trap

/*
 * call-seq:
 *   Signal.trap( signal, proc ) => obj
 *   Signal.trap( signal ) {| | block } => obj
 *
 * Specifies the handling of signals. The first parameter is a signal
 * name (a string such as ``SIGALRM'', ``SIGUSR1'', and so on) or a
 * signal number. The characters ``SIG'' may be omitted from the
 * signal name. The command or block specifies code to be run when the
 * signal is raised. If the command is the string ``IGNORE'' or
 * ``SIG_IGN'', the signal will be ignored. If the command is
 * ``DEFAULT'' or ``SIG_DFL'', the operating system's default handler
 * will be invoked. If the command is ``EXIT'', the script will be
 * terminated by the signal. Otherwise, the given command or block
 * will be run.
 * The special signal name ``EXIT'' or signal number zero will be
 * invoked just prior to program termination.
 * trap returns the previous handler for the given signal.
 *
 *     Signal.trap(0, proc { puts "Terminating: #{$$}" })
 *     Signal.trap("CLD")  { puts "Child died" }
 *     fork && Process.wait
 *
 * produces:
 *     Terminating: 27461
 *     Child died
 *     Terminating: 27460
 */
static VALUE
sig_trap(argc, argv)
    int argc;
    VALUE *argv;
{
    struct trap_arg arg;

    rb_secure(2);
    if (argc == 0 || argc > 2) {
        rb_raise(rb_eArgError, "wrong number of arguments -- trap(sig, cmd)/trap(sig){...}");
    }

    arg.sig = argv[0];
    if (argc == 1) {
        arg.cmd = rb_block_proc();
    }
    else if (argc == 2) {
        arg.cmd = argv[1];
    }

    if (OBJ_TAINTED(arg.cmd)) {
        rb_raise(rb_eSecurityError, "Insecure: tainted signal trap");
    }
#if USE_TRAP_MASK
    /* disable interrupt */
# ifdef HAVE_SIGPROCMASK
    sigfillset(&arg.mask);
    sigprocmask(SIG_BLOCK, &arg.mask, &arg.mask);
# else
    arg.mask = sigblock(~0);
# endif

    return rb_ensure(trap, (VALUE)&arg, trap_ensure, (VALUE)&arg);
#else
    return trap(&arg);
#endif
}