From: Bruno Haible <bruno@clisp.org>
Date: Mon, 20 Aug 2007 22:09:08 +0000 (+0000)
Subject: Optimization: no need to flush stdin if we can determine quickly that stdin's
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7042775894700f8be0e6bc2a5ff3c49fc77296bc;p=pspp

Optimization: no need to flush stdin if we can determine quickly that stdin's
input buffer is empty.
---

diff --git a/ChangeLog b/ChangeLog
index 8a81c4a932..9fd9405b32 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-08-19  Bruno Haible  <bruno@clisp.org>
+
+	* modules/closein (Depends-on): Add freadahead.
+	* lib/closein.c: Include freadahead.h.
+	(close_stdin): Skip the fseeko and fflush calls if freadahead(stdin)
+	is zero.
+
 2007-08-19  Bruno Haible  <bruno@clisp.org>
 
 	* modules/freadahead-tests: New file.
diff --git a/lib/closein.c b/lib/closein.c
index 4450d5bd8d..bca7711bae 100644
--- a/lib/closein.c
+++ b/lib/closein.c
@@ -32,6 +32,7 @@
 #include "closeout.h"
 #include "error.h"
 #include "exitfail.h"
+#include "freadahead.h"
 #include "quotearg.h"
 
 static const char *file_name;
@@ -80,10 +81,16 @@ close_stdin (void)
 {
   bool fail = false;
 
-  /* Only attempt flush if stdin is seekable, as fflush is entitled to
-     fail on non-seekable streams.  */
-  if (fseeko (stdin, 0, SEEK_CUR) == 0 && fflush (stdin) != 0)
-    fail = true;
+  /* There is no need to flush stdin if we can determine quickly that stdin's
+     input buffer is empty; in this case we know that if stdin is seekable,
+     fseeko (stdin, 0, SEEK_CUR) == lseek (0, 0, SEEK_CUR).  */
+  if (freadahead (stdin) > 0)
+    {
+      /* Only attempt flush if stdin is seekable, as fflush is entitled to
+	 fail on non-seekable streams.  */
+      if (fseeko (stdin, 0, SEEK_CUR) == 0 && fflush (stdin) != 0)
+	fail = true;
+    }
   if (close_stream (stdin) != 0)
     fail = true;
   if (fail)
diff --git a/modules/closein b/modules/closein
index fefeae3648..522a383d3e 100644
--- a/modules/closein
+++ b/modules/closein
@@ -8,6 +8,7 @@ m4/closein.m4
 
 Depends-on:
 closeout
+freadahead
 fflush
 stdbool