Messages in this thread | | | Date | Fri, 12 May 2006 20:16:03 +0530 | From | jimmy <> | Subject | Re: Linux poll() <sigh> again |
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Robert Hancock wrote: > linux-os (Dick Johnson) wrote: >>> POLLHUP means "The device has been disconnected." This would obviously >>> be appropriate for a device such as a serial line or TTY, etc. but for a >>> socket it is less obvious that this return value is appropriate. >>> >> >> Hardly "less obvious". SunOs has returned POLLHUP as has other >> Unixes like Interactive, from which the software was ported. It >> went from Interactive, to SunOs, to Linux. Linux was the first >> OS that required the hack. This was reported several years ago >> and I was simply excoriated for having the audacity to report >> such a thing. So, I just implemented a hack. Now the hack is >> biting me. It's about time for poll() to return the correct >> stuff. > > The standard doesn't require that a close on a socket should report > POLLHUP. Thus this behavior may differ between UNIX implementations. If > your software is requiring a POLLHUP to indicate the socket is closed I > think it is being unnecessarily picky since read returning 0 universally > indicates that the connection has been closed. Such are the compromises > that are sometimes required to write portable software. > >> >>>> I have used the subsequent read() with a returned >>>> value of zero, to indicate that the client disconnected >>>> (as a work around). However, on recent versions of >>>> Linux, this is not reliable and the read() may >>>> wait forever instead of immediately returning. >>> If you want nonblocking behavior, you should set the socket to >>> nonblocking. This is a bit strange though, unless the data was stolen by >>> another thread or something. Are you sure you've seen this? >> >> I don't use threads. The hang under the specified conditions was first >> observed on 2.6.16.4 (that I'm running on this system). The hack, >> previously >> used, i.e., the read of zero was used since 2.4.x with success except >> it's >> a hack and shouldn't be required. It was not ever required on SunOs from >> which the software was ported. > > This may be a bug somewhere.. however, once again if you don't want read > to block under any circumstances, set your sockets to non-blocking! > But that's another hack. AFAICS why ppl (mostly) use select/poll wud be to know if their send/recv/read/write would go thru rather than getting blocked!
-jb -- Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. - Albert Einstein - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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