strbuf: avoid static variables in strbuf_add_commented_lines()

peff · gitster · commit 3b45450db65b · 2024-03-12T13:28:09.000-07:00
In strbuf_add_commented_lines(), we have to convert the single-byte
comment_line_char into a string to pass to add_lines(). We cache the
created string using a static-local variable. But this makes the
function non-reentrant, and it's doubtful that this provides any real
performance benefit given that we know the string always contains a
single character.

So let's just create it from scratch each time, and to give the compiler
the maximal opportunity to make it fast we'll ditch the over-complicated
xsnprintf() and just assign directly into the array.

Signed-off-by: Jeff King &lt;peff@peff.net&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/strbuf.c b/strbuf.c
@@ -361,10 +361,10 @@ static void add_lines(struct strbuf *out,
 void strbuf_add_commented_lines(struct strbuf *out, const char *buf,
 				size_t size, char comment_line_char)
 {
-	static char prefix[2];
+	char prefix[2];
 
-	if (prefix[0] != comment_line_char)
-		xsnprintf(prefix, sizeof(prefix), "%c", comment_line_char);
+	prefix[0] = comment_line_char;
+	prefix[1] = '\0';
 	add_lines(out, prefix, buf, size, 1);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -361,10 +361,10 @@ static void add_lines(struct strbuf *out,`
`361`	`361`	`void strbuf_add_commented_lines(struct strbuf out, const char buf,`
`362`	`362`	`size_t size, char comment_line_char)`
`363`	`363`	`{`
`364`		`- static char prefix[2];`
	`364`	`+ char prefix[2];`
`365`	`365`
`366`		`- if (prefix[0] != comment_line_char)`
`367`		`- xsnprintf(prefix, sizeof(prefix), "%c", comment_line_char);`
	`366`	`+ prefix[0] = comment_line_char;`
	`367`	`+ prefix[1] = '\0';`
`368`	`368`	`add_lines(out, prefix, buf, size, 1);`
`369`	`369`	`}`
`370`	`370`