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Re: [PATCHv3 02/13] xread: poll on non blocking fds

From
Jeff King <peff@peff.net>
Date
Sep 22, 2015, 19:49 UTC
Message-ID
<20150922194927.GA622@sigill.intra.peff.net>
In-Reply-To
<xmqqy4fy2q6o.fsf@gitster.mtv.corp.google.com>
On Tue, Sep 22, 2015 at 12:45:51PM -0700, Junio C Hamano wrote:
Show 16 quoted lines
> Jacob Keller <jacob.keller@gmail.com> writes:
> 
> > I don't think this patch actually changes behavior as it stands now. I
> > think Junio's suggestion does. Personally, I'd prefer some sort of
> > warning when you use xread and get EAGAIN or EWOULDBLOCK. I'd rather
> > see it somehow warn so that we can find the bug (since we really
> > really shouldn't be calling xread with a blocking socket, especially
> > if we have xread_noblock or similar as in this series.
> 
> One caveat is that the caller may not know in the first place.
> 
> The last time I checked the existing callers of xread(), there were
> a few that read from a file descriptor they did not open themselves
> (e.g. unpack-objects that read from standard input).  The invoker of
> these processes is free to do O_NONBLOCK their input stream for
> whatever reason.

Yeah. I do not think this is a bug at all; the user might have their reasons for handing off an O_NONBLOCK pipe. If we take xread() to mean "try to read from fd until we get a real error, some data, or an EOF", then it is perfectly reasonable to replace spinning on read() (which we do now) with a poll() for efficiency. The caller (and the user) does not have to care, and should not notice; the outcome will be the same.

-Peff
Previous: Junio C HamanoNext: Junio C Hamano
Message 10 of 48 in “[PATCHv3 00/13] fetch submodules in parallel and a preview on parallel "submodule update"”
  1. Stefan BellerSep 21, 2015
  2. 01/13 Sending "Fetching submodule <foo>" output to stderrStefan Beller, Sep 21, 2015
  3. Junio C HamanoSep 21, 2015
  4. 02/13 xread: poll on non blocking fdsStefan Beller, Sep 21, 2015
  5. Junio C HamanoSep 21, 2015
  6. Torsten BögershausenSep 22, 2015
  7. Jacob KellerSep 22, 2015
  8. Torsten BögershausenSep 22, 2015
  9. Junio C HamanoSep 22, 2015
  10. Jeff KingSep 22, 2015
  11. Junio C HamanoSep 22, 2015
  12. Stefan BellerSep 23, 2015
  13. Junio C HamanoSep 23, 2015
  14. Jeff KingSep 23, 2015
  15. Eric SunshineSep 21, 2015
  16. Junio C HamanoSep 22, 2015
  17. Stefan BellerSep 22, 2015
  18. Junio C HamanoSep 22, 2015
  19. Stefan BellerSep 22, 2015
  20. 03/13 xread_nonblock: add functionality to read from fds nonblockinglyStefan Beller, Sep 21, 2015
  21. Junio C HamanoSep 22, 2015
  22. Junio C HamanoSep 22, 2015
  23. Jacob KellerSep 22, 2015
  24. Jacob KellerSep 22, 2015
  25. Junio C HamanoSep 22, 2015
  26. 04/13 strbuf: add strbuf_read_once to read without blockingStefan Beller, Sep 21, 2015
  27. Junio C HamanoSep 22, 2015
  28. Jacob KellerSep 22, 2015
  29. 05/13 run-command: factor out return value computationStefan Beller, Sep 21, 2015
  30. Junio C HamanoSep 22, 2015
  31. 06/13 run-command: add an asynchronous parallel child processorStefan Beller, Sep 21, 2015
  32. Junio C HamanoSep 22, 2015
  33. Stefan BellerSep 22, 2015
  34. Junio C HamanoSep 22, 2015
  35. Stefan BellerSep 22, 2015
  36. Junio C HamanoSep 22, 2015
  37. Stefan BellerSep 22, 2015
  38. Junio C HamanoSep 22, 2015
  39. 07/13 fetch_populated_submodules: use new parallel job processingStefan Beller, Sep 21, 2015
  40. Junio C HamanoSep 22, 2015
  41. 08/13 submodules: allow parallel fetching, add tests and documentationStefan Beller, Sep 21, 2015
  42. 09/13 submodule config: keep update strategy aroundStefan Beller, Sep 21, 2015
  43. Eric SunshineSep 22, 2015
  44. Stefan BellerSep 22, 2015
  45. 10/13 git submodule update: cmd_update_recursiveStefan Beller, Sep 21, 2015
  46. 11/13 git submodule update: cmd_update_cloneStefan Beller, Sep 21, 2015
  47. 12/13 git submodule update: cmd_update_fetchStefan Beller, Sep 21, 2015
  48. 13/13 Rewrite submodule update in CStefan Beller, Sep 21, 2015

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