Subject: Re: [PATCH] prune: keep files created after process start

From: Junio C Hamano <[email-masked]>
Date: Sat, 18 Jun 2016 20:58:03 -0700

Eric Wong <[email-masked]> writes:

> Avoid pruning files which were written after the prune process
> starts, as it possible to concurrently create new objects while
> "git prune" is running.
>
> Tested on git.git by starting "git prune" in one terminal,
> creating a random loose object via "git hash-object --stdin -w"
> in a different terminal, and ensuring the loose object remains
> after "git prune" completes.
>
> Signed-off-by: Eric Wong <[email-masked]>
> ---
>  I'm somewhat surprised this check didn't already exist;
>  but maybe nobody else runs prune manually, anymore.

The only time an end user would run "git prune" in their
repositories with working trees these days is "git repack" followed
by "git prune", I would guess.

The current behaviour is totally expected and that is why you do not
run "prune" without any grace period in an active repository.

Adding the proposed change however would not make anything worse, I
would think.  Those who run "git prune" without grace period accept
that the repository must be quiescent or otherwise the newly created
objects will be lost.  So they are unlikely to be doing anything to
create such objects, hence "things newer than 'start'" are unlikely
to appear, and their expectation that "repack && prune" will remove
all loose objects will not be broken.

You generally cannot compare a timestamp you read from the
filesystem and the timestamp you obtain from time(2) when network
filesystems are involved, so I am not sure the implementation is
quite right, though.

> diff --git a/builtin/prune.c b/builtin/prune.c
> index 8f4f052..d4cd054 100644
> --- a/builtin/prune.c
> +++ b/builtin/prune.c
> @@ -14,6 +14,7 @@ static const char * const prune_usage[] = {
>  static int show_only;
>  static int verbose;
>  static unsigned long expire;
> +static time_t start;
>  static int show_progress = -1;
>  
>  static int prune_tmp_file(const char *fullpath)
> @@ -21,7 +22,7 @@ static int prune_tmp_file(const char *fullpath)
>  	struct stat st;
>  	if (lstat(fullpath, &st))
>  		return error("Could not stat '%s'", fullpath);
> -	if (st.st_mtime > expire)
> +	if (st.st_mtime > expire || st.st_ctime >= start)
>  		return 0;
>  	if (show_only || verbose)
>  		printf("Removing stale temporary file %s\n", fullpath);
> @@ -47,7 +48,7 @@ static int prune_object(const unsigned char *sha1, const char *fullpath,
>  		error("Could not stat '%s'", fullpath);
>  		return 0;
>  	}
> -	if (st.st_mtime > expire)
> +	if (st.st_mtime > expire || st.st_ctime >= start)
>  		return 0;
>  	if (show_only || verbose) {
>  		enum object_type type = sha1_object_info(sha1, NULL);
> @@ -111,6 +112,7 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
>  	};
>  	char *s;
>  
> +	start = time(NULL);
>  	expire = ULONG_MAX;
>  	save_commit_buffer = 0;
>  	check_replace_refs = 0;