Date: Wed, 23 Mar 2011 16:14:24 -0400
From: Christopher Faylor <cgf-use-the-mailinglist-please@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: python select() is limited to fds < 64
Message-ID: <20110323201424.GD5588@ednor.casa.cgf.cx>
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On Wed, Mar 23, 2011 at 04:38:15PM +0000, Jon TURNEY wrote:
>On 23/03/2011 15:00, Christopher Faylor wrote:
>> On Wed, Mar 23, 2011 at 11:31:46AM +0000, Jon TURNEY wrote:
>>> On 22/03/2011 20:08, Christopher Faylor wrote:
>>>> On Tue, Mar 22, 2011 at 08:53:34PM +0100, V??clav Haisman wrote:
>>>>> Jon TURNEY wrote, On 22.3.2011 20:29:
>>>>>>
>>>>>> python seems to be built with the default value of FD_SETSIZE, which is
>>>>>> only 64 on cygwin.
>>>>> Is this not because of the inherent limitation of
>>>>> WaitForMultipleObjects() call?
>>>>
>>>> Yep.  Without a rewrite, it's a hard limit to Cygwin's select().
>>>
>>> Please read my email more closely.  I am not saying "python select() is
>>> limited to waiting on 64 fds or less", I am saying "python select() is
>>> limited to waiting on fd which are less than 64"
>> 
>> I forgot to add one bit of data.  Unless you go out of your way to
>> change it, Cygwin's select can't wait for an fd > 63.  It's basically a
>> bit mask.  So, there are two limitations: 1) the number of handles that
>> you can wait for with WaitForMultipleObjects() and 2) the size of
>> Cygwin's fd_set.
>
>Yes, I know fd_set is implemented as a bitmap.  It's size is controlled by
>FD_SETSIZE.  That is the whole point of the patch in the original mail.

I actually did see that last night and then promptly forgot it.

I assume you know that this greately increases the likelihood that
select() will fail with an EINVAL.  Maybe python somehow deals
gracefully with that.

cgf

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