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

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Jun 5, 2018, 23:16 UTC
Message-ID: <20180605231634.GD9266@aiede.svl.corp.google.com>
In-Reply-To: <c79a6e6f96e2e453017669fabbed1a9fb4036cce.1527894919.git.jonathantanmy@google.com>

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"?

> 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/

Show 6 quoted lines

> 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.

> The corresponding code for protocol v2 in process_acks() does not have
> the same problem, because the invoker of process_acks()
> (do_fetch_pack_v2()) proceeds immediately to processing the packfile

nit: s/proceeds/procedes/

Show 11 quoted lines

> upon "ACK %s ready". The clearing of rev_list here is thus redundant,
> and this patch also removes it.
>
> [1] The rationale is further described in the originating commit
> f2cba9299b ("fetch-pack: Finish negotation if remote replies "ACK %s
> ready"", 2011-03-14).
>
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
>  fetch-pack.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

[...]

Show 19 quoted lines

> +++ b/fetch-pack.c
> @@ -517,10 +517,8 @@ static int find_common(struct fetch_pack_args *args,
>  					mark_common(commit, 0, 1);
>  					retval = 0;
>  					got_continue = 1;
> -					if (ack == ACK_ready) {
> -						clear_prio_queue(&rev_list);
> +					if (ack == ACK_ready)
>  						got_ready = 1;
> -					}
>  					break;
>  					}
>  				}
> @@ -530,6 +528,8 @@ static int find_common(struct fetch_pack_args *args,
>  				print_verbose(args, _("giving up"));
>  				break; /* give up */
>  			}
> +			if (got_ready)
> +				break;

Makes sense.

Show 7 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?

Thanks, Jonathan