The Linux Programming Interface

432 Chapter 21

Note that using #ifdef was the simplest way of writing the program in Listing 21-2

in a standards-conformant fashion. In particular, we could not have replaced the

#ifdef with the following run-time check:

if (useSiglongjmp)

s = sigsetjmp(senv, 1);

else

s = setjmp(env);

if (s == 0)

...

This is not permitted because SUSv3 doesn’t allow setjmp() and sigsetjmp() to be used

within an assignment statement (see Section 6.8).

Listing 21-2: Performing a nonlocal goto from a signal handler

––––––––––––––––––––––––––––––––––––––––––––––––––signals/sigmask_longjmp.c

#define _GNU_SOURCE /* Get strsignal() declaration from <string.h> */

#include <string.h>

#include <setjmp.h>

#include <signal.h>

#include "signal_functions.h" /* Declaration of printSigMask() */

#include "tlpi_hdr.h"

static volatile sig_atomic_t canJump = 0;

/* Set to 1 once "env" buffer has been

initialized by [sig]setjmp() */

#ifdef USE_SIGSETJMP

static sigjmp_buf senv;

#else

static jmp_buf env;

#endif

static void

handler(int sig)

{

/* UNSAFE: This handler uses non-async-signal-safe functions

(printf(), strsignal(), printSigMask(); see Section 21.1.2) */

printf("Received signal %d (%s), signal mask is:\n", sig,

strsignal(sig));

printSigMask(stdout, NULL);

if (!canJump) {

printf("'env' buffer not yet set, doing a simple return\n");

return;

}

#ifdef USE_SIGSETJMP

siglongjmp(senv, 1);

#else

longjmp(env, 1);

#endif

}