Unix Domain Socket Limitation?

Norton Allen allen@huarp.harvard.edu
Tue Dec 1 02:22:56 GMT 2020

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.

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