1 files changed, 67 insertions, 0 deletions
diff --git a/builtin-log.c b/builtin-log.c
index 8b2bf632c5..4e9d0cb69c 100644
--- a/builtin-log.c
+++ b/builtin-log.c
@@ -77,11 +77,78 @@ static void cmd_log_init(int argc, const char **argv, const char *prefix,
 	}
 }
 
+static void log_show_early(struct rev_info *revs, struct commit_list *list)
+{
+	int i = revs->early_output;
+
+	sort_in_topological_order(&list, revs->lifo);
+	while (list && i) {
+		struct commit *commit = list->item;
+		log_tree_commit(revs, commit);
+		list = list->next;
+		i--;
+	}
+}
+
+static void early_output(int signal)
+{
+	show_early_output = log_show_early;
+}
+
+static void setup_early_output(struct rev_info *rev)
+{
+	struct sigaction sa;
+	struct itimerval v;
+
+	/*
+	 * Set up the signal handler, minimally intrusively:
+	 * we only set a single volatile integer word (not
+	 * using sigatomic_t - trying to avoid unnecessary
+	 * system dependencies and headers), and using
+	 * SA_RESTART.
+	 */
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = early_output;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = SA_RESTART;
+	sigaction(SIGALRM, &sa, NULL);
+
+	/*
+	 * If we can get the whole output in less than a
+	 * tenth of a second, don't even bother doing the
+	 * early-output thing..
+	 *
+	 * This is a one-time-only trigger.
+	 */
+	memset(&v, 0, sizeof(v));
+	v.it_value.tv_sec = 0;
+	v.it_value.tv_usec = 100000;
+	setitimer(ITIMER_REAL, &v, NULL);
+}
+
+static void finish_early_output(struct rev_info *rev)
+{
+	signal(SIGALRM, SIG_IGN);
+	if (rev->shown_one) {
+		rev->shown_one = 0;
+		if (rev->commit_format != CMIT_FMT_ONELINE)
+			putchar(rev->diffopt.line_termination);
+	}
+	printf("Final output:\n");
+}
+
 static int cmd_log_walk(struct rev_info *rev)
 {
 	struct commit *commit;
 
+	if (rev->early_output)
+		setup_early_output(rev);
+
 	prepare_revision_walk(rev);
+
+	if (rev->early_output)
+		finish_early_output(rev);
+
 	while ((commit = get_revision(rev)) != NULL) {
 		log_tree_commit(rev, commit);
 		if (!rev->reflog_info) {