Sv: Sv: Sv: Named pipes and multiple writers
Fri Mar 27 22:56:09 GMT 2020
On 3/27/2020 10:53 AM, firstname.lastname@example.org 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, email@example.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:
657 error: 6 No such device or address
658659 error: child 660
error: 66606661 661 661
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
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?
More information about the Cygwin