Message-Id: <9603071857.AA08791@yaz-pistachio.MIT.EDU>
To: Ian Piumarta <piumarta@prof.inria.fr>
Cc: proven@MIT.EDU
Subject: Re: socket io and host lookup 
In-Reply-To: Your message of "Mon, 26 Feb 1996 15:18:58 +0100."
             <199602261418.PAA29265@atchoum.inria.fr> 
Date: Thu, 07 Mar 1996 13:57:17 EST
From: Christopher Provenzano  <proven@MIT.EDU>


> 
> Using Chris's pthreads it appears that I cannot have one thread blocked in a
> read() on a socket waiting for data to arrive, while another thread issues a
> write() to the same socket.  The read() returns -1 with errno set to 0.
> Using DEC's native pthreads implementation on an Alpha it works perfectly.
> 
> If course it's easy to fix by using back-to-back pairs of sockets, but this
> effectively halves the size of my descriptor table.  Is there any official
> position on this sort of "full-duplex" use of sockets in multiple threads?

I tried to duplicate your error and failed. COuld you send me a short example
along with information of which system you were doing this on? I've included
my test program (just a modified test_sock_1) below for you to test also. The 
output should look like ...

initial thread 15a98 going to sleep
This should be message #1
This should be message #2
This should be message #3
This should be message #4
This should be message #5
This should be message #6
done sleeping

> 
> 
> While I'm here I should also mention something else.  I think it is a serious
> shortcoming that gethostbyname() looks only in the DNS, and ignores
> /etc/hosts.  On our SunOS machines we first have a local resolution in
> /etc/hosts followed by a query to the DNS if no entry is found in the file.
> I noticed this when I took some work home: the code ran fine when my modem
> and PPP were up (and I had a DNS server at work to query), but failed with
> the modem switched off.  Taking out the pthreads stuff to get the native
> SunOS behaviour back, it worked with the modem on or off.
> 
> I suspect it's the same on OSF1 machines: we unplugged an Alpha a while ago
> and it ran just fine with only /etc/hosts and no DNS.
> 
> Is there any chance of fixing the behaviour for those poor people like myself
> who have to work on netless machines once in a while?  (And local calls *cost
> lots* over here, so that isn't a particularly viable solution... ;-)

Yes, that is a deficiency. I'll get working on it.
CAP


/* ==== test_sock_1.c ========================================================
 * Copyright (c) 1993 by Chris Provenzano, proven@athena.mit.edu
 *
 * Description : Test pthread_create() and pthread_exit() calls.
 *
 *  1.00 93/08/03 proven
 *      -Started coding this file.
 */

#include <pthread.h>
#include <errno.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

struct sockaddr_in a_sout;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_attr_t attr;

#define MESSAGE5 "This should be message #5"
#define MESSAGE6 "This should be message #6"

void * sock_connect(void* arg)
{
	char buf[1024];
	int fd, tmp;

	/* Ensure sock_read runs first */
	if (pthread_mutex_lock(&mutex)) {
		printf("Error: sock_connect:pthread_mutex_lock()\n");
		exit(1);
	}

	a_sout.sin_addr.s_addr = htonl(0x7f000001); /* loopback */

	if ((fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
		printf("Error: sock_connect:socket()\n");
		exit(1);
	}

	printf("This should be message #2\n");
	if (connect(fd, (struct sockaddr *) &a_sout, sizeof(a_sout)) < 0) {
		printf("Error: sock_connect:connect()\n");
		exit(1);
	}
	close(fd);
		
	if (pthread_mutex_unlock(&mutex)) {
		printf("Error: sock_connect:pthread_mutex_lock()\n");
		exit(1);
	}

	if ((fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
		printf("Error: sock_connect:socket()\n");
		exit(1);
	}

	printf("This should be message #3\n");

	if (connect(fd, (struct sockaddr *) &a_sout, sizeof(a_sout)) < 0) {
		printf("Error: sock_connect:connect()\n");
		exit(1);
	}

