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Re: [PATCH 1/2] diff: add an API for deferred freeing

From
Johannes Schindelin <johannes.schindelin@gmx.de>
Date
Feb 10, 2021, 16:00 UTC
Message-ID
<nycvar.QRO.7.76.6.2102101557160.29765@tvgsbejvaqbjf.bet>
In-Reply-To
<20210205141320.18076-1-avarab@gmail.com>
Hi Ævar,
On Fri, 5 Feb 2021, Ævar Arnfjörð Bjarmason wrote:
> Add a diff_free() function to free anything we may have allocated in
> the "diff_options" struct, and the ability to make calling it a noop
> by setting "no_free" in "diff_options".

Why do we need a `no_free` flag? Why not simply set the `free()`d (or `fclose()`d) attributes to `NULL`?

Show 19 quoted lines
> This is required because when e.g. "git diff" is run we'll allocate
> things in that struct, use the diff machinery once, and then exit, but
> if we run e.g. "git log -p" we're going to re-use what we allocated
> across multiple diff_flush() calls, and only want to free things at
> the end.
>
> We've thus ended up with features like the recently added "diff -I"[1]
> where we'll leak memory. As it turns out it could have simply used the
> pattern established in 6ea57703f6 (log: prepare log/log-tree to reuse
> the diffopt.close_file attribute, 2016-06-22).
>
> Manually adding more such flags to things log_tree_commit() every time
> we need to allocate something would be tedious.
>
> Let's instead move that fclose() code it to a new diff_free(), in
> anticipation of freeing more things in that function in follow-up
> commits. I'm renaming the "close_file" struct member to "fclose_file"
> for the ease of validating this, we can be certain that these are all
> the relevant callsites.
I like that idea a lot.
Show 30 quoted lines
> Some functions such as log_tree_commit() need an idiom of optionally
> retaining a previous "no_free", as they may either free the memory
> themselves, or their caller may do so. I'm keeping that idiom in
> log_show_early() even though I don't think it's currently called in
> this manner, since it also gets passed an existing "struct rev_info"..
>
> 1. 296d4a94e7 (diff: add -I<regex> that ignores matching changes,
>    2020-10-20)
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  builtin/add.c |  2 +-
>  builtin/am.c  |  6 ++++--
>  builtin/log.c | 27 ++++++++++++++-------------
>  diff.c        | 18 +++++++++++++-----
>  diff.h        | 14 +++++++++++++-
>  log-tree.c    | 10 ++++++----
>  wt-status.c   |  2 +-
>  7 files changed, 52 insertions(+), 27 deletions(-)
>
> diff --git a/builtin/add.c b/builtin/add.c
> index a825887c50..6319710186 100644
> --- a/builtin/add.c
> +++ b/builtin/add.c
> @@ -282,7 +282,7 @@ static int edit_patch(int argc, const char **argv, const char *prefix)
>  	if (out < 0)
>  		die(_("Could not open '%s' for writing."), file);
>  	rev.diffopt.file = xfdopen(out, "w");
> -	rev.diffopt.close_file = 1;
> +	rev.diffopt.fclose_file = 1;

This rename makes the patch unnecessarily tedious to review, and I do not even agree with leaking the implementation detail that we need to `fclose()` the file.

