Add system/detail/mutex.hpp, use it in error_category_impl.hpp

include/boost/system/detail/error_category_impl.hpp

@@ -98,33 +98,26 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
 #include <boost/system/detail/std_category_impl.hpp>
+#include <boost/system/detail/mutex.hpp>
 #include <new>
 
-#if !defined(BOOST_SYSTEM_DISABLE_THREADS)
-# include <mutex>
-#endif
-
 namespace boost
 {
 namespace system
 {
 
-#if !defined(BOOST_SYSTEM_DISABLE_THREADS)
-
 namespace detail
 {
 
 template<class = void> struct stdcat_mx_holder
 {
-    static std::mutex mx_;
+    static mutex mx_;
 };
 
-template<class T> std::mutex stdcat_mx_holder<T>::mx_;
+template<class T> mutex stdcat_mx_holder<T>::mx_;
 
 } // namespace detail
 
-#endif
-
 inline void error_category::init_stdcat() const
 {
     static_assert( sizeof( stdcat_ ) >= sizeof( boost::system::detail::std_category ), "sizeof(stdcat_) is not enough for std_category" );
@@ -137,9 +130,7 @@ inline void error_category::init_stdcat() const
 
 #endif
 
-#if !defined(BOOST_SYSTEM_DISABLE_THREADS)
-    std::lock_guard<std::mutex> lk( boost::system::detail::stdcat_mx_holder<>::mx_ );
-#endif
+    system::detail::lock_guard<system::detail::mutex> lk( system::detail::stdcat_mx_holder<>::mx_ );
 
     if( sc_init_.load( std::memory_order_acquire ) == 0 )
     {

include/boost/system/detail/mutex.hpp

@@ -0,0 +1,88 @@
+#ifndef BOOST_SYSTEM_DETAIL_MUTEX_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_MUTEX_HPP_INCLUDED
+
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/config.hpp>
+
+#if defined(BOOST_SYSTEM_DISABLE_THREADS)
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+struct mutex
+{
+    void lock()
+    {
+    }
+
+    void unlock()
+    {
+    }
+};
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#else
+
+#include <mutex>
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+using std::mutex;
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+template<class Mtx> class lock_guard
+{
+private:
+
+    Mtx& mtx_;
+
+private:
+
+    lock_guard( lock_guard const& );
+    lock_guard& operator=( lock_guard const& );
+
+public:
+
+    explicit lock_guard( Mtx& mtx ): mtx_( mtx )
+    {
+        mtx_.lock();
+    }
+
+    ~lock_guard()
+    {
+        mtx_.unlock();
+    }
+};
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_MUTEX_HPP_INCLUDED