signals/signal.c

This is signals/signal.c (Listing 22-1, page 455), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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/* signal.c

   An implementation of signal() using sigaction().

   Compiling with "-DOLD_SIGS" provides the older, unreliable signal handler
   semantics (which are still the default on some System V derivatives).
*/
/* Some UNIX implementations follow the BSD signal() semantics, including
   Linux, Tru64, and of course the BSD derivatives. Others, such as Solaris,
   follow the System V semantics. We'll conditionally override signal() on
   platforms following the System V semantics. For the other implementations,
   we'll provide a dummy source file that doesn't implement signal().
*/
#if defined(__sun) || defined(__sgi)
#include <signal.h>

typedef void (*sighandler_t)(int);
sighandler_t
signal(int sig, sighandler_t handler)
{
    struct sigaction newDisp, prevDisp;

    newDisp.sa_handler = handler;
    sigemptyset(&newDisp.sa_mask);
#ifdef OLD_SIGNAL
    newDisp.sa_flags = SA_RESETHAND | SA_NODEFER;
#else
    newDisp.sa_flags = SA_RESTART;
#endif

    if (sigaction(sig, &newDisp, &prevDisp) == -1)
        return SIG_ERR;
    else
        return prevDisp.sa_handler;
}

#else
/* The following declaration is provided purely to avoid gcc's
   "warning: ISO C forbids an empty source file" warnings. */

extern int signalDummyVar;

#endif

 

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