From: Ken Brown <kbrown@cornell.edu>
To: sten.kristian.ivarsson@gmail.com
Cc: 'cygwin' <cygwin@cygwin.com>
Subject: Re: Sv: Sv: Sv: Named pipes and multiple writers
Date: Fri, 27 Mar 2020 18:56:09 -0400 [thread overview]
Message-ID: <f8f5c9b4-9eb9-85b0-ab8f-44b3b2458e0b@cornell.edu> (raw)
In-Reply-To: <00b901d60447$7ecb4c50$7c61e4f0$@gmail.com>
On 3/27/2020 10:53 AM, sten.kristian.ivarsson@gmail.com wrote:
>> On 3/26/2020 7:19 PM, Ken Brown via Cygwin wrote:
>>> On 3/26/2020 6:39 PM, Ken Brown via Cygwin wrote:
>>>> On 3/26/2020 6:01 PM, sten.kristian.ivarsson@gmail.com wrote:
>>>>> The ENIXIO occurs when parallel child-processes simultaneously using
>>>>> O_NONBLOCK opening the descriptor.
>>>>
>>>> This is consistent with my guess that the error is generated by
>>>> fhandler_fifo::wait. I have a feeling that read_ready should have
>>>> been created as a manual-reset event, and that more care is needed to
>>>> make sure it's set when it should be.
>>>>
>>>>> I could provide a code-snippet
>>>>> to reproduce it if wanted ?
>>>>
>>>> Yes, please!
>>>
>>> That might not be necessary. If you're able to build the git repo
>>> master branch, please try the attached patch.
>
>> Here's a better patch.
>
>
> I finally succeeded to build latest master (make is not my favourite tool)
> and added the patch, but still no success in my little test-program (see
> attachment) when creating a write-file-descriptor with O_NONBLOCK
Your test program fails for me on Linux too. Here's the output from one run:
child 657
657 error: 6 No such device or address
child 658
child 659
658659 error: child 660
parent
child 661
error: 66606661 661 661
error: 661
No such device or address6No such device or address
No such device or address
[I then killed it with control-C; the parent was blocked trying to open the FIFO.]
There's a race condition in your code. The parent is trying to open the FIFO
for reading (without O_NONBLOCK) while the child is trying to open it for
writing (with O_NONBLOCK). The parent is blocked waiting for the child, and the
child's open fails with ENXIO; see
https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html#tag_16_357
I think you need to rearrange things so that the FIFO is open for reading before
you try a nonblocking open for writing.
I can work around the race by using a small positive 'wait' in
fhandler_fifo::wait(), but I'm not sure this is the right thing to do, since
Cygwin aims to emulate Linux. Can you find a test case that works on Linux but
fails on Cygwin?
Ken
next prev parent reply other threads:[~2020-03-27 22:56 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 11:11 sten.kristian.ivarsson
2020-03-25 12:44 ` Ken Brown
[not found] ` <18be01d602ab$0bbfca30$233f5e90$@gmail.com>
2020-03-26 14:06 ` Sv: " Ken Brown
2020-03-26 15:11 ` Ken Brown
2020-03-26 16:03 ` Norton Allen
2020-03-26 16:44 ` Ken Brown
2020-03-26 17:00 ` Norton Allen
2020-03-26 22:01 ` Sv: " sten.kristian.ivarsson
2020-03-26 22:39 ` Ken Brown
2020-03-26 23:19 ` Ken Brown
2020-03-27 13:10 ` Ken Brown
2020-03-27 14:53 ` Sv: " sten.kristian.ivarsson
2020-03-27 22:56 ` Ken Brown [this message]
2020-03-27 23:00 ` Ken Brown
2020-03-28 12:10 ` Sv: " sten.kristian.ivarsson
2020-03-28 15:43 ` Ken Brown
2020-03-29 2:19 ` Ken Brown
2020-03-30 17:44 ` Ken Brown
2020-03-31 21:10 ` Sv: " sten.kristian.ivarsson
2020-03-31 22:02 ` Ken Brown
2020-04-01 7:45 ` Sv: " sten.kristian.ivarsson
2020-04-01 13:47 ` Ken Brown
2020-04-01 8:52 ` sten.kristian.ivarsson
2020-04-01 16:15 ` Ken Brown
2020-04-01 17:14 ` Sv: " sten.kristian.ivarsson
2020-04-01 18:34 ` Ken Brown
2020-04-02 2:19 ` Ken Brown
2020-04-02 8:05 ` Sv: " sten.kristian.ivarsson
2020-04-02 12:47 ` Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Named pipes and multiple wri Gregery Barton
2020-04-02 18:21 ` Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Named pipes and multiple writers Ken Brown
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