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From Jeff Trawick <traw...@gmail.com>
Subject Re: 100% cpu with APR on Windows
Date Fri, 06 May 2011 14:01:16 GMT
On Fri, May 6, 2011 at 4:28 AM, Eric van der Maarel
<eric.vandermaarel@nedap.com> wrote:
> On 05/05/2011 10:17 PM, Jeff Trawick wrote:
>>
>> On Thu, May 5, 2011 at 3:20 PM, Eric van der Maarel
>> <eric.vandermaarel@nedap.com>  wrote:
>>>
>>> Hi,
>>>
>>> Further investigation reveals a difference between running Tomcat on
>>> Linux and Windows. From the Tomcat Poller thread the apr_pollset_poll()
>>> is called. When a client in the pollset has disconnected, under Linux
>>> this call returns (in the rtnevents member of the descriptors resultset)
>>>    49 (=0x31, so that would be APR_POLLIN | APR_POLLERR | APR_POLLHUP),
>>> while under Windows this always return
>>>    1 (so APR_POLLIN)
>>>
>>> The poller in Tomcat reacts on the APR_POLLHUP result, so differently on
>>> Windows than on Linux. I think the problem lies in the missing
>>> APR_POLLHUP in the poll return result under Windows (from the
>>> impl_pollset_poll implemented in select.c by the way).
>>>
>>> Anyone any idea why on Windows (select.c) the rtnevents does not have
>>> the APR_POLLHUP flag up, while on Linux (no idea which poll provider
>>> version is used ther :-) this flag is set when the client has
>>> disconnected?
>>> And how to fix? :-)
>>
>> select() has a simpler view of things; normally something needs to
>> read from the readable socket, get connreset or equiv, and handle
>> closed connection at that point
>>
>> select() on any platform can't set APR_POLLHUP as a return event
>>
>> maybe getsockopt(SOL_SOCKET/SO_ERROR) when socket is readable and
>> APR_POLLHUP was requested would give the necessary info????
>
> Change the apr client you mean to handle receiving APR_POLLIN, right?
>
>
>
>
>>
>> --/--
>>
>> are you sure select() is being used?  newer Windows should have
>> WSApoll()?????
>
> Yes, select() is being used (added some logging to select.c that actually
> shows up). We're running on Windows XP (SP3) which, as I understand it,
> doesn't have WSAPoll().
> If XP does have WSAPoll(), how to enforce it? Is it determined buildtime or
> runtime which poll/pollset provider is going to be used?
> Can and should we use another provider than select on XP and how can that be
> configured? Or, for this use case, shouldn't we use XP altogether and use
> one of those server versions of Windows instead?

XP only has select() available.

WSAPoll() is available with Vista/2008 Server and later.  It should be
used automatically by APR without rebuilding your code (via a run-time
check for presence of the Windows API).

As far as WSAPoll() and this issue...  MS doc says

"POLLHUP	A stream-oriented connection was either disconnected or aborted."

POLLHUP is mapped to APR_POLLHUP.

(IOW, I didn't test but it looks promising.)

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