From: Norton Allen <allen@huarp.harvard.edu>
To: Ken Brown <kbrown@cornell.edu>, cygwin <cygwin@cygwin.com>
Subject: Re: Unix Domain Socket Limitation?
Date: Wed, 2 Dec 2020 12:30:51 -0500 [thread overview]
Message-ID: <1a0944b7-5924-31ab-7198-a5c311f39e06@huarp.harvard.edu> (raw)
In-Reply-To: <fb523694-7775-1d7a-db55-27ccbd6d157c@huarp.harvard.edu>
On 11/30/2020 9:22 PM, Norton Allen wrote:
> 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.
>
After paring the main application down and back up, I finally narrowed
in on the condition that was causing this blocking behavior. The issue
arises when a client connect()s twice to the same server with
non-blocking unix-domain sockets before calling select().
There are a few pieces to this. With the client configured to connect()
just once, I can see that the server's select() returns as soon as the
client calls connect(), but then the server's accept() blocks until the
client calls select(). That is not proper non-blocking behavior, but it
appears that the implementation under Cygwin does require that client
and server both be communicating synchronously to accomplish the
connect() operation.
I tried running this under Ubuntu 16.04 and found that connect()
succeeded immediately, so no subsequent select() is required, and there
does not appear to be a possibility for this collision. That proves to
hold true even if the server is not waiting in select() to process the
connect() with accept().
A workaround for this issue may be to keep the socket blocking until
after connect().
I have pushed the new minimal example program, 'rapid_connects' to
https://github.com/nthallen/cygwin_unix
The server is run like before as:
$ ./rapid_connects server
The client can be run in two different modes. To connect with just one
socket:
$ ./rapid_connects client1
To connect with two:
$ ./rapid_connects client2
My immediate strategy will be to develop a workaround for my project.
Having spent a day inside cygwin1.dll, I can see that I have a steep
learning curve to make much of a contribution there.
next prev parent reply other threads:[~2020-12-02 17:30 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-25 21:47 Norton Allen
2020-11-25 22:27 ` Ken Brown
[not found] ` <4260ad1b-4ab2-fa36-fd0e-7c9644560114@huarp.harvard.edu>
2020-11-26 17:13 ` Ken Brown
2020-11-30 17:19 ` Norton Allen
2020-11-30 18:14 ` Ken Brown
2020-11-30 18:26 ` Norton Allen
2020-11-30 23:19 ` Ken Brown
2020-12-01 2:14 ` Norton Allen
2020-12-01 2:22 ` Norton Allen
2020-12-02 17:30 ` Norton Allen [this message]
2020-12-04 1:11 ` Ken Brown
2020-12-04 13:51 ` Norton Allen
2020-12-05 23:52 ` Ken Brown
2020-12-06 17:17 ` Norton Allen
2020-12-06 22:32 ` Ken Brown
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