Can you suggest a sentence or two and the exact point where they should be inserted into the docs?
On Mon, Feb 24, 2014 at 10:39 AM, Christopher Probst < foxnet.develo...@googlemail.com> wrote: > Regarding the ENOBUFS issue: > > You are right, this info does not tell enough to use it for pause_writing. > And some BSD version drop packets silently if the queue is full. But on > Linux or Windows this technique is useful. Maybe a small annotation in the > docs could help for other users experiencing the same issue with BSD > systems. > > Am Montag, 24. Februar 2014 19:22:46 UTC+1 schrieb Guido van Rossum: >> >> Hm, so it sounds like the ENOBUFS error is intended as an improvement: it >> at least tells the caller that the packet was dropped immediately, which is >> a useful thing, even if the absence of that error does not constitute a >> guarantee. Unfortunately it doesn't look like we can use this directly to >> call pause_writing(), because there's no reliable way to tell that things >> are going to work again, except by trying. >> >> Regarding "reliable" UDP, I guess if you're really implementing TCP on >> top of UDP, you're not going to beat the performance of TCP. You're still >> going to need all the same AKCs etc. But don't let me stop you, I'm sure >> you have a good reason to do this. >> >> >> On Mon, Feb 24, 2014 at 12:49 AM, Christopher Probst < >> foxnet.d...@googlemail.com> wrote: >> >>> This is from FreeBSD mailing lists, it definitely says that sendto does >>> not block (select won't help, unfortunately it is like a file handle, it's >>> always writable). >>> http://lists.freebsd.org/pipermail/freebsd-hackers/ >>> 2004-January/005369.html >>> >>> Well, I think it is safe to say that tulips Datagram control-flow will >>> never really work on any BSD system. The sendto method simply never blocks. >>> It's also easy to explain the behavior you get: One mail says that >>> FreeBSD might drop packets, instead of raising ENOBUFS, so you get dramatic >>> packet loss instead of an error. >>> >>> >>> Am Montag, 24. Februar 2014 01:07:17 UTC+1 schrieb Guido van Rossum: >>>> >>>> "Reliable UDP"? Isn't that a contradiction? >>>> >>>> On Sunday, February 23, 2014, Christopher Probst < >>>> foxnet.d...@googlemail.com> wrote: >>>> >>>>> Thanks for your help so far, I really appreciate it. >>>>> >>>>> A manual backoff seems the best solution for this weird behavior for >>>>> now, since reliable udp heavily depends on timing this is not such a bad >>>>> thing anyway. >>>>> >>>>> Meanwhile I try to figure out the cause for this issue. >>>>> >>>>> >>>>> Am Montag, 24. Februar 2014 00:31:24 UTC+1 schrieb Guido van Rossum: >>>>>> >>>>>> I still can't repro it with your code. But that doesn't mean it's not >>>>>> a real condition. It sounds like the kind of odd corner of entirely >>>>>> legitimate UDP behavior that is hard to provoke but which a robust app >>>>>> should handle. >>>>>> >>>>>> Note that the default behavior in Tulip appears to be to ignore >>>>>> OSError coming out of sendto() -- the transport calls >>>>>> protocol.error_received(), which by default does nothing. Since there are >>>>>> many other cases where a packet may silently be dropped on the floor, >>>>>> this >>>>>> behavior is technically correct -- the question is whether it is the best >>>>>> default behavior we can imagine. >>>>>> >>>>>> Unfortunately turning it into a pause_protocol() call in your >>>>>> error_received() handler is a little tricky -- the transport remembers >>>>>> whether it has paused the protocol or not, but this state is not public. >>>>>> So >>>>>> you shouldn't call your own pause_writing(), since you'd never receive a >>>>>> resume_writing() call from the transport. Perhaps you can set a flag >>>>>> internal to your protocol that just causes you to back off for a brief >>>>>> period of time? The optimal back-off time should be tuned experimentally. >>>>>> >>>>>> --Guido >>>>>> >>>>>> On Sun, Feb 23, 2014 at 2:45 PM, Christopher Probst < >>>>>> foxnet.d...@googlemail.com> wrote: >>>>>> >>>>>> I made a simpler test, without using tulip, just using plain >>>>>> sockets<http://stackoverflow.com/questions/21973661/os-x-udp-send-error-55-no-buffer-space-available/21973705?noredirect=1#comment33297277_21973705> >>>>>> . >>>>>> >>>>>> from socket import * >>>>>> >>>>>> udp = socket(AF_INET, SOCK_DGRAM) >>>>>> udp.setsockopt(SOL_SOCKET, SO_REUSEADDR, True) >>>>>> >>>>>> udp.bind(('0.0.0.0', 1337)) >>>>>> udp.setblocking(False) >>>>>> udp.setsockopt(SOL_IP, IP_TTL, 4) >>>>>> udp.connect(('8.8.8.8 >>>>>> >>>>>> >>>> >>>> -- >>>> --Guido van Rossum (on iPad) >>>> >>> >> >> >> -- >> --Guido van Rossum (python.org/~guido) >> > -- --Guido van Rossum (python.org/~guido)