Let's just not?
Show 141 quoted lines
>  	if (run_diff_files(&rev, 0))
>  		die(_("Could not write patch"));
>
> diff --git a/builtin/am.c b/builtin/am.c
> index 8355e3566f..157d264583 100644
> --- a/builtin/am.c
> +++ b/builtin/am.c
> @@ -1315,7 +1315,7 @@ static void write_commit_patch(const struct am_state *state, struct commit *comm
>  	rev_info.diffopt.flags.full_index = 1;
>  	rev_info.diffopt.use_color = 0;
>  	rev_info.diffopt.file = fp;
> -	rev_info.diffopt.close_file = 1;
> +	rev_info.diffopt.fclose_file = 1; /* log_tree_commit() sets .no_free=1 */
>  	add_pending_object(&rev_info, &commit->object, "");
>  	diff_setup_done(&rev_info.diffopt);
>  	log_tree_commit(&rev_info, commit);
> @@ -1347,10 +1347,12 @@ static void write_index_patch(const struct am_state *state)
>  	rev_info.diffopt.output_format = DIFF_FORMAT_PATCH;
>  	rev_info.diffopt.use_color = 0;
>  	rev_info.diffopt.file = fp;
> -	rev_info.diffopt.close_file = 1;
> +	rev_info.diffopt.fclose_file = 1;
> +	rev_info.diffopt.no_free = 1;
>  	add_pending_object(&rev_info, &tree->object, "");
>  	diff_setup_done(&rev_info.diffopt);
>  	run_diff_index(&rev_info, 1);
> +	diff_free(&rev_info.diffopt);
>  }
>
>  /**
> diff --git a/builtin/log.c b/builtin/log.c
> index fd282def43..604ee29ec0 100644
> --- a/builtin/log.c
> +++ b/builtin/log.c
> @@ -306,10 +306,11 @@ static struct itimerval early_output_timer;
>
>  static void log_show_early(struct rev_info *revs, struct commit_list *list)
>  {
> -	int i = revs->early_output, close_file = revs->diffopt.close_file;
> +	int i = revs->early_output;
>  	int show_header = 1;
> +	int no_free = revs->diffopt.no_free;
>
> -	revs->diffopt.close_file = 0;
> +	revs->diffopt.no_free = 0;
>  	sort_in_topological_order(&list, revs->sort_order);
>  	while (list && i) {
>  		struct commit *commit = list->item;
> @@ -326,8 +327,8 @@ static void log_show_early(struct rev_info *revs, struct commit_list *list)
>  		case commit_ignore:
>  			break;
>  		case commit_error:
> -			if (close_file)
> -				fclose(revs->diffopt.file);
> +			revs->diffopt.no_free = no_free;
> +			diff_free(&revs->diffopt);
>  			return;
>  		}
>  		list = list->next;
> @@ -335,8 +336,8 @@ static void log_show_early(struct rev_info *revs, struct commit_list *list)
>
>  	/* Did we already get enough commits for the early output? */
>  	if (!i) {
> -		if (close_file)
> -			fclose(revs->diffopt.file);
> +		revs->diffopt.no_free = 0;
> +		diff_free(&revs->diffopt);
>  		return;
>  	}
>
> @@ -400,7 +401,7 @@ static int cmd_log_walk(struct rev_info *rev)
>  {
>  	struct commit *commit;
>  	int saved_nrl = 0;
> -	int saved_dcctc = 0, close_file = rev->diffopt.close_file;
> +	int saved_dcctc = 0;
>
>  	if (rev->early_output)
>  		setup_early_output();
> @@ -416,7 +417,7 @@ static int cmd_log_walk(struct rev_info *rev)
>  	 * and HAS_CHANGES being accumulated in rev->diffopt, so be careful to
>  	 * retain that state information if replacing rev->diffopt in this loop
>  	 */
> -	rev->diffopt.close_file = 0;
> +	rev->diffopt.no_free = 1;
>  	while ((commit = get_revision(rev)) != NULL) {
>  		if (!log_tree_commit(rev, commit) && rev->max_count >= 0)
>  			/*
> @@ -441,8 +442,8 @@ static int cmd_log_walk(struct rev_info *rev)
>  	}
>  	rev->diffopt.degraded_cc_to_c = saved_dcctc;
>  	rev->diffopt.needed_rename_limit = saved_nrl;
