DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 43C573857815
Subject: Re: Unix Domain Socket Limitation?
From: Norton Allen <allen@huarp.harvard.edu>
To: Ken Brown <kbrown@cornell.edu>, cygwin <cygwin@cygwin.com>
References: <71490665-31b0-f63c-74da-461a053fac21@huarp.harvard.edu>
 <55ea1649-1979-6238-75ab-69100c22e069@cornell.edu>
 <4260ad1b-4ab2-fa36-fd0e-7c9644560114@huarp.harvard.edu>
 <38a82f82-1ef9-768e-7d3e-15f63147e188@cornell.edu>
 <a1f6e9af-7c0b-4d3f-4198-1c7bff4869dc@huarp.harvard.edu>
 <16165727-f614-1543-70bc-36457ddbf260@cornell.edu>
 <75d1315b-5a56-a2e5-310d-6ac33a3cf17c@huarp.harvard.edu>
 <f5373cd4-1d3e-500a-a967-1c558541e720@cornell.edu>
 <85c9c70f-c016-0f88-099e-5c772adbc648@huarp.harvard.edu>
Message-ID: <fb523694-7775-1d7a-db55-27ccbd6d157c@huarp.harvard.edu>
Date: Mon, 30 Nov 2020 21:22:56 -0500
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.5.0
MIME-Version: 1.0
In-Reply-To: <85c9c70f-c016-0f88-099e-5c772adbc648@huarp.harvard.edu>
Content-Language: en-US
Precedence: list
Content-Type: text/plain; charset="windows-1252"; Format="flowed"
Errors-To: cygwin-bounces@cygwin.com
Sender: "Cygwin" <cygwin-bounces@cygwin.com>
Content-Transfer-Encoding: 8bit

On 11/30/2020 9:14 PM, Norton Allen wrote:
> On 11/30/2020 6:19 PM, Ken Brown wrote:
>> On 11/30/2020 1:26 PM, Norton Allen wrote:
>>> On 11/30/2020 1:14 PM, Ken Brown wrote:
>>>> I can reproduce the hang, and it happens if I use the new AF_UNIX 
>>>> code also. But what I'm seeing (at least with the new code) isn't 
>>>> exactly what you describe.
>>>>
>>>> When the server's first select call returns, accept succeeds. The 
>>>> server then calls select a second time, and that call doesn't 
>>>> return. I haven't checked yet to see what's going on in the client, 
>>>> and I may not get to that for a while.
>>>>
>>> That's good news, and seems to be consistent with my theory that it 
>>> is some sort of race condition that might be particularly sensitive 
>>> to system-specific timing. I am compiling cygwin1.dll now.
>>
>> Hi Norton,
>>
>> I think there's a mistake in your test program.  Shouldn't 
>> client_pselect() be waiting for the socket to be write-ready rather 
>> than read-ready?  Here's a quote from the Posix page for 'connect':
>>
>> If the connection cannot be established immediately and O_NONBLOCK is 
>> set for the file descriptor for the socket, connect() shall fail and 
>> set errno to [EINPROGRESS], but the connection request shall not be 
>> aborted, and the connection shall be established asynchronously....
>>
>> When the connection has been established asynchronously, pselect(), 
>> select(), and poll() shall indicate that the file descriptor for the 
>> socket is ready for writing.
>>
> Yes, you are correct. In fact I had already fixed that bug on another 
> branch, then forgot to update it on this one. I also noticed another 
> bug in calculating width. Now I am not getting the blocking behavior 
> but instead getting the wrong bits set in select(). I think I'd better 
> pick this up in the morning when I am thinking straight!

Yeah, so now the example no longer blocks for me. Unfortunately these 
bugs are not present in my application, so I will need to keep working 
on this.


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