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Re: [PATCH 2/6] fetch-pack: truly stop negotiation upon ACK ready

From
JTJonathan Tan <jonathantanmy@google.com>
Date
Jun 6, 2018, 00:38 UTC
Message-ID
<20180605173818.4d56cf328d81b29a2878c1f6@google.com>
In-Reply-To
<20180605231634.GD9266@aiede.svl.corp.google.com>

On Tue, 5 Jun 2018 16:16:34 -0700 Jonathan Nieder <jrnieder@gmail.com> wrote:

Show 10 quoted lines
> Hi,
> 
> Jonathan Tan wrote:
> 
> > When "ACK %s ready" is received, find_common() clears rev_list in an
> > attempt to stop further "have" lines from being sent [1]. This appears
> > to work, despite the invocation to mark_common() in the "while" loop.
> 
> Does "appears to work" mean "works" or "doesn't work but does an okay
> job of faking"?

"Appears to work" means I think that it works, but I don't think I can conclusively prove it.

Show 17 quoted lines
> > Though it is possible for mark_common() to invoke rev_list_push() (thus
> > making rev_list non-empty once more), it is more likely that the commits
> 
> nit: s/more likely/most likely/
> or s/it is more likely that/usually/
> 
> > in rev_list that have un-SEEN parents are also unparsed, meaning that
> > mark_common() is not invoked on them.
> >
> > To avoid all this uncertainty, it is better to explicitly end the loop
> > when "ACK %s ready" is received instead of clearing rev_list. Remove the
> > clearing of rev_list and write "if (got_ready) break;" instead.
> 
> I'm still a little curious about whether this can happen in practice
> or whether it's just about readability (or whether you didn't figure
> out which, which is perfectly fine), but either way it's a good
> change.
I tried to figure out which, but concluded that I can't.

I think that in v2's commit message, I'll start with describing the readability aspect.

Show 10 quoted lines
> > @@ -1281,7 +1281,6 @@ static int process_acks(struct packet_reader *reader, struct oidset *common)
> >  		}
> >  
> >  		if (!strcmp(reader->line, "ready")) {
> > -			clear_prio_queue(&rev_list);
> >  			received_ready = 1;
> >  			continue;
> 
> I'm curious about the lifetime of &rev_list.  Does the priority queue
> get freed eventually?

No (which potentially causes a problem in the case that fetch-pack is invoked twice), but I fix that in patch 4/6, so I didn't bother addressing it here. I'll add a note about the lifetime of this priority queue in v2.

Previous: Jonathan NiederNext: Jonathan Tan
Message 8 of 47 in “Refactor fetch negotiation into its own API”
  1. 0/6 Refactor fetch negotiation into its own APIJonathan Tan, Jun 4, 2018
  2. 1/6 fetch-pack: clear marks before everything_local()Jonathan Tan, Jun 4, 2018
  3. Jonathan NiederJun 5, 2018
  4. Jonathan TanJun 6, 2018
  5. 2/6 fetch-pack: truly stop negotiation upon ACK readyJonathan Tan, Jun 4, 2018
  6. Jonathan NiederJun 5, 2018
  7. Jonathan NiederJun 5, 2018
  8. Jonathan TanJun 6, 2018
  9. 3/6 fetch-pack: in protocol v2, enqueue commons firstJonathan Tan, Jun 4, 2018
  10. Jonathan NiederJun 5, 2018
  11. Jonathan TanJun 6, 2018
  12. 4/6 fetch-pack: make negotiation-related vars localJonathan Tan, Jun 4, 2018
  13. Jonathan NiederJun 5, 2018
  14. Jonathan TanJun 6, 2018
  15. 5/6 fetch-pack: move common check and marking togetherJonathan Tan, Jun 4, 2018
  16. Jonathan NiederJun 6, 2018
  17. Jonathan TanJun 6, 2018
  18. 6/6 fetch-pack: introduce negotiator APIJonathan Tan, Jun 4, 2018
  19. Jonathan NiederJun 6, 2018
  20. Jonathan TanJun 6, 2018
  21. 0/8 Refactor fetch negotiation into its own APIJonathan Tan, Jun 6, 2018
  22. 1/8 fetch-pack: split up everything_local()Jonathan Tan, Jun 6, 2018
  23. Brandon WilliamsJun 14, 2018
  24. 2/8 fetch-pack: clear marks before re-markingJonathan Tan, Jun 6, 2018
  25. 4/8 fetch-pack: use ref adv. to prune "have" sentJonathan Tan, Jun 6, 2018
  26. Brandon WilliamsJun 14, 2018
  27. Junio C HamanoJun 14, 2018
  28. 5/8 fetch-pack: make negotiation-related vars localJonathan Tan, Jun 6, 2018
  29. Brandon WilliamsJun 14, 2018
  30. Junio C HamanoJun 14, 2018
  31. 6/8 fetch-pack: move common check and marking togetherJonathan Tan, Jun 6, 2018
  32. 8/8 negotiator/default: use better style in commentsJonathan Tan, Jun 6, 2018
  33. Brandon WilliamsJun 14, 2018
  34. 7/8 fetch-pack: introduce negotiator APIJonathan Tan, Jun 6, 2018
  35. 3/8 fetch-pack: directly end negotiation if ACK readyJonathan Tan, Jun 6, 2018
  36. Brandon WilliamsJun 14, 2018
  37. Brandon WilliamsJun 14, 2018
  38. 0/7 Refactor fetch negotiation into its own APIJonathan Tan, Jun 14, 2018
  39. 1/7 fetch-pack: split up everything_local()Jonathan Tan, Jun 14, 2018
  40. 2/7 fetch-pack: clear marks before re-markingJonathan Tan, Jun 14, 2018
  41. 3/7 fetch-pack: directly end negotiation if ACK readyJonathan Tan, Jun 14, 2018
  42. Junio C HamanoJun 15, 2018
  43. 4/7 fetch-pack: use ref adv. to prune "have" sentJonathan Tan, Jun 14, 2018
  44. 5/7 fetch-pack: make negotiation-related vars localJonathan Tan, Jun 14, 2018
  45. 6/7 fetch-pack: move common check and marking togetherJonathan Tan, Jun 14, 2018
  46. 7/7 fetch-pack: introduce negotiator APIJonathan Tan, Jun 14, 2018
  47. Brandon WilliamsJun 25, 2018

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