[RFC][PATCH] grep: enable threading for context line printing

["René Scharfe" <rene.scharfe@lsrfire.ath.cx>]

This patch makes work_done() in builtin/grep.c print hunk marks between
files if threading is used, while show_line() in grep.c still does the
same in the other case.  The latter is  controlled by the struct grep_opt
member show_hunk_mark: 0 means show_line() prints no hunk marks between
files, 1 means it prints them before the next file with matches and 2
means it prints them before matches from the current file.

Having two places for this is a bit ugly but it enables parallel grep
for the common -ABC options.  Locking should be fine in add_work().

Comments?

René

---
 builtin/grep.c |   17 ++++++++++++++++-
 grep.c         |   14 +++-----------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index 40b9a93..8d58bb9 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -96,6 +96,9 @@ static pthread_cond_t cond_write;
 /* Signalled when we are finished with everything. */
 static pthread_cond_t cond_result;
 
+static int print_hunk_marks_between_files;
+static int printed_something;
+
 static void add_work(enum work_type type, char *name, void *id)
 {
 	grep_lock();
@@ -159,7 +162,12 @@ static void work_done(struct work_item *w)
 	for(; todo[todo_done].done && todo_done != todo_start;
 	    todo_done = (todo_done+1) % ARRAY_SIZE(todo)) {
 		w = &todo[todo_done];
-		write_or_die(1, w->out.buf, w->out.len);
+		if (w->out.len) {
+			if (print_hunk_marks_between_files && printed_something)
+				write_or_die(1, "--\n", 3);
+			write_or_die(1, w->out.buf, w->out.len);
+			printed_something = 1;
+		}
 		free(w->name);
 		free(w->identifier);
 	}
@@ -932,6 +940,13 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	use_threads = 0;
 #endif
 
+	if (opt.pre_context || opt.post_context) {
+		if (use_threads)
+			print_hunk_marks_between_files = 1;
+		else
+			opt.show_hunk_mark = 1;
+	}
+
 	compile_grep_patterns(&opt);
 
 	/* Check revs and then paths */
diff --git a/grep.c b/grep.c
index 90a063a..251c70c 100644
--- a/grep.c
+++ b/grep.c
@@ -549,10 +549,10 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 	sign_str[0] = sign;
 	if (opt->pre_context || opt->post_context) {
 		if (opt->last_shown == 0) {
-			if (opt->show_hunk_mark)
+			if (opt->show_hunk_mark == 2)
 				opt->output(opt, "--\n", 3);
-			else
-				opt->show_hunk_mark = 1;
+			else if (opt->show_hunk_mark == 1)
+				opt->show_hunk_mark = 2;
 		} else if (lno > opt->last_shown + 1)
 			opt->output(opt, "--\n", 3);
 	}
@@ -750,14 +750,6 @@ int grep_threads_ok(const struct grep_opt *opt)
 	    !opt->name_only)
 		return 0;
 
-	/* If we are showing hunk marks, we should not do it for the
-	 * first match. The synchronization problem we get for this
-	 * constraint is not yet solved, so we disable threading in
-	 * this case.
-	 */
-	if (opt->pre_context || opt->post_context)
-		return 0;
-
 	return 1;
 }