From: Ken Brown <kbrown@cornell.edu>
To: sten.kristian.ivarsson@gmail.com
Cc: 'cygwin' <cygwin@cygwin.com>
Subject: Re: Sv: Sv: Sv: Sv: Sv: Named pipes and multiple writers
Date: Tue, 31 Mar 2020 18:02:38 -0400 [thread overview]
Message-ID: <249be61e-da8a-7da1-ca67-0c4c6433a415@cornell.edu> (raw)
In-Reply-To: <003701d607a0$c975f140$5c61d3c0$@gmail.com>
On 3/31/2020 5:10 PM, sten.kristian.ivarsson@gmail.com wrote:
>> On 3/28/2020 10:19 PM, Ken Brown via Cygwin wrote:
>>> On 3/28/2020 11:43 AM, Ken Brown via Cygwin wrote:
>>>> On 3/28/2020 8:10 AM, sten.kristian.ivarsson@gmail.com wrote:
>>>>>> 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:
>>>>>
>>>>> You're right. That was extremely careless of me to not test this in
>>>>> Linux first :-)
>>>>
>>>> No problem.
>>>>
>>>>> I can assure that we have a use case that works on Linux but not in
>>>>> Cygwin, but it seems like I failed to narrow it down in the wrong
>>>>> way
>>>>>
>>>>> I'll try to rearrange my code (that works in Linux) to mimic our
>>>>> application but in a simple way (I'll be back)
>>>>
>>>> OK, I'll be waiting for you. BTW, if it's not too hard to write your
>>>> test case in plain C, or at least less modern C++, that would
>>>> simplify things for me. For example, your pipe.cpp failed to compile
>>>> on one Linux machine I wanted to test it on, presumably because that
> machine had an older C++ compiler.
>>>
>>> Never mind. I was able to reproduce the problem and find the cause.
>>> What happens is that when the first subprocess exits,
>>> fhandler_fifo::close resets read_ready. That causes the second and
>>> subsequent subprocesses to think that there's no reader open, so their
>>> attempts to open a writer with O_NONBLOCK fail with ENXIO.
>>>
>>> I should be able to fix this tomorrow.
>
>> I've pushed what I think is a fix to the topic/fifo branch. I tested it
> with the attached program, which is a variant of the test case you sent last
> week.
>> Please test it in your use case.
>
>> Note: If you've previously pulled the topic/fifo branch, then you will
> probably get a lot of conflicts when you pull again, because I did a forced
> push a few days ago. If that happens, just do
>
>> git reset --hard origin/topic/fifo
>
>> It turned out that the fix required some of the ideas that I've been
> working on in connection with allowing multiple readers. Even though the
> code allows a FIFO to be *explicitly* opened for reading only once, there
> can still be several open file descriptors for readers because of dup and
> fork. The existing code on git master doesn't handle those situations
> properly.
>
>> The code on topic/fifo doesn't completely fix that yet, but I think it
> should work under the following assumptions:
>
>> 1. The FIFO is opened only once for reading.
>
>> 2. The file descriptor obtained from this is the only one on which a read
> is attempted.
>
>> I'm working on removing both of these restrictions.
>
>> Ken
>
> We finally took the time to make some kind of a simplified "hack" that works
> on Ubuntu and BSD/OSX but with latest on master newlib-cygwin gave "ENXIO"
> now and then but with your previous patch attached, there was no ENXIO but
> ::read returns EAGIN (until exhausted) (with cygwin) almost every run
>
> I will try your newest things tomorrow
>
> See latest attatched test-program (starts to get bloated but this time more
> C-compatible though:-)
Thanks. This runs fine with the current HEAD of topic/fifo.
Ken
next prev parent reply other threads:[~2020-03-31 22:02 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
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 [this message]
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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