handler
for the signal via a C call to sigaction() from the
Ada main program installs a handler which catches
the SIGIO signal.)

I tested it via repeated
kill -s IO   <process id>
kill -s USR1 <process id>

and only got
Got SIGUSR1, Counter =  1
Got SIGUSR1, Counter =  2
Got SIGUSR1, Counter =  3
...

------------------------------------
with Ada.Text_IO;
with Ada.Interrupts.Names;
with Signals;

procedure Demo is
   use Ada.Text_IO;
   use Ada.Interrupts;
   use Ada.Interrupts.Names;

   SIGIO_Name    : aliased String := "SIGIO";
   SIGIO_Monitor : Signals.Monitor(SIGIO, SIGIO_Name'Access);

   SIGUSR1_Name    : aliased String := "SIGUSR1";
   SIGUSR1_Monitor : Signals.Monitor(SIGUSR1, SIGUSR1_Name'Access);

begin
   loop
      delay 1.0;
   end loop;
end Demo;

package Signals is
   use  Ada.Interrupts, Ada.Interrupts.Names;

   --  Must first unreserve this interrupt if using SIGINT
   pragma Unreserve_All_Interrupts;

   protected type Monitor (Signal : Interrupt_ID;
                           Name   : access String) is
      procedure Handler;
      pragma Attach_Handler (Handler, Signal);
   private
      Counter : Natural := 0;
   end Monitor;
end Signals;

with Ada.Text_IO;

package body Signals is
   use Ada.Text_IO;

   protected body Monitor is
      procedure Handler is
      begin
         Counter := Counter + 1;
         Put_Line ("Got " & Name.all &
                   ", Counter = " & Counter'Img);
      end Handler;
   end Monitor;
end Signals;
----------------------------------------------------------------------

Christfried Webers                     Department of Information Engineering
Ph  +61 2 6125 8602    Research School of Information Sciences & Engineering
Fax +61 2 6125 8660                    and    Department of Computer Science
Christfried.Webers at anu.edu.au          Australian National University