signals/sigmask_longjmp.c

+/* sigmask_longjmp.c
+
+   Demonstrate the different effects of longjmp() and siglongjmp()
+   on the process signal mask.
+
+   By default, this program uses setjmp() + longjmp(). Compile with
+   -DUSE_SIGSETJMP to use sigsetjmp() + siglongjmp().
+*/
 #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
 }
 
 int
 main(int argc, char *argv[])
 {
     struct sigaction sa;
 
     printSigMask(stdout, "Signal mask at startup:\n");
 
     sigemptyset(&sa.sa_mask);
     sa.sa_flags = 0;
     sa.sa_handler = handler;
     if (sigaction(SIGINT, &sa, NULL) == -1)
         errExit("sigaction");
 
 #ifdef USE_SIGSETJMP
     printf("Calling sigsetjmp()\n");
     if (sigsetjmp(senv, 1) == 0)
 #else
     printf("Calling setjmp()\n");
     if (setjmp(env) == 0)
 #endif
         canJump = 1;                    /* Executed after [sig]setjmp() */
 
     else                                /* Executed after [sig]longjmp() */
         printSigMask(stdout, "After jump from handler, signal mask is:\n" );
 
     for (;;)                            /* Wait for signals until killed */
         pause();
 }