From: Nick Mathewson <nickm@torproject.org>
Date: Tue, 2 Mar 2010 22:00:06 +0000 (-0500)
Subject: Improve the speed of evbuffer_readln()
X-Git-Tag: release-2.0.5-beta~105
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=cc1600afefc0c30586b12d916bb2a98ecf2d727b;p=libevent

Improve the speed of evbuffer_readln()

This makes some cases of bench_http about 5% faster.

Our internal evbuffer_strpbrk() function was overly general (it tried
to handle all character sets when we only used it for "\r\n"), and
not very efficient (it called memchr once for each character in the
buffer until it found a \r or a \n).  It actually showed up in some
profiles for HTTP testing, since evbuffer_readln() calls it when doing
loose CRLF detection.  This patch replaces it with a faster
implementation.
---

diff --git a/buffer.c b/buffer.c
index 08b9cba9..7f9e1fae 100644
--- a/buffer.c
+++ b/buffer.c
@@ -1016,17 +1016,16 @@ evbuffer_strchr(struct evbuffer_ptr *it, const char chr)
 {
 	struct evbuffer_chain *chain = it->_internal.chain;
 	unsigned i = it->_internal.pos_in_chain;
-	int count = 0;
 	while (chain != NULL) {
 		char *buffer = (char *)chain->buffer + chain->misalign;
-		for (; i < chain->off; ++i, ++count) {
-			if (buffer[i] == chr) {
-				it->_internal.chain = chain;
-				it->_internal.pos_in_chain = i;
-				it->pos += count;
-				return (count);
-			}
+		char *cp = memchr(buffer+i, chr, chain->off-i);
+		if (cp) {
+			it->_internal.chain = chain;
+			it->_internal.pos_in_chain = cp - buffer;
+			it->pos += (cp - buffer);
+			return it->pos;
 		}
+		it->pos += chain->off - i;
 		i = 0;
 		chain = chain->next;
 	}
@@ -1034,25 +1033,48 @@ evbuffer_strchr(struct evbuffer_ptr *it, const char chr)
 	return (-1);
 }
 
-static inline int
-evbuffer_strpbrk(struct evbuffer_ptr *it, const char *chrset)
+static inline char *
+find_eol_char(char *s, size_t len)
+{
+#define CHUNK_SZ 128
+	/* Lots of benchmarking found this approach to be faster in practice
+	 * than doing two memchrs over the whole buffer, doin a memchr on each
+	 * char of the buffer, or trying to emulate memchr by hand. */
+	char *s_end, *cr, *lf;
+	s_end = s+len;
+	while (s < s_end) {
+		size_t chunk = (s + CHUNK_SZ < s_end) ? CHUNK_SZ : (s_end - s);
+		cr = memchr(s, '\r', chunk);
+		lf = memchr(s, '\n', chunk);
+		if (cr) {
+			if (lf && lf < cr)
+				return lf;
+			return cr;
+		} else if (lf) {
+			return lf;
+		}
+		s += CHUNK_SZ;
+	}
+
+	return NULL;
+#undef CHUNK_SZ
+}
+
+static int
+evbuffer_find_eol_char(struct evbuffer_ptr *it)
 {
 	struct evbuffer_chain *chain = it->_internal.chain;
 	unsigned i = it->_internal.pos_in_chain;
-	int count = 0;
 	while (chain != NULL) {
 		char *buffer = (char *)chain->buffer + chain->misalign;
-		for (; i < chain->off; ++i, ++count) {
-			const char *p = chrset;
-			while (*p) {
-				if (buffer[i] == *p++) {
-					it->_internal.chain = chain;
-					it->_internal.pos_in_chain = i;
-					it->pos += count;
-					return (count);
-				}
-			}
+		char *cp = find_eol_char(buffer+i, chain->off-i);
+		if (cp) {
+			it->_internal.chain = chain;
+			it->_internal.pos_in_chain = cp - buffer;
+			it->pos += (cp - buffer) - i;
+			return it->pos;
 		}
+		it->pos += chain->off - i;
 		i = 0;
 		chain = chain->next;
 	}
@@ -1132,7 +1154,7 @@ evbuffer_search_eol(struct evbuffer *buffer,
 	 * characters we are going to drain afterwards. */
 	switch (eol_style) {
 	case EVBUFFER_EOL_ANY:
-		if (evbuffer_strpbrk(&it, "\r\n") < 0)
+		if (evbuffer_find_eol_char(&it) < 0)
 			goto done;
 		memcpy(&it2, &it, sizeof(it));
 		extra_drain = evbuffer_strspn(&it2, "\r\n");
@@ -1146,7 +1168,7 @@ evbuffer_search_eol(struct evbuffer *buffer,
 	}
 	case EVBUFFER_EOL_CRLF:
 		while (1) {
-			if (evbuffer_strpbrk(&it, "\r\n") < 0)
+			if (evbuffer_find_eol_char(&it) < 0)
 				goto done;
 			if (evbuffer_getchr(&it) == '\n') {
 				extra_drain = 1;