DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:to:from:subject:message-id:date:mime-version
	:content-type:content-transfer-encoding; q=dns; s=default; b=rb2
	DBalBpycPoumiQWsuKQxkWL4tsLjf74DOzEcqUzJYn8ew+smG6/MZOTf1cjah6Sz
	xigc/rNwYm9th3M3hgcT1k9G7PQBDCGaz35JQbkY9ixoOCrs9hMgFkGLt9IO0KSX
	RhSQupfZ1iwB/QEFfrxhA4zEEL5sTalzUdr/unYY=
Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm
Sender: cygwin-owner@cygwin.com
Mail-Followup-To: cygwin@cygwin.com
To: cygwin@cygwin.com
From: =?UTF-8?B?UGV0ciBTa2/EjcOtaw==?= <pskocik@gmail.com>
Subject: Weird behavior with writes to a unix socket pair
Message-ID: <6c7635fa-ae36-0c3b-d6fc-979c3d0448a9@gmail.com>
Date: Thu, 26 Sep 2019 16:38:21 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit

Hi,

I've been testing the effects of the SO_RCVBUF/SO_SNDBUF socket options
on unix sockets on various platforms, and I've run into some curious
unix socket behavior on Cygwin (independent of the SO_RCVBUF/SO_SNDBUF
options).


This piece of code should get blocked in one of the writes (and it does
so for regular pipes):


#include <sys/socket.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
	int p[2];
	socketpair(AF_LOCAL, SOCK_STREAM, 0,p);
	/*pipe(p);*/
	/*setsockopt(p[0], SOL_SOCKET, SO_RCVBUF, &(int){1},sizeof(int));*/
	/*setsockopt(p[0], SOL_SOCKET, SO_SNDBUF, &(int){1},sizeof(int));*/
	/*setsockopt(p[1], SOL_SOCKET, SO_RCVBUF, &(int){1},sizeof(int));*/
	/*setsockopt(p[1], SOL_SOCKET, SO_SNDBUF, &(int){1},sizeof(int));*/
	ssize_t n;
	for(unsigned j=0;j<10000;j++)
		for(unsigned char i=1; i!=0; i++){
			printf("%u\n", j*256+i);
			if(0>(n=write(p[1],&i,1))) perror("write");
		}


}

but with a unix socket socket pair a first couple of writes proceed
quickly and then the writes continue to proceed with ever-increasing
intervals between them.

I don't see why it should behave like this and I think you guys might
want to look into why it does.

Best regards,
Petr Skocik


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