select_bug.c

[詳解]

/*++
/* NAME
/*  select_bug 1
/* SUMMARY
/*  select test program
/* SYNOPSIS
/*  select_bug
/* DESCRIPTION
/*  select_bug forks child processes that perform select()
/*  on a shared socket, and sees if a wakeup affects other
/*  processes selecting on a different socket or stdin.
/* DIAGNOSTICS
/*  Problems are reported to the standard error stream.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>         /* bzero() prototype for 44BSD */

/* Utility library. */

#include <msg.h>
#include <vstream.h>
#include <msg_vstream.h>

static pid_t fork_and_read_select(const char *what, int delay, int fd)
{
    struct timeval tv;
    pid_t   pid;
    fd_set  readfds;

    switch (pid = fork()) {
    case -1:
    msg_fatal("fork: %m");
    case 0:
    tv.tv_sec = delay;
    tv.tv_usec = 0;
    FD_ZERO(&readfds);
    FD_SET(fd, &readfds);
    switch (select(fd + 1, &readfds, (fd_set *) 0, &readfds, &tv)) {
    case -1:
        msg_fatal("select: %m");
    case 0:
        msg_info("%s select timed out", what);
        exit(0);
    default:
        msg_info("%s select wakeup", what);
        exit(0);
    }
    default:
    return (pid);
    }
}

int     main(int argc, char **argv)
{
    int     pair1[2];
    int     pair2[2];

    msg_vstream_init(argv[0], VSTREAM_ERR);

#define DELAY 1

    if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair1) < 0)
    msg_fatal("socketpair: %m");
    if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair2) < 0)
    msg_fatal("socketpair: %m");

    vstream_printf("Doing multiple select on socket1, then write to it...\n");
    vstream_fflush(VSTREAM_OUT);
    fork_and_read_select("socket1", DELAY, pair1[0]);   /* one */
    fork_and_read_select("socket1", DELAY, pair1[0]);   /* two */
    fork_and_read_select("socket2", DELAY, pair2[0]);
    fork_and_read_select("stdin", DELAY, 0);
    if (write(pair1[1], "", 1) != 1)
    msg_fatal("write: %m");
    while (wait((int *) 0) >= 0)
     /* void */ ;
    return (0);
}