Pádraig Brady wrote:
It would be nice to have areadlink_with_size treat 0 as auto select some lower
bound.
Yes, that sounds good. However, I didn't see why that would entail changing
SYMLINK_MAX from 1024 to 1023, or why the patch would affect the documented API.
How about the attached patch instead? When the guessed size is zero it typically
avoids a realloc by using a small stack buffer.
>From d94bf537d7fdda13f4432bb60a98a8bd19d8e18d Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Fri, 5 Jul 2019 16:48:22 -0700
Subject: [PATCH] areadlink-with-size: improve efficiency
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
If the guessed size is 0, guess 200 first, to avoid a sequence of
small readlinks in the usual case. Reallocate at the end to the
actual size, to avoid memory waste. Based on a suggestion by
Pádraig Brady.
* lib/areadlink-with-size.c (areadlink_with_size):
Use a small stack buffer when the stated size is zero.
* modules/areadlink-with-size (Depends-on): Add strdup-posix.
---
ChangeLog | 11 +++++++++++
lib/areadlink-with-size.c | 26 ++++++++++++++++++++------
modules/areadlink-with-size | 1 +
3 files changed, 32 insertions(+), 6 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 98d5531b1..b07e26335 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2019-07-05 Paul Eggert <egg...@cs.ucla.edu>
+
+ areadlink-with-size: improve efficiency
+ If the guessed size is 0, guess 200 first, to avoid a sequence of
+ small readlinks in the usual case. Reallocate at the end to the
+ actual size, to avoid memory waste. Based on a suggestion by
+ Pádraig Brady.
+ * lib/areadlink-with-size.c (areadlink_with_size):
+ Use a small stack buffer when the stated size is zero.
+ * modules/areadlink-with-size (Depends-on): Add strdup-posix.
+
2019-07-05 Bruno Haible <br...@clisp.org>
getcwd-lgpl, getcwd: Don't call realloc when it is pointless.
diff --git a/lib/areadlink-with-size.c b/lib/areadlink-with-size.c
index 364cc0858..9f1f7959f 100644
--- a/lib/areadlink-with-size.c
+++ b/lib/areadlink-with-size.c
@@ -60,18 +60,30 @@ areadlink_with_size (char const *file, size_t size)
? symlink_max + 1
: INITIAL_LIMIT_BOUND);
+ /* Size of stack buffer for initial readlink when the link size hint
+ is zero. */
+ enum { stackbuf_size = 200 };
+
/* The initial buffer size for the link value. */
- size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
+ size_t buf_size = (size == 0 ? stackbuf_size
+ : size < initial_limit ? size + 1 : initial_limit);
while (1)
{
ssize_t r;
size_t link_length;
- char *buffer = malloc (buf_size);
+ char stackbuf[stackbuf_size];
+ char *buf = stackbuf;
+ char *buffer = NULL;
+
+ if (! (size == 0 && buf_size == stackbuf_size))
+ {
+ buf = buffer = malloc (buf_size);
+ if (!buffer)
+ return NULL;
+ }
- if (buffer == NULL)
- return NULL;
- r = readlink (file, buffer, buf_size);
+ r = readlink (file, buf, buf_size);
link_length = r;
/* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
@@ -86,7 +98,9 @@ areadlink_with_size (char const *file, size_t size)
if (link_length < buf_size)
{
- buffer[link_length] = 0;
+ buf[link_length] = 0;
+ if (!buffer)
+ return strdup (buf);
/* Shrink BUFFER before returning it. */
if (link_length + 1 < buf_size)
{
diff --git a/modules/areadlink-with-size b/modules/areadlink-with-size
index 82a902187..a4ab0e178 100644
--- a/modules/areadlink-with-size
+++ b/modules/areadlink-with-size
@@ -9,6 +9,7 @@ Depends-on:
readlink
ssize_t
stdint
+strdup-posix
unistd
configure.ac:
--
2.17.1
