Missing in sigaction

27 Mar 2012

      Hi

instead of many words, here's the output of two program runs once with a sleep( 2) - as in seconds, not as in man -  commented in and out. What I believe this demonstrates, is that on Darwin (Kernel Version 10.8.0), blocked signal information is lost, which is incovenient. gdb has a similiar problem.

Or it shows that I am misunderstanding something ;)

The problem is not that the signal is occurring less often, that's expected, but that the struct __siginfo has trouble remembering things.

Ciao
   Nat!

Run #1 (without sleep(2) in signal_action)

993: sigaction
993: fork
993: fork
993: wait
994: kill
994: sleep
993: signal 30 from { 30, 0, 0, 994 }
995: kill
995: sleep
993: signal 30 from { 30, 0, 0, 995 }
994: kill
994: sleep
993: signal 30 from { 30, 0, 0, 994 }
995: kill
995: sleep
993: signal 30 from { 30, 0, 0, 995 }
994: _exit
995: _exit
993: wait
993: _exit

Run #2 (with sleep( 2) in signal_action)

973: sigaction
973: fork
973: fork
973: wait
974: kill
974: sleep
973: signal 30 from { 30, 0, 0, 974 }
973: sleep
975: kill
975: sleep
974: kill
974: sleep
975: kill
975: sleep
973: signal 30 from { 30, 0, 0, 0 }        <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
974: _exit
973: sleep
975: _exit
973: wait
973: _exit

Source code.

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void  p_log( char *s)
{
   printf( "%d: %s\n", getpid(), s);
}

static void  signal_action( int signal, struct __siginfo *info, void *data)
{
   printf( "%d: signal %d from { %d, %d, %d, %d }\n", getpid(), signal, info->si_signo, info->si_errno, info->si_code, info->si_pid);

   /// COMMENT-UNCOMMENT ///
   p_log( "sleep");
   sleep( 2);
}

static void   _test( void)
{
   p_log( "fork");
   if( ! fork())
   {
      p_log( "kill");
      kill( getppid(), SIGUSR1);
      p_log( "sleep");
      sleep( 1);
      p_log( "kill");
      kill( getppid(), SIGUSR1);
      p_log( "sleep");
      sleep( 1);
      p_log( "_exit");
      _exit( 0);
   }
}

int   main( int argc, const char * argv[])
{
   struct sigaction   act;
   int                status;

   sigemptyset( &act.sa_mask);
   act.__sigaction_u.__sa_sigaction = signal_action;
   act.sa_flags = SA_SIGINFO|SA_RESTART;

   p_log( "sigaction");
   sigaction( SIGUSR1, &act, NULL);

   _test();
   _test();

   p_log( "wait");
   while( wait( &status) == -1);
   p_log( "wait");
   while( wait( &status) == -1);

   p_log( "_exit");
   _exit( 0);
}

------------------------------------------------------
As an ex-Atari employee, who has known both
high income and protracted unemployment,
I can assure you that nobody should enter programming
for the money.   -- Chris Crawford

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