	/* Ensure sock_read runs again */
	pthread_yield();
	pthread_yield();
	pthread_yield();
	pthread_yield();
	if (pthread_mutex_lock(&mutex)) {
		printf("Error: sock_connect:pthread_mutex_lock()\n");
		exit(1);
	}

	if ((tmp = read(fd, buf, 1024)) <= 0) {
		printf("Error: sock_connect:read() == %d\n", tmp);
		exit(1);
	}
	write(fd, MESSAGE6, sizeof(MESSAGE6));
	printf("%s\n", buf);
	close(fd);
}

extern struct fd_table_entry ** fd_table;
void * sock_write(void* arg)
{
	int fd = *(int *)arg;

	write(fd, MESSAGE5, sizeof(MESSAGE5));
	return(NULL);
}

void * sock_accept(void* arg)
{
	pthread_t thread;
	struct sockaddr a_sin;
	int a_sin_size, a_fd, fd, tmp;
	short port;
	char buf[1024];

	if (pthread_mutex_unlock(&mutex)) {
		printf("Error: sock_accept:pthread_mutex_lock()\n");
		exit(1);
	}

	port = 3276;
	a_sout.sin_family = AF_INET;
	a_sout.sin_port = htons(port);
	a_sout.sin_addr.s_addr = INADDR_ANY;

	if ((a_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
		printf("Error: sock_accept:socket()\n");
		exit(1);
	}

	while (bind(a_fd, (struct sockaddr *) &a_sout, sizeof(a_sout)) < 0) {
		if (errno == EADDRINUSE) { 
			a_sout.sin_port = htons((++port));
			continue;
		}
		printf("Error: sock_accept:bind()\n");
		exit(1);
	}

	if (listen(a_fd, 2)) {
		printf("Error: sock_accept:listen()\n");
		exit(1);
	}
		
	a_sin_size = sizeof(a_sin);
	printf("This should be message #1\n");
	if ((fd = accept(a_fd, &a_sin, &a_sin_size)) < 0) {
		printf("Error: sock_accept:accept()\n");
		exit(1);
	}
	
	if (pthread_mutex_lock(&mutex)) {
		printf("Error: sock_accept:pthread_mutex_lock()\n");
		exit(1);
	}
	close(fd);

	a_sin_size = sizeof(a_sin);
	printf("This should be message #4\n");
	if ((fd = accept(a_fd, &a_sin, &a_sin_size)) < 0) {
		printf("Error: sock_accept:accept()\n");
		exit(1);
	}

	if (pthread_mutex_unlock(&mutex)) {
		printf("Error: sock_accept:pthread_mutex_lock()\n");
		exit(1);
	}

	/* Setup a write thread */
	if (pthread_create(&thread, &attr, sock_write, &fd)) {
		printf("Error: sock_accept:pthread_create(sock_write)\n");
		exit(1);
	}
	if ((tmp = read(fd, buf, 1024)) <= 0) {
		printf("Error: sock_accept:read() == %d\n", tmp);
		exit(1);
	}
	printf("%s\n", buf);
	close(fd);
}

main()
{
	pthread_t thread;
	int i;

	pthread_init(); 
	setbuf(stdout, NULL);
	setbuf(stderr, NULL);

	/* Ensure sock_read runs first */
	if (pthread_mutex_lock(&mutex)) {
		printf("Error: main:pthread_mutex_lock()\n");
		exit(1);
	}

	if (pthread_attr_init(&attr)) {
		printf("Error: main:pthread_attr_init()\n");
		exit(1);
	}
	if (pthread_attr_setschedpolicy(&attr, SCHED_FIFO)) {
		printf("Error: main:pthread_attr_setschedpolicy()\n");
		exit(1);
	}
	if (pthread_create(&thread, &attr, sock_accept, (void *)0xdeadbeaf)) {
		printf("Error: main:pthread_create(sock_accept)\n");
		exit(1);
	}
	if (pthread_create(&thread, &attr, sock_connect, (void *)0xdeadbeaf)) {
		printf("Error: main:pthread_create(sock_connect)\n");
		exit(1);
	}
	printf("initial thread %lx going to sleep\n", pthread_self());
	sleep(10);
	printf("done sleeping\n");
	return 0;
}