[OpenVMS, CRTL, V8.3-1H1, V8.4] sigsetjmp and siglongjmp working only once


PRODUCT:    HP C RTL V8.3-01
            HP C RTL V8.4-00 


OP/SYS:     OpenVMS IA64 V8.3-1H1 and above


COMPONENT:  sigsetjmp and siglongjmp 


SOURCE:     Philippe Vouters
            Fontainebleau/France


LOW-COST HIGH-TECH:  http://techno-star.fr


SYMPTOM(S) or PROBLEM(S):

sigsetjmp and siglongjmp run correctly only once on an OpenVMS system.


SOLUTION or RESPONSE:

A sigsetjmp and siglongjmp pair works only once on OpenVMS V8.3-1H1 and above
systems. If you are porting Unix code onto OpenVMS, your Unix code algorythm
being close to what is in the PROGRAM section of this document, you should
consider delay your port work until this problem is correctly addressed by the
HP C RTL.


WORKAROUND or ALTERNATIVE:

No workaround using sigsetjmp and siglongjmp. This is just a VMS incompatibility
of the C RTL with the Unix world.


PROGRAM OUTPUT:

The source code in the PROGRAM section of this document behaves the following:

OpenVMS IA64 V8.3-1H1 and above systems:
$ cc signal_unix.c
$ link signal_unix.c
$ spawn/nowait run signal_unix
%DCL-S-SPAWNED, process PHV_58176 spawned
$ 
  Type in $ kill -USR2 539359686
$ cc kill
$ link kill
$ kill :== $phv:[phv]kill
$ kill THESEE PHV_58176 SIGUSR2
In handlerSigusr2 for pid=539359686
 Returned to main
$ kill THESEE PHV_58176 SIGUSR2
$ kill THESEE PHV_58176 SIGUSR2

Linux Fedora 15 system:
$ cc -o signal_unix signal_unix.c
$ ./signal_unix &
[1] 25309
$ Type in $ kill -USR2 25309

$ kill -USR2 25309
In handlerSigusr2 for pid=25309
Returned to main
$ kill -USR2 25309
In handlerSigusr2 for pid=25309
Returned to main
$ kill -USR2 25309
In handlerSigusr2 for pid=25309
Returned to main
$ kill -USR2 25309
In handlerSigusr2 for pid=25309
Returned to main


ANALYSIS:

The Linux Fedora 15 behavior of the code in the PROGRAM section is what is
expected. On OpenVMS, the C RTL seems to save the pause() call stack in the
environment_buffer variable at the second sigsetjmp call invocation. Hence,
the siglongjmp seemlingly resuming the program into the pause() statement
after the second external kill.


PROGRAM:

/*
 *       Copyright (C) 2011 by Philippe.Vouters@laposte.net
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by the
 *   Free Software Foundation, either version 3 of the License, or
 *   any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>;.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <setjmp.h>
#include <sys/types.h>
#include <unistd.h>

sigjmp_buf environment_buffer;
pid_t main_pid;
struct sigaction sa;

static void handlerSIGUSR2(int);

static void trap_signals(struct sigaction *sa) {
    sa->sa_handler = handlerSIGUSR2;
    sigemptyset(&sa->sa_mask);
    sa->sa_flags = SA_RESETHAND;
    if(sigaction(SIGUSR2, sa, 0)){
       perror("sigaction");
       exit(EXIT_FAILURE);
    }
}

static void handlerSIGUSR2(int ArgIgnore){
   printf ("In handlerSigusr2 for pid=%1u\n",getpid());
   trap_signals(&sa);
   siglongjmp (environment_buffer,1) ;
   return;
}

int main(int argc, char **argv){
    pid_t pid;

    main_pid=getpid();
    trap_signals(&sa);
    printf("Type in $ kill -USR2 %1u\n", main_pid);
                                                              
    if (sigsetjmp(environment_buffer,1) == 1)
        printf ("Returned to main\n");
    pause();
    return 0;
}