> -	if (close_file)
> -		fclose(rev->diffopt.file);
> +	rev->diffopt.no_free = 0;
> +	diff_free(&rev->diffopt);
>
>  	if (rev->diffopt.output_format & DIFF_FORMAT_CHECKDIFF &&
>  	    rev->diffopt.flags.check_failed) {
> @@ -1952,18 +1953,18 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
>  	if (rev.show_notes)
>  		load_display_notes(&rev.notes_opt);
>
> -	if (use_stdout + rev.diffopt.close_file + !!output_directory > 1)
> +	if (use_stdout + rev.diffopt.fclose_file + !!output_directory > 1)
>  		die(_("--stdout, --output, and --output-directory are mutually exclusive"));
>
>  	if (use_stdout) {
>  		setup_pager();
> -	} else if (rev.diffopt.close_file) {
> +	} else if (rev.diffopt.fclose_file) {
>  		/*
>  		 * The diff code parsed --output; it has already opened the
>  		 * file, but but we must instruct it not to close after each
>  		 * diff.
>  		 */
> -		rev.diffopt.close_file = 0;
> +		rev.diffopt.no_free = 1;
>  	} else {
>  		int saved;
>
> diff --git a/diff.c b/diff.c
> index 69e3bc00ed..3e6f8f0a71 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -5187,7 +5187,7 @@ static enum parse_opt_result diff_opt_output(struct parse_opt_ctx_t *ctx,
>  	BUG_ON_OPT_NEG(unset);
>  	path = prefix_filename(ctx->prefix, arg);
>  	options->file = xfopen(path, "w");
> -	options->close_file = 1;
> +	options->fclose_file = 1;
>  	if (options->use_color != GIT_COLOR_ALWAYS)
>  		options->use_color = GIT_COLOR_NEVER;
>  	free(path);
> @@ -6399,10 +6399,10 @@ void diff_flush(struct diff_options *options)
>  		 * options->file to /dev/null should be safe, because we
>  		 * aren't supposed to produce any output anyway.
>  		 */
> -		if (options->close_file)
> +		if (options->fclose_file)
>  			fclose(options->file);
And at this stage, we should set `options->file = NULL`.
Show 26 quoted lines
>  		options->file = xfopen("/dev/null", "w");
> -		options->close_file = 1;
> +		options->fclose_file = 1;
>  		options->color_moved = 0;
>  		for (i = 0; i < q->nr; i++) {
>  			struct diff_filepair *p = q->queue[i];
> @@ -6433,8 +6433,7 @@ void diff_flush(struct diff_options *options)
>  free_queue:
>  	free(q->queue);
>  	DIFF_QUEUE_CLEAR(q);
> -	if (options->close_file)
> -		fclose(options->file);
> +	diff_free(options);
>
>  	/*
>  	 * Report the content-level differences with HAS_CHANGES;
> @@ -6449,6 +6448,15 @@ void diff_flush(struct diff_options *options)
>  	}
>  }
>
> +void diff_free(struct diff_options *options)
> +{
> +	if (options->no_free)
> +		return;
> +	if (options->fclose_file)
> +		fclose(options->file);
And at this stage, we should set `options->file = NULL`.
Show 18 quoted lines
> +}
> +
> +
>  static int match_filter(const struct diff_options *options, const struct diff_filepair *p)
>  {
>  	return (((p->status == DIFF_STATUS_MODIFIED) &&
> diff --git a/diff.h b/diff.h
> index 2ff2b1c7f2..d1d74c3a9e 100644
> --- a/diff.h
> +++ b/diff.h
> @@ -49,7 +49,16 @@
>   * - Once you finish feeding the pairs of files, call `diffcore_std()`.
>   * This will tell the diffcore library to go ahead and do its work.
>   *
> + * - The `diff_opt_parse()` etc. functions might allocate memory in
> + *  `struct diff_options`. When running the API `N > 1` set `.no_free
> + *  = 1` to make the `diff_free()` invoked by `diff_flush()` below a
> + *  noop.

