Fix: tls-compat.h exposes compiler-dependent public configuration

Exposing the storage class chosen by ax_tls.m4 in a public header is
a bad idea, because if a recent gcc is used when configuring
liburcu, thus detecting C11, it will choose _Thread_local. Then, if an
external project uses urcu/tls-compat.h with an older gcc (e.g. 4.8),
it will fail to build, because that storage class is unknown, and
__thread should be used instead.

Therefore, use a preprocessor conditional on __cplusplus to detect C++11
(and use thread_local). Else, the STDC version is used to select
_Thread_local. Else check if _MSC_VER is defined to select
__declspec(thread), or else rely on __thread as fallback.

Remove ax_tls.m4 because it is now unused.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/configure.ac b/configure.ac
index a5a2ec272d62093c0e3add9ba46f4cbb2369f138..7dfc2f3505d3a98d4a4dcdc95c48bf34cebdbed1 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -33,14 +33,7 @@ AC_ARG_ENABLE([compiler-tls],
        [def_compiler_tls=$enableval],
        [def_compiler_tls="yes"])
 
-# If not overridden, use ax_tls.m4 to check if TLS is available.
-AS_IF([test "x$def_compiler_tls" = "xyes"],
-       [AX_TLS([def_tls_detect=$ac_cv_tls], [:])],
-       [:])
-
-AS_IF([test "x$def_tls_detect" = "x"],
-       [:],
-       [AC_DEFINE_UNQUOTED([CONFIG_RCU_TLS], $def_tls_detect)])
+AS_IF([test "x$def_compiler_tls" = "xyes"], AC_DEFINE([CONFIG_RCU_TLS], [1]), [:])
 
 # Checks for C compiler
 AC_USE_SYSTEM_EXTENSIONS
@@ -401,8 +394,8 @@ AS_IF([test "x$def_smp_support" = "xyes"],[
        AS_ECHO("SMP support disabled.")
 ])
 
-AS_IF([test "x$def_tls_detect" = "x"],[
-       AS_ECHO("Thread Local Storage (TLS): pthread_getspecific().")
+AS_IF([test "x$def_compiler_tls" = "xyes"],[
+       AS_ECHO("Thread Local Storage (TLS): compiler TLS.")
 ],[
-       AS_ECHO("Thread Local Storage (TLS): $def_tls_detect.")
+       AS_ECHO("Thread Local Storage (TLS): pthread_getspecific().")
 ])

diff --git a/m4/ax_tls.m4 b/m4/ax_tls.m4
deleted file mode 100644 (file)
index 7c86daf..0000000
--- a/m4/ax_tls.m4
+++ /dev/null
@@ -1,87 +0,0 @@
-# ===========================================================================
-#          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 11
-
-#   Define m4_ifblank and m4_ifnblank macros from introduced in
-#   autotools 2.64 m4sugar.m4 if using an earlier autotools.
-
-ifdef([m4_ifblank], [], [
-m4_define([m4_ifblank],
-[m4_if(m4_translit([[$1]],  [ ][       ][
-]), [], [$2], [$3])])
-])
-
-
-ifdef([m4_ifnblank], [], [
-m4_define([m4_ifnblank],
-[m4_if(m4_translit([[$1]],  [ ][       ][
-]), [], [$3], [$2])])
-])
-
-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_LINK(
-               [$ax_tls_keyword int foo;],
-               [++foo;],
-               [ac_cv_tls=$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/urcu/tls-compat.h b/urcu/tls-compat.h
index 8ac1ea0615ddc2eb91ee51e9e15b89bd094d4c81..325b01b234c4b5f590742e830a1c3715ad9661e3 100644 (file)
--- a/urcu/tls-compat.h
+++ b/urcu/tls-compat.h
@@ -32,7 +32,17 @@
 extern "C" {
 #endif
 
-#ifdef CONFIG_RCU_TLS  /* Based on ax_tls.m4 */
+#ifdef CONFIG_RCU_TLS
+
+#if defined (__cplusplus) && (__cplusplus >= 201103L)
+# define URCU_TLS_STORAGE_CLASS        thread_local
+#elif defined (__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)
+# define URCU_TLS_STORAGE_CLASS        _Thread_local
+#elif defined (_MSC_VER)
+# define URCU_TLS_STORAGE_CLASS        __declspec(thread)
+#else
+# define URCU_TLS_STORAGE_CLASS        __thread
+#endif
 
 /*
  * Hint: How to define/declare TLS variables of compound types
@@ -65,10 +75,10 @@ extern "C" {
  */
 
 # define DECLARE_URCU_TLS(type, name)  \
-       CONFIG_RCU_TLS type name
+       URCU_TLS_STORAGE_CLASS type name
 
 # define DEFINE_URCU_TLS(type, name)   \
-       CONFIG_RCU_TLS type name
+       URCU_TLS_STORAGE_CLASS type name
 
 # define URCU_TLS(name)                (name)