Use the __thread keyword extension when compiling with gcc on linux x86.

asio/include/Makefile.am

@@ -109,6 +109,7 @@ nobase_include_HEADERS = \
 	asio/detail/impl/win_thread.ipp \
 	asio/detail/impl/win_tss_ptr.ipp \
 	asio/detail/io_control.hpp \
+	asio/detail/keyword_tss_ptr.hpp \
 	asio/detail/kqueue_reactor_fwd.hpp \
 	asio/detail/kqueue_reactor.hpp \
 	asio/detail/local_free_on_block_exit.hpp \

asio/include/asio/detail/config.hpp

@@ -371,4 +371,15 @@
 # endif // !defined(UNDER_CE)
 #endif // !defined(ASIO_DISABLE_SIGNAL)
 
+// Support for the __thread keyword extension.
+#if !defined(ASIO_DISABLE_THREAD_KEYWORD_EXTENSION)
+# if defined(__linux__)
+#  if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+#   if ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)) || (__GNUC__ > 3)
+#    define ASIO_HAS_THREAD_KEYWORD_EXTENSION 1
+#   endif // ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)) || (__GNUC__ > 3)
+#  endif // defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+# endif // defined(__linux__)
+#endif // !defined(ASIO_DISABLE_THREAD_KEYWORD_EXTENSION)
+
 #endif // ASIO_DETAIL_CONFIG_HPP

asio/include/asio/detail/keyword_tss_ptr.hpp

@@ -0,0 +1,70 @@
+//
+// detail/keyword_tss_ptr.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2012 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_DETAIL_KEYWORD_TSS_PTR_HPP
+#define ASIO_DETAIL_KEYWORD_TSS_PTR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_THREAD_KEYWORD_EXTENSION)
+
+#include "asio/detail/noncopyable.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename T>
+class keyword_tss_ptr
+  : private noncopyable
+{
+public:
+  // Constructor.
+  keyword_tss_ptr()
+  {
+  }
+
+  // Destructor.
+  ~keyword_tss_ptr()
+  {
+  }
+
+  // Get the value.
+  operator T*() const
+  {
+    return value_;
+  }
+
+  // Set the value.
+  void operator=(T* value)
+  {
+    value_ = value;
+  }
+
+private:
+  static __thread T* value_;
+};
+
+template <typename T>
+__thread T* keyword_tss_ptr<T>::value_;
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // defined(ASIO_HAS_THREAD_KEYWORD_EXTENSION)
+
+#endif // ASIO_DETAIL_KEYWORD_TSS_PTR_HPP

asio/include/asio/detail/tss_ptr.hpp

@@ -19,6 +19,8 @@
 
 #if !defined(BOOST_HAS_THREADS) || defined(ASIO_DISABLE_THREADS)
 # include "asio/detail/null_tss_ptr.hpp"
+#elif defined(ASIO_HAS_THREAD_KEYWORD_EXTENSION)
+# include "asio/detail/keyword_tss_ptr.hpp"
 #elif defined(BOOST_WINDOWS)
 # include "asio/detail/win_tss_ptr.hpp"
 #elif defined(BOOST_HAS_PTHREADS)
@@ -36,6 +38,8 @@ template <typename T>
 class tss_ptr
 #if !defined(BOOST_HAS_THREADS) || defined(ASIO_DISABLE_THREADS)
   : public null_tss_ptr<T>
+#elif defined(ASIO_HAS_THREAD_KEYWORD_EXTENSION)
+  : public keyword_tss_ptr<T>
 #elif defined(BOOST_WINDOWS)
   : public win_tss_ptr<T>
 #elif defined(BOOST_HAS_PTHREADS)
@@ -47,6 +51,8 @@ public:
   {
 #if !defined(BOOST_HAS_THREADS) || defined(ASIO_DISABLE_THREADS)
     null_tss_ptr<T>::operator=(value);
+#elif defined(ASIO_HAS_THREAD_KEYWORD_EXTENSION)
+    keyword_tss_ptr<T>::operator=(value);
 #elif defined(BOOST_WINDOWS)
     win_tss_ptr<T>::operator=(value);
 #elif defined(BOOST_HAS_PTHREADS)