launchpad-dev team mailing list archive

[John Arbash Meinel <john@xxxxxxxxxxxxxxxxx>]

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Martin Pool wrote:
> On 17 August 2010 11:48, Michael Hudson <michael.hudson@xxxxxxxxxxxxx> wrote:
>>>>> The last is a bit of an approximation, because my test front end hack
>>>>> uses select.poll() over file descriptors, and doesn't seem to be getting
>>>>> POLLHUP on any of the fifos.
>>>> I don't entirely understand the consequence of this :-)
>>> So the big takeaway is 2.4s => 0.08s.
>> I understood that bit! :-)
>>
>>> There is some concern that we won't easily detect when the smart
>>> server is finished going this route.  As I at least wasn't seeing it
>>> disconnect from the fifo (echo foo > script, sends a POLLHUP event to
>>> select when the input is finished, I wasn't seeing that when lp-serve
>>> on the other side of a fifo finished.)
>> Ah, I see.
> 
> According to the poll(2) manpage and my rusty understanding, you get
> POLLHUP only when the remote end closes a socket you're trying to
> write to, and probably only if this causes you to lose
> already-buffered data.  If the client closes a socket you're trying to
> read from, I would expect you to get POLLIN and then find an EOF, or
> to get POLLRDHUP (which may not be exposed in Python.)
> 
> It's great to see this coming along.

Well, I *am* getting it when stdin finishes. I do have some code that
says "if event & POLLIN and not bytes" (if I got the POLLIN event but
there was no content) consider the connection closed. But I don't seem
to be getting that.

Which is also weird because 'cat /.../fifo' finishes correctly.

Anyway, ideally I wouldn't need the proxy in the middle, and just have
that done in the twisted code.

I'm still a little concerned about detecting process lifetimes and exit
codes (if they matter to twisted), since this process isn't a direct
child. Should I be trying to convey that information via another channel?

John
=:->
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