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/*-
* Copyright (c) 2009 Robert N. M. Watson
* All rights reserved.
*
* This software was developed at the University of Cambridge Computer
* Laboratory with support from a grant from Google, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
/*
* When a multi-threaded application calls fork(2) from one thread while
* another thread is blocked in accept(2), we prefer that the file descriptor
* to be returned by accept(2) not appear in the child process. Test this by
* creating a thread blocked in accept(2), then forking a child and seeing if
* the fd it would have returned is defined in the child or not.
*/
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define PORT 9000
static int listen_fd;
static void *
do_accept(__unused void *arg)
{
int accept_fd;
accept_fd = accept(listen_fd, NULL, NULL);
if (accept_fd < 0)
err(-1, "accept");
return (NULL);
}
static void
do_fork(void)
{
int pid;
pid = fork();
if (pid < 0)
err(-1, "fork");
if (pid > 0) {
waitpid(pid, NULL, 0);
exit(0);
}
/*
* We will call ftruncate(2) on the next available file descriptor,
* listen_fd+1, and get back EBADF if it's not a valid descriptor,
* and EINVAL if it is. This (currently) works fine in practice.
*/
if (ftruncate(listen_fd + 1, 0 < 0)) {
if (errno == EBADF)
exit(0);
else if (errno == EINVAL)
errx(-1, "file descriptor still open in child");
else
err(-1, "unexpected error");
} else
errx(-1, "ftruncate succeeded");
}
int
main(__unused int argc, __unused char *argv[])
{
struct sockaddr_in sin;
pthread_t accept_thread;
listen_fd = socket(PF_INET, SOCK_STREAM, 0);
if (listen_fd < 0)
err(-1, "socket");
bzero(&sin, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_len = sizeof(sin);
sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
sin.sin_port = htons(PORT);
if (bind(listen_fd, (struct sockaddr *)&sin, sizeof(sin)) < 0)
err(-1, "bind");
if (listen(listen_fd, -1) <0)
err(-1, "listen");
if (pthread_create(&accept_thread, NULL, do_accept, NULL) != 0)
err(-1, "pthread_create");
sleep(1); /* Easier than using a CV. */;
do_fork();
exit(0);
}
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