Always use '__thread' for Thread local storage except on MSVC

Use the GCC extension '__thread' [1] for Thread local storage on all C
and C++ compilers except MSVC.

While C11 and C++11 respectively offer '_Thread_local' and
'thread_local' as potentialy faster implementations, they offer no
guarantees of compatibility when used in a library interface which might
be used by both C and C++ client code.

[1] https://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html

Change-Id: If4fe8bcdbda24b21dedf382112bd5c5f836c00c8
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/urcu/tls-compat.h b/include/urcu/tls-compat.h
index 25cf375a23462dc53536c5da2cc4d5206466081b..a2c94ded9cd9833558bb25d19b9908c6f47a9007 100644 (file)
--- a/include/urcu/tls-compat.h
+++ b/include/urcu/tls-compat.h
@@ -35,15 +35,14 @@ extern "C" {
 #ifdef CONFIG_RCU_TLS
 
 /*
- * Don't use C++ 'thread_local' on MacOs, the implementation is incompatible
- * with C and will result in a link error when accessing an extern variable
- * provided by the C library from C++ code.
+ * Default to '__thread' on all C and C++ compilers except MSVC. While C11 has
+ * '_Thread_local' and C++11 has 'thread_local', only '__thread' seems to have
+ * a compatible implementation when linking public extern symbols across
+ * language boundaries.
+ *
+ * For more details, see 'https://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html'.
  */
-#if defined (__cplusplus) && (__cplusplus >= 201103L) && !defined(__APPLE__)
-# 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)
+#if defined(_MSC_VER)
 # define URCU_TLS_STORAGE_CLASS        __declspec(thread)
 #else
 # define URCU_TLS_STORAGE_CLASS        __thread