I have serious trouble parsing that last sentence. Would you mind rephrasing it?

Show 6 quoted lines
> + *
>   * - Calling `diff_flush()` will produce the output.
> + *
> + * - If you set `.no_free = 1` before set it to `0` and call
> + *   `diff_free()` again. If `.no_free = 1` was not set there's no
> + *   need to call `diff_free()`, `diff_flush()` will call it.

Again, as I mentioned before, the indicator whether things need to be released should be whether the attribute is `NULL` or not. And once released, ot should be set to `NULL`.

Other than that, it looks fine to me. And I definitely like the idea of introducing a function to release all of the stuff in `struct diffopt`.

Thanks, Dscho

Show 77 quoted lines
>   */
>
>  struct combine_diff_path;
> @@ -328,7 +337,7 @@ struct diff_options {
>  	void (*set_default)(struct diff_options *);
>
>  	FILE *file;
> -	int close_file;
> +	int fclose_file;
>
>  #define OUTPUT_INDICATOR_NEW 0
>  #define OUTPUT_INDICATOR_OLD 1
> @@ -365,6 +374,8 @@ struct diff_options {
>
>  	struct repository *repo;
>  	struct option *parseopts;
> +
> +	int no_free;
>  };
>
>  unsigned diff_filter_bit(char status);
> @@ -559,6 +570,7 @@ void diffcore_fix_diff_index(void);
>
>  int diff_queue_is_empty(void);
>  void diff_flush(struct diff_options*);
> +void diff_free(struct diff_options*);
>  void diff_warn_rename_limit(const char *varname, int needed, int degraded_cc);
>
>  /* diff-raw status letters */
> diff --git a/log-tree.c b/log-tree.c
> index fd0dde97ec..bb946f15f1 100644
> --- a/log-tree.c
> +++ b/log-tree.c
> @@ -952,12 +952,14 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
>  int log_tree_commit(struct rev_info *opt, struct commit *commit)
>  {
>  	struct log_info log;
> -	int shown, close_file = opt->diffopt.close_file;
> +	int shown;
> +	/* maybe called by e.g. cmd_log_walk(), maybe stand-alone */
> +	int no_free = opt->diffopt.no_free;
>
>  	log.commit = commit;
>  	log.parent = NULL;
>  	opt->loginfo = &log;
> -	opt->diffopt.close_file = 0;
> +	opt->diffopt.no_free = 1;
>
>  	if (opt->line_level_traverse)
>  		return line_log_print(opt, commit);
> @@ -974,7 +976,7 @@ int log_tree_commit(struct rev_info *opt, struct commit *commit)
>  		fprintf(opt->diffopt.file, "\n%s\n", opt->break_bar);
>  	opt->loginfo = NULL;
>  	maybe_flush_or_die(opt->diffopt.file, "stdout");
> -	if (close_file)
> -		fclose(opt->diffopt.file);
> +	opt->diffopt.no_free = no_free;
> +	diff_free(&opt->diffopt);
>  	return shown;
>  }
> diff --git a/wt-status.c b/wt-status.c
> index 0c8287a023..41b08474e5 100644
> --- a/wt-status.c
> +++ b/wt-status.c
> @@ -1052,7 +1052,7 @@ static void wt_longstatus_print_verbose(struct wt_status *s)
>  	rev.diffopt.rename_limit = s->rename_limit >= 0 ? s->rename_limit : rev.diffopt.rename_limit;
>  	rev.diffopt.rename_score = s->rename_score >= 0 ? s->rename_score : rev.diffopt.rename_score;
>  	rev.diffopt.file = s->fp;
> -	rev.diffopt.close_file = 0;
> +	rev.diffopt.fclose_file = 0; /* wt_status owns the s->fp */
>  	/*
>  	 * If we're not going to stdout, then we definitely don't
>  	 * want color, since we are going to the commit message
> --
> 2.30.0.284.gd98b1dd5eaa7
>
>
Previous: Ævar Arnfjörð BjarmasonNext: Ævar Arnfjörð Bjarmason
Message 50 of 57 in “diff: add -I<regex> that ignores matching changes”
  1. 0/2 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 1, 2020
  2. 2/2 t: add -I<regex> testsMichał Kępień, Oct 1, 2020
  3. 1/2 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 1, 2020
  4. Junio C HamanoOct 1, 2020
  5. Michał KępieńOct 7, 2020
  6. Junio C HamanoOct 7, 2020
  7. Junio C HamanoOct 1, 2020
  8. 0/3 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 12, 2020
  9. 1/3 merge-base, xdiff: zero out xpparam_t structuresMichał Kępień, Oct 12, 2020
  10. Johannes SchindelinOct 12, 2020
  11. Junio C HamanoOct 12, 2020
  12. Junio C HamanoOct 12, 2020
  13. Michał KępieńOct 13, 2020
  14. 2/3 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 12, 2020
  15. Johannes SchindelinOct 12, 2020
  16. Junio C HamanoOct 12, 2020
  17. Johannes SchindelinOct 12, 2020
  18. Junio C HamanoOct 12, 2020
  19. Michał KępieńOct 13, 2020
  20. Junio C HamanoOct 13, 2020
  21. Michał KępieńOct 13, 2020
  22. Johannes SchindelinOct 13, 2020
  23. Junio C HamanoOct 13, 2020
  24. Michał KępieńOct 13, 2020
  25. Junio C HamanoOct 12, 2020
  26. Michał KępieńOct 13, 2020
  27. Junio C HamanoOct 12, 2020
  28. Michał KępieńOct 13, 2020
  29. 3/3 t: add -I<regex> testsMichał Kępień, Oct 12, 2020
  30. Johannes SchindelinOct 12, 2020
  31. Michał KępieńOct 13, 2020
  32. Johannes SchindelinOct 13, 2020
  33. Junio C HamanoOct 13, 2020
  34. Michał KępieńOct 13, 2020
  35. Johannes SchindelinOct 15, 2020
  36. 0/2 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 15, 2020
  37. 1/2 merge-base, xdiff: zero out xpparam_t structuresMichał Kępień, Oct 15, 2020
  38. 2/2 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 15, 2020
  39. Phillip WoodOct 16, 2020
  40. Junio C HamanoOct 16, 2020
  41. Michał KępieńOct 19, 2020
  42. Junio C HamanoOct 16, 2020
  43. Michał KępieńOct 19, 2020
  44. Junio C HamanoOct 19, 2020
  45. Johannes SchindelinOct 16, 2020
  46. 0/2 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 20, 2020
  47. 1/2 merge-base, xdiff: zero out xpparam_t structuresMichał Kępień, Oct 20, 2020
  48. 2/2 diff: add -I<regex> that ignores matching changesMichał Kępień, Oct 20, 2020
  49. 1/2 diff: add an API for deferred freeingÆvar Arnfjörð Bjarmason, Feb 5, 2021
  50. Johannes SchindelinFeb 10, 2021
  51. Ævar Arnfjörð BjarmasonFeb 11, 2021
  52. Johannes SchindelinFeb 11, 2021
  53. Jeff KingFeb 11, 2021
  54. 2/2 diff: plug memory leak from regcomp() on {log,diff} -IÆvar Arnfjörð Bjarmason, Feb 11, 2021
  55. 0/2 diff: add an API for deferred freeingÆvar Arnfjörð Bjarmason, Feb 11, 2021
  56. 1/2 diff: add an API for deferred freeingÆvar Arnfjörð Bjarmason, Feb 11, 2021
  57. 2/2 diff: plug memory leak from regcomp() on {log,diff} -IÆvar Arnfjörð Bjarmason, Feb 5, 2021

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