Re: [PATCH] gc --auto: do not lock refs in the background

> 9f673f9 (gc: config option for running --auto in background -
> 2014-02-08) puts "gc --auto" in background to reduce user's wait
> time. Part of the garbage collecting is pack-refs and pruning
> reflogs. These require locking some refs and may abort other processes
> trying to lock the same ref. If gc --auto is fired in the middle of a
> script, gc's holding locks in the background could fail the script,
> which could never happen before 9f673f9.
>
> Keep running pack-refs and "reflog --prune" in foreground to stop
> parallel ref updates. The remaining background operations (repack,
> prune and rerere) should impact running git processes.
>
> Reported-by: Adam Borowski <kilobyte@angband.pl>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  builtin/gc.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)

> diff --git a/builtin/gc.c b/builtin/gc.c
> index 85f5c2b..8d219d8 100644
> --- a/builtin/gc.c
> +++ b/builtin/gc.c
> @@ -26,6 +26,7 @@ static const char * const builtin_gc_usage[] = {
>  };
>  
>  static int pack_refs = 1;
> +static int prune_reflogs = 1;
>  static int aggressive_depth = 250;
>  static int aggressive_window = 250;
>  static int gc_auto_threshold = 6700;
> @@ -258,6 +259,19 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
>  	return NULL;
>  }
>  
> +static int gc_before_repack(void)
> +{
> +	if (pack_refs && run_command_v_opt(pack_refs_cmd.argv, RUN_GIT_CMD))
> +		return error(FAILED_RUN, pack_refs_cmd.argv[0]);
> +
> +	if (prune_reflogs && run_command_v_opt(reflog.argv, RUN_GIT_CMD))
> +		return error(FAILED_RUN, reflog.argv[0]);
> +
> +	pack_refs = 0;
> +	prune_reflogs = 0;
> +	return 0;
> +}
> +
>  int cmd_gc(int argc, const char **argv, const char *prefix)
>  {
>  	int aggressive = 0;
> @@ -320,12 +334,15 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
>  				fprintf(stderr, _("Auto packing the repository for optimum performance.\n"));
>  			fprintf(stderr, _("See \"git help gc\" for manual housekeeping.\n"));
>  		}
> -		if (detach_auto)
> +		if (detach_auto) {
> +			if (gc_before_repack())
> +				return -1;
>  			/*
>  			 * failure to daemonize is ok, we'll continue
>  			 * in foreground
>  			 */
>  			daemonize();
> +		}
>  	} else
>  		add_repack_all_option();
>  
> @@ -337,11 +354,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
>  		    name, (uintmax_t)pid);
>  	}
>  
> -	if (pack_refs && run_command_v_opt(pack_refs_cmd.argv, RUN_GIT_CMD))
> -		return error(FAILED_RUN, pack_refs_cmd.argv[0]);
> -
> -	if (run_command_v_opt(reflog.argv, RUN_GIT_CMD))
> -		return error(FAILED_RUN, reflog.argv[0]);
> +	if (gc_before_repack())
> +		return -1;
>  
>  	if (run_command_v_opt(repack.argv, RUN_GIT_CMD))
>  		return error(FAILED_RUN, repack.argv[0]);