altio/demo_sigio.c

/* demo_sigio.c

   A trivial example of the use of signal-driven I/O.
*/
#include <signal.h>
#include <ctype.h>
#include <fcntl.h>
#include <termios.h>
#include "tty_functions.h"      /* Declaration of ttySetCbreak() */
#include "tlpi_hdr.h"

static volatile sig_atomic_t gotSigio = 0;
                                /* Set nonzero on receipt of SIGIO */

static void
sigioHandler(int sig)
{
    gotSigio = 1;
}

int
main(int argc, char *argv[])
{
    int flags, j, cnt;
    struct termios origTermios;
    char ch;
    struct sigaction sa;
    Boolean done;

    /* Establish handler for "I/O possible" signal */

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = sigioHandler;
    if (sigaction(SIGIO, &sa, NULL) == -1)
        errExit("sigaction");

    /* Set owner process that is to receive "I/O possible" signal */

    if (fcntl(STDIN_FILENO, F_SETOWN, getpid()) == -1)
        errExit("fcntl(F_SETOWN)");

    /* Enable "I/O possible" signaling and make I/O nonblocking
       for file descriptor */

    flags = fcntl(STDIN_FILENO, F_GETFL);
    if (fcntl(STDIN_FILENO, F_SETFL, flags | O_ASYNC | O_NONBLOCK) == -1)
        errExit("fcntl(F_SETFL)");

    /* Place terminal in cbreak mode */

    if (ttySetCbreak(STDIN_FILENO, &origTermios) == -1)
        errExit("ttySetCbreak");

    for (done = FALSE, cnt = 0; !done ; cnt++) {
        for (j = 0; j < 100000000; j++)
            continue;                   /* Slow main loop down a little */

        if (gotSigio) {                 /* Is input available? */
            gotSigio = 0;

            /* Read all available input until error (probably EAGAIN)
               or EOF (not actually possible in cbreak mode) or a
               hash (#) character is read */

            while (read(STDIN_FILENO, &ch, 1) > 0 && !done) {
                printf("cnt=%d; read %c\n", cnt, ch);
                done = ch == '#';
            }
        }
    }

    /* Restore original terminal settings */

    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &origTermios) == -1)
        errExit("tcsetattr");
    exit(EXIT_SUCCESS);
}