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Re: [PATCHv3 02/11] run-command: report failure for degraded output just once

From
Junio C Hamano <gitster@pobox.com>
Date
Nov 4, 2015, 21:01 UTC
Message-ID
<xmqq4mh1a37i.fsf@gitster.mtv.corp.google.com>
In-Reply-To
<563A6C3D.2050805@kdbg.org>
Johannes Sixt <j6t@kdbg.org> writes:
> I think that a scenario where A and B are communicating is rather
> far-fetched. We are talking about parallelizing independent tasks. I
> would not worry.

I wouldn't worry too much if this were merely a hack that is only applicable to submodules, but I do not think it is a healthy attitude to dismiss potential problem as far-fetched without thinking things through, when you are designing what goes into the run-command API.

I'd grant you that a complete deadlock is unlikely to be a problem on its own. Somewhere somebody will eventually time out and unblock the deadlock anyway.

But the symptom does not have to be as severe as a total deadlock to be problematic. If we block B (and other tasks) by not reading from them quickly because we are blocked on reading from A, which may take forever (in timescale of B and other tasks) to feed us enough to satisfy strbuf_read_once(), we are wasting resource by spawning B (and other tasks) early when we are not prepared to service them well, on both our end and on the other side of the connection.

By the way, A and B do not have to be directly communicating to deadlock. The underlying system, either the remote end or the local end or even a relaying system in between (think: network) can throttle to cause the same symptom without A and B knowing (which was the example I gave).

Previous: Johannes SixtNext: Jeff King
Message 7 of 34 in “[PATCHv3 00/11] Expose the submodule parallelism to the user”
  1. Stefan BellerNov 4, 2015
  2. 01/11 run_processes_parallel: delimit intermixed task outputStefan Beller, Nov 4, 2015
  3. 02/11 run-command: report failure for degraded output just onceStefan Beller, Nov 4, 2015
  4. Junio C HamanoNov 4, 2015
  5. Stefan BellerNov 4, 2015
  6. Johannes SixtNov 4, 2015
  7. Junio C HamanoNov 4, 2015
  8. Jeff KingNov 4, 2015
  9. Junio C HamanoNov 5, 2015
  10. Jeff KingNov 5, 2015
  11. Junio C HamanoNov 5, 2015
  12. Stefan BellerNov 5, 2015
  13. Junio C HamanoNov 4, 2015
  14. Stefan BellerNov 4, 2015
  15. Junio C HamanoNov 4, 2015
  16. Stefan BellerNov 4, 2015
  17. 03/11 run-command: omit setting file descriptors to non blocking in WindowsStefan Beller, Nov 4, 2015
  18. 04/11 submodule-config: keep update strategy aroundStefan Beller, Nov 4, 2015
  19. 05/11 submodule-config: drop check against NULLStefan Beller, Nov 4, 2015
  20. 06/11 submodule-config: remove name_and_item_from_varStefan Beller, Nov 4, 2015
  21. 07/11 submodule-config: introduce parse_generic_submodule_configStefan Beller, Nov 4, 2015
  22. 08/11 fetching submodules: respect `submodule.jobs` config optionStefan Beller, Nov 4, 2015
  23. Jens LehmannNov 10, 2015
  24. Stefan BellerNov 10, 2015
  25. Jens LehmannNov 11, 2015
  26. Stefan BellerNov 11, 2015
  27. Jens LehmannNov 13, 2015
  28. Stefan BellerNov 13, 2015
  29. 09/11 git submodule update: have a dedicated helper for cloningStefan Beller, Nov 4, 2015
  30. 10/11 submodule update: expose parallelism to the userStefan Beller, Nov 4, 2015
  31. 11/11 clone: allow an explicit argument for parallel submodule clonesStefan Beller, Nov 4, 2015
  32. Junio C HamanoNov 4, 2015
  33. Stefan BellerNov 4, 2015
  34. Junio C HamanoNov 4, 2015

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