X-Recipient: archive-cygwin AT delorie DOT com
X-Spam-Check-By: sourceware.org
Message-ID: <476185AF.5000906@4raccoons.com>
Date: Thu, 13 Dec 2007 11:19:11 -0800
From: Wayne Christopher <wayne AT 4raccoons DOT com>
User-Agent: Thunderbird 1.5.0.4 (X11/20060516)
MIME-Version: 1.0
To: cygwin AT cygwin DOT com
Subject: Re: VM and non-blocking writes
References: <47616D31 DOT 7090002 AT 4raccoons DOT com> <20071213175934 DOT GB25863 AT calimero DOT vinschen DOT de>
In-Reply-To: <20071213175934.GB25863@calimero.vinschen.de>
Content-Type: multipart/mixed;  boundary="------------020501020708040208080401"
X-IsSubscribed: yes
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id: <cygwin.cygwin.com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

--------------020501020708040208080401
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Okay, here's my test program.  Compile and run with no arguments, then
connect to it from another machine - on a linux box I just did:

python
import socket
s = socket.socket()
s.connect(("name-of-windows-box", 12345))

At this point, nbcheck printed:

listening to port 12345 on host xp1 (10.1.2.40)
got connection from 10.1.2.14
trying to write 100000000
100000000 bytes written

When I hit return to exit from nbcheck, it does not actually exit until
the remote socket is closed.

The VM usage is 100M, which is all the data array that I allocated, so
it doesn't look like the write() call allocated anything in my process
space.

This behavior makes some sense to me, but it's not how I expect it to
work (based on the write(2) man page and how it works on linux).  It's
more like asynchronous write than non-blocking write.  Using O_NONBLOCK
instead of O_NDELAY doesn't change the behavior.

Thanks,

     Wayne



--------------020501020708040208080401
Content-Type: text/x-c++src;
 name="nbcheck.c"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="nbcheck.c"


#include <stdio.h>
#include <ctype.h>
#include <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <assert.h>

main()
{
    int i, fd, fd2, len;
    struct hostent *hp;
    struct protoent *pp;
    char hostname[64];
    struct sockaddr_in lAddr, rAddr;
    char* data;
    int datalen, datapos;
    
    gethostname(hostname, 64);
    pp = getprotobyname("tcp");
    hp = gethostbyname(hostname);
    
    assert(pp && hp);
    
    fd = socket(AF_INET, SOCK_STREAM, pp->p_proto);
    assert(fd >= 0);
    
    lAddr.sin_family = hp->h_addrtype;
    memcpy((char *)&lAddr.sin_addr.s_addr, (char *)hp->h_addr,
	   sizeof(lAddr.sin_addr.s_addr));
    lAddr.sin_port = htons(12345);
    
    i = bind(fd, (struct sockaddr *)&lAddr, sizeof(lAddr));
    assert(i >= 0);
    
    printf("listening to port %d host %s (%s)\n", ntohs(lAddr.sin_port),
	   hostname, inet_ntoa(lAddr.sin_addr));
    i = listen(fd, 5);
    assert(i >= 0);
    
    len = sizeof(rAddr);
    memset(&rAddr, 0, sizeof(rAddr));
    fd2 = accept(fd, (struct sockaddr *)&rAddr, &len);
    assert(fd2 >= 0);
    
    printf("got connection from %s\n", inet_ntoa(rAddr.sin_addr));
    
    i = fcntl(fd2, F_SETFL, O_NDELAY);
    assert(i >= 0);
    
    datalen = (int) 1e8;
    data = (char *) malloc(datalen);
    datapos = 0;
    
    while (datapos < datalen) {
	fd_set wfds;
	FD_ZERO(&wfds);
	FD_SET(fd2, &wfds);
	
	i = select(fd2 + 1, NULL, &wfds, NULL, NULL);
	assert(i == 1);
	
	printf("trying to write %d bytes\n", datalen - datapos);
	i = write(fd2, data + datapos, datalen - datapos);
	printf("%d bytes written\n", i);
	assert(i > 0);
	
	datapos += i;
	assert(datapos <= datalen);
    }
    printf("hit return to exit ");
    getchar();
    exit(0);
}



--------------020501020708040208080401
Content-Type: text/plain; charset=us-ascii

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/
--------------020501020708040208080401--