On Fri, 7 Oct 2011, Michael Kerrisk wrote:
> Hi Lukas
>
> On Fri, Oct 7, 2011 at 9:09 AM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
> > On Fri, 7 Oct 2011, Michael Kerrisk wrote:
> >
> >> Lukas,
> >>
> >> On Mon, Aug 29, 2011 at 2:26 PM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
> >> > When dealing with sockets, we have to be sure that there is no recv
> >> > still blocking on it on another thread, otherwise it might block forever,
> >> > since no more messages will be send via the socket. We should advice to
> >> > use shutdown before closing socket.
> >>
> >> I'm looking into this now. The picture may be more complex than this.
> >> Tell me, so you have a Solaris system available for testing?
> >>
> >> Thanks,
> >
> > Hi Michael,
> >
> > Thanks for looking into this. Unfortunately I do not have any Solaris system
> > for testing, that was a customer report. His complaint was mainly not because
> > the behaviour on Linux differs, but because this was not documented anywhere.
>
> Okay. I will see if I can find a test system somewhere. (The system I
> used to use seems to have gone away.)
>
> Just FYI: I confirmed what you are seeing, but the issue seems more
> general: basically, closing a file descriptor in one thread while
> reading in another thread does not cause the read operation to
> terminate (it will still read data if/when it becomes available).
>
> By the way, I'm wondering about creating a small repo of test
> programs. I might like to add a modified version of your test program
> to that repo. Can you put that code under a Free License and supply a
> copyright?
>
> Thanks,
>
> Michael
Hi Michael,
no problem, here is the program, feel free to update it as you like.
Thanks for looking into this.
-Lukas
---
/**
* Copyright 2011 (C) Red Hat, Inc., Lukas Czerner <lczerner@xxxxxxxxxx>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it would be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/un.h>
#include <unistd.h>
#include <pthread.h>
#define BUFSIZE 1024
void *close_socket(void *arg) {
int sockfd = *(int *)arg;
sleep(3);
printf("Thread: closing socket %d\n", sockfd);
// shutdown(sockfd, SHUT_RDWR);
close(sockfd);
}
int client(void) {
int sockfd;
int len;
struct sockaddr_un address;
int ret;
char *buffer=malloc(BUFSIZE);
pthread_t thread;
sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
address.sun_family = AF_UNIX;
strcpy(address.sun_path, "server_socket");
len = sizeof(address);
ret = connect(sockfd, (struct sockaddr *)&address, len);
if (ret == -1) {
perror("connect");
return 1;
}
printf("client connected\n");
ret = pthread_create(&thread, NULL, close_socket, (void *)&sockfd);
if (ret != 0) {
perror("Creating thread failed");
return 1;
}
while (1) {
ret = recv(sockfd,buffer,BUFSIZE,0);
if (ret < 0) {
perror("recv");
return 1;
}
printf("Data received: %s\n", buffer);
sleep(1);
}
close(sockfd);
return 0;
}
int server(void) {
char *message="This is the message I am sending to you";
struct sockaddr_un server_addr, client_addr;
int server_sockfd, client_sockfd;
int server_len, client_len;
int ret;
unlink("server_socket");
server_sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
server_addr.sun_family = AF_UNIX;
strcpy(server_addr.sun_path, "server_socket");
server_len = sizeof(server_addr);
bind(server_sockfd, (struct sockaddr *)&server_addr, server_len);
listen(server_sockfd, 5);
client_len = sizeof(client_addr);
client_sockfd = accept(server_sockfd,
(struct sockaddr *)&client_addr, &client_len);
printf("Server: sending data...\n");
ret = send(client_sockfd ,message,strlen(message),0);
if (ret < 0) {
perror("send");
return 1;
}
/* simulate running server by not closing the client_socket socket */
return 0;
}
int main() {
pid_t pid;
int n;
pid = fork();
if (pid < 0) {
perror("fork failed");
exit(1);
}
if (pid > 0) {
printf(" - starting server\n");
server();
printf(" - exiting server\n");
wait();
} else {
sleep(1);
printf(" - starting client\n");
client();
printf(" - exiting client\n");
}
}
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