From: Simon Ruderich <simon@ruderich.org>
Date: Tue, 8 Apr 2014 12:38:01 +0000 (+0200)
Subject: handle_recursive: fix race condition if threads are used
X-Git-Tag: 0.2~6
X-Git-Url: https://ruderich.org/simon/gitweb/?a=commitdiff_plain;h=b6d1dc09b620742b1877935f9f21a90a13ca5ee1;p=coloredstderr%2Fcoloredstderr.git

handle_recursive: fix race condition if threads are used

Requires thread-local storage.

Another solution would be a mutex, but this is slower and more
complicated and might cause issues with some programs.
---

diff --git a/NEWS b/NEWS
index 9c37519..b625510 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,8 @@ NEWS
 - Fix hook for GNU's error_at_line() not exiting if status != 0. If
   error_one_per_line was used and suppressed a message, then error_at_line()
   didn't exit.
+- Fix race condition when using threads. The fix requires thread-local
+  storage.
 
 
 0.1
diff --git a/configure.ac b/configure.ac
index e8d66a4..6ef50f4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -46,6 +46,7 @@ AC_TYPE_SSIZE_T
 
 AC_C_INLINE
 AX_C___ATTRIBUTE__
+AX_TLS
 
 AC_CHECK_MEMBER([struct _IO_FILE._fileno],
                 [AC_DEFINE([HAVE_STRUCT__IO_FILE__FILENO], 1,
diff --git a/m4/README b/m4/README
index 05e4069..bde2cea 100644
--- a/m4/README
+++ b/m4/README
@@ -7,3 +7,4 @@ The following files were copied unmodified from the autoconf archive [1]
 [1]: http://www.gnu.org/software/autoconf-archive/
 
 - ax_c___attribute__.m4
+- ax_tls.m4
diff --git a/m4/ax_tls.m4 b/m4/ax_tls.m4
new file mode 100644
index 0000000..033e3b1
--- /dev/null
+++ b/m4/ax_tls.m4
@@ -0,0 +1,76 @@
+# ===========================================================================
+#          http://www.gnu.org/software/autoconf-archive/ax_tls.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_TLS([action-if-found], [action-if-not-found])
+#
+# DESCRIPTION
+#
+#   Provides a test for the compiler support of thread local storage (TLS)
+#   extensions. Defines TLS if it is found. Currently knows about GCC/ICC
+#   and MSVC. I think SunPro uses the same as GCC, and Borland apparently
+#   supports either.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Alan Woodland <ajw05@aber.ac.uk>
+#   Copyright (c) 2010 Diego Elio Petteno` <flameeyes@gmail.com>
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 10
+
+AC_DEFUN([AX_TLS], [
+  AC_MSG_CHECKING(for thread local storage (TLS) class)
+  AC_CACHE_VAL(ac_cv_tls, [
+    ax_tls_keywords="__thread __declspec(thread) none"
+    for ax_tls_keyword in $ax_tls_keywords; do
+       AS_CASE([$ax_tls_keyword],
+          [none], [ac_cv_tls=none ; break],
+          [AC_TRY_COMPILE(
+              [#include <stdlib.h>
+               static void
+               foo(void) {
+               static ] $ax_tls_keyword [ int bar;
+               exit(1);
+               }],
+               [],
+               [ac_cv_tls=$ax_tls_keyword ; break],
+               ac_cv_tls=none
+           )])
+    done
+  ])
+  AC_MSG_RESULT($ac_cv_tls)
+
+  AS_IF([test "$ac_cv_tls" != "none"],
+    AC_DEFINE_UNQUOTED([TLS], $ac_cv_tls, [If the compiler supports a TLS storage class define it to that here])
+      m4_ifnblank([$1], [$1]),
+    m4_ifnblank([$2], [$2])
+  )
+])
diff --git a/src/coloredstderr.c b/src/coloredstderr.c
index c36e7d7..eaeebd3 100644
--- a/src/coloredstderr.c
+++ b/src/coloredstderr.c
@@ -30,6 +30,10 @@
 # define NDEBUG
 #endif
 
+#ifndef TLS
+# define TLS
+#endif
+
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -85,8 +89,8 @@ static int used_fds_set_by_user;
  * If so don't print the pre/post string for the recursive calls. This is
  * necessary on some systems (e.g. FreeBSD 9.1) which call multiple hooked
  * functions while printing a string (e.g. a FILE * and a fd hook function is
- * called). */
-static int handle_recursive;
+ * called). This is not thread-safe if TLS is not available. */
+static TLS int handle_recursive;
 
 
 #include "constants.h"