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Re: [PATCH 6/6] Retain caches of submodule refs

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Oct 9, 2011, 11:12 UTC
Message-ID
<4E918194.5060102@alum.mit.edu>
In-Reply-To
<7v4o1hgemp.fsf@alter.siamese.dyndns.org>
On 08/17/2011 12:45 AM, Junio C Hamano wrote:
> All the changes except for this one made sense to me, but I am not sure
> about this one. How often do we look into different submodule refs in the
> same process over and over again?
I am having pangs of uncertainty about this patch.

Previous to this patch, the submodule reference cache was only used for the duration of one call to do_for_each_ref(). (It was not *discarded* until later, but the old cache was never reused.) Therefore, the submodule reference cache was implicitly invalidated between successive uses.

After this change, submodule ref caches are invalidated whenever invalidate_cached_refs() is called. But this function is static, and it is only called when main-module refs are changed.

AFAIK there is no way within refs.c to add, modify, or delete a submodule reference. But if other code modifies submodule references directly, then the submodule ref cache in refs.c would become stale. Moreover, there is currently no API for invalidating the cache.

So I think I need help from a submodule guru (Heiko?) who can tell me what is done with submodule references and whether they might be modified while a git process is executing in the main module. If so, then either this patch has to be withdrawn, or more work has to be put in to make such code invalidate the submodule reference cache.

Sorry for the oversight, but I forgot that not all code necessarily uses the refs.c API when dealing with references (a regrettable situation, BTW).

Michael
-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/
Previous: Michael HaggertyNext: Junio C Hamano
Message 16 of 54 in “Retain caches of submodule refs”
  1. 0/6 Retain caches of submodule refsMichael Haggerty, Aug 12, 2011
  2. 1/6 Extract a function clear_cached_refs()Michael Haggerty, Aug 12, 2011
  3. 2/6 Access reference caches only through new function get_cached_refs().Michael Haggerty, Aug 12, 2011
  4. Junio C HamanoAug 14, 2011
  5. Michael HaggertyAug 23, 2011
  6. 3/6 Change the signature of read_packed_refs()Michael Haggerty, Aug 12, 2011
  7. 4/6 Allocate cached_refs objects dynamicallyMichael Haggerty, Aug 12, 2011
  8. Junio C HamanoAug 14, 2011
  9. 5/6 Store the submodule name in struct cached_refs.Michael Haggerty, Aug 12, 2011
  10. 6/6 Retain caches of submodule refsMichael Haggerty, Aug 12, 2011
  11. Heiko VoigtAug 13, 2011
  12. Michael HaggertyAug 24, 2011
  13. Heiko VoigtAug 24, 2011
  14. Junio C HamanoAug 16, 2011
  15. Michael HaggertyAug 24, 2011
  16. Michael HaggertyOct 9, 2011
  17. Junio C HamanoOct 9, 2011
  18. 0/2 Provide API to invalidate refs cacheMichael Haggerty, Oct 10, 2011
  19. 1/2 invalidate_cached_refs(): take the submodule as parameterMichael Haggerty, Oct 10, 2011
  20. 2/2 invalidate_cached_refs(): expose this function in refs APIMichael Haggerty, Oct 10, 2011
  21. 0/7 Provide API to invalidate refs cacheMichael Haggerty, Oct 10, 2011
  22. 1/7 invalidate_ref_cache(): rename function from invalidate_cached_refs()Michael Haggerty, Oct 10, 2011
  23. Junio C HamanoOct 11, 2011
  24. Michael HaggertyOct 11, 2011
  25. 2/7 invalidate_ref_cache(): take the submodule as parameterMichael Haggerty, Oct 10, 2011
  26. 3/7 invalidate_ref_cache(): expose this function in refs APIMichael Haggerty, Oct 10, 2011
  27. 4/7 clear_cached_refs(): rename parameterMichael Haggerty, Oct 10, 2011
  28. 5/7 clear_cached_refs(): extract two new functionsMichael Haggerty, Oct 10, 2011
  29. 6/7 write_ref_sha1(): only invalidate the loose ref cacheMichael Haggerty, Oct 10, 2011
  30. 7/7 clear_cached_refs(): inline functionMichael Haggerty, Oct 10, 2011
  31. Junio C HamanoOct 11, 2011
  32. Michael HaggertyOct 11, 2011
  33. Julian PhillipsOct 11, 2011
  34. Junio C HamanoOct 11, 2011
  35. 0/7 Provide API to invalidate refs cacheMichael Haggerty, Oct 12, 2011
  36. 1/7 invalidate_ref_cache(): rename function from invalidate_cached_refs()Michael Haggerty, Oct 12, 2011
  37. Junio C HamanoOct 12, 2011
  38. Michael HaggertyOct 12, 2011
  39. 2/7 invalidate_ref_cache(): take the submodule as parameterMichael Haggerty, Oct 12, 2011
  40. Junio C HamanoOct 12, 2011
  41. Michael HaggertyOct 12, 2011
  42. Junio C HamanoOct 17, 2011
  43. Michael HaggertyNov 3, 2011
  44. Junio C HamanoNov 3, 2011
  45. 3/7 invalidate_ref_cache(): expose this function in refs APIMichael Haggerty, Oct 12, 2011
  46. 4/7 clear_cached_refs(): rename parameterMichael Haggerty, Oct 12, 2011
  47. 5/7 clear_cached_refs(): extract two new functionsMichael Haggerty, Oct 12, 2011
  48. 6/7 write_ref_sha1(): only invalidate the loose ref cacheMichael Haggerty, Oct 12, 2011
  49. 7/7 clear_cached_refs(): inline functionMichael Haggerty, Oct 12, 2011
  50. Junio C HamanoOct 12, 2011
  51. Heiko VoigtOct 10, 2011
  52. Michael HaggertyOct 11, 2011
  53. Heiko VoigtOct 11, 2011
  54. Heiko VoigtAug 13, 2011

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