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From cbe8d2bcdc20682464217856aa48628804637f28 Mon Sep 17 00:00:00 2001
From: Bart Schaefer <schaefer@zsh.org>
Date: Thu, 28 Apr 2022 21:06:51 -0700
Subject: [PATCH] 50133: use read-ahead and lseek-rewind for efficient
line-buffered input
---
ChangeLog | 6 ++++++
Src/input.c | 24 ++++++++++++++++++++-
configure.ac | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 88 insertions(+), 1 deletion(-)
diff --git a/ChangeLog b/ChangeLog
index cae2fc4e3..79c77741b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2022-04-28 Bart Schaefer <schaefer@zsh.org>
+
+ * 50133 (Bart, PWS, Jun-ichi): Src/input.c, configure.ac: when
+ lseek(2) is available, use it to check for and rewind read-ahead
+ for more efficient line-buffered input.
+
2022-03-03 Peter Stephenson <p.w.stephenson@ntlworld.com>
* 49792: Src/input.c, Test/A01grammar.ztst: Use line buffering
diff --git a/Src/input.c b/Src/input.c
index caa8e23b0..6cc1b8a51 100644
--- a/Src/input.c
+++ b/Src/input.c
@@ -217,12 +217,34 @@ shinbufrestore(void)
static int
shingetchar(void)
{
- int nread;
+ int nread, rsize = isset(SHINSTDIN) ? 1 : SHINBUFSIZE;
if (shinbufptr < shinbufendptr)
return STOUC(*shinbufptr++);
shinbufreset();
+#ifdef USE_LSEEK
+ if (rsize == 1 && lseek(SHIN, 0, SEEK_CUR) != (off_t)-1)
+ rsize = SHINBUFSIZE;
+ if (rsize > 1) {
+ do {
+ errno = 0;
+ nread = read(SHIN, shinbuffer, rsize);
+ } while (nread < 0 && errno == EINTR);
+ if (nread <= 0)
+ return -1;
+ if (isset(SHINSTDIN) &&
+ (shinbufendptr = memchr(shinbuffer, '\n', nread))) {
+ shinbufendptr++;
+ rsize = (shinbufendptr - shinbuffer);
+ if (nread > rsize &&
+ lseek(SHIN, -(nread - rsize), SEEK_CUR) < 0)
+ zerr("lseek(%d, %d): %e", SHIN, -(nread - rsize), errno);
+ } else
+ shinbufendptr = shinbuffer + nread;
+ return STOUC(*shinbufptr++);
+ }
+#endif
for (;;) {
errno = 0;
nread = read(SHIN, shinbufendptr, 1);
diff --git a/configure.ac b/configure.ac
index af8c5bba8..42f2837cd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2304,6 +2304,65 @@ if test x$zsh_cv_sys_fifo = xyes; then
AC_DEFINE(HAVE_FIFOS)
fi
+dnl -----------
+dnl check that lseek() correctly reports seekability.
+dnl -----------
+AC_CACHE_CHECK(if lseek() correctly reports seekability,
+zsh_cv_sys_lseek,
+[AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#include <stdio.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+int main() {
+ int pipefd[2], fd;
+ off_t ret;
+ char* tmpfile = "seekfiletest.tmp";
+ if ((fd = open(tmpfile, O_CREAT, S_IRUSR)) < 0) {
+ fprintf(stderr, "creating file failed\n");
+ return 1;
+ }
+ ret = lseek(fd, 0, SEEK_CUR);
+ close(fd);
+ unlink(tmpfile);
+ if (ret == (off_t)-1) {
+ fprintf(stderr, "lseek on regular file failed\n");
+ return 1;
+ }
+ if (pipe(pipefd) < 0) {
+ fprintf(stderr, "creating pipe failed\n");
+ return 1;
+ }
+ write(pipefd[1], "abcdefgh", 8);
+ ret = lseek(pipefd[0], 0, SEEK_CUR);
+ close(pipefd[0]);
+ close(pipefd[1]);
+ if (ret != (off_t)-1) {
+ fprintf(stderr, "lseek on pipe succeeded\n");
+ return 1;
+ }
+ if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
+ fprintf(stderr, "creating UNIX domain socket failed\n");
+ return 1;
+ }
+ ret = lseek(fd, 0, SEEK_CUR);
+ close(fd);
+ if (ret != (off_t)-1) {
+ fprintf(stderr, "lseek on UNIX domain socket succeeded\n");
+ return 1;
+ }
+ return 0;
+}
+]])],[zsh_cv_sys_lseek=yes],[zsh_cv_sys_lseek=no],[zsh_cv_sys_lseek=yes])
+])
+AH_TEMPLATE([USE_LSEEK],
+[Define to 1 if lseek() can be used for SHIN.])
+if test x$zsh_cv_sys_lseek = xyes; then
+ AC_DEFINE(USE_LSEEK)
+fi
+
dnl -----------
dnl test for whether link() works
dnl for instance, BeOS R4.51 doesn't support hard links yet
--
2.36.0
|
