Re: Questions about select for sockets

[Ken Brown <kbrown@cornell.edu>]

On 4/6/2021 3:36 PM, Corinna Vinschen wrote:
> On Apr  6 20:24, Corinna Vinschen wrote:
>> On Apr  6 13:37, Ken Brown wrote:
>>> On 4/6/2021 12:28 PM, Corinna Vinschen wrote:
>>>> On Apr  6 11:44, Ken Brown wrote:
>>>>> On 4/6/2021 10:33 AM, Corinna Vinschen wrote:
>>>>>> We may also have to change the saw_shutdown_read/saw_shutdown_write
>>>>>> handling.  I checked this on Linux and what happens is:
>>>>>>
>>>>>>      After shutdown (fd, SHUT_RD), the socket is ready for reading and writing
>>>>>
>>>>> This seems surprising to me.  Is it really the shutdown that caused it to be
>>>>> ready for writing in your test, or was it ready for writing anyway (e.g.,
>>>>> because the relevant buffer was empty)?
>>>>
>>>> I guess so, too.  How to make sure the socket isn't ready for writing
>>>> without going to great lengths?
>>>
>>> I guess you could have a subprocess write to the socket in a loop, so that
>>> its buffer will quickly fill up and a further write will block.
>>
>> Yeah, I was trying to minimize work, but I now lazily created a blocking
>> server in the same process with a non-blocking client, calling send(2)
>> until it fails.
>>
>> And now everything is as expected.  SHUT_RD -> ready for reading,
>> SHUT_WR -> ready for writing, SHUT_RDWR -> ready for both.
>>
>> I attached my STC, for completeness.  Call with an argument
>> 0 (== SHUT_RD), 1 (== SHUT_WR), or 2 (== SHUT_RDWR).
> 
> I pushed a patch to handle this better.  Please have a look.

You forgot this:

--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -528,6 +528,7 @@ set_bits (select_record *me, fd_set *readfds, fd_set *writefds,
           if (!me->read_ready && me->read_selected
               && sock->connect_state () == connect_failed)
             UNIX_FD_SET (me->fd, readfds);
+         ready++;
         }
        ready++;
      }

Otherwise it looks good to me, to the extent that I can judge.  I'm not at all 
familiar with the Winsock events.

Ken