mutex.hpp: Optimise some atomics memory ordering

rt/include/typon/mutex.hpp

@@ -25,6 +25,8 @@ namespace typon
       std::atomic<std::uintptr_t> _stack { 0 };
     };
 
+    using enum std::memory_order;
+
     std::atomic<Node *> _state { nullptr };
     Node * _waiters { nullptr };
 
@@ -36,12 +38,13 @@ namespace typon
 
         bool await_ready() noexcept
         {
+          std::atomic<Node *> & state = _mutex->_state;
           Node * next = nullptr;
           for(;;)
           {
             // _next must be properly set before updating _state
             _next = next;
-            if(_mutex->_state.compare_exchange_weak(next, this))
+            if(state.compare_exchange_weak(next, this, acq_rel, relaxed))
             {
               return !next;
             }
@@ -64,12 +67,11 @@ namespace typon
           Node * waiter = _mutex->_waiters;
           if (!waiter)
           {
-            Node * state = this;
-            if (_mutex->_state.compare_exchange_strong(state, nullptr))
+            Node * next = this;
+            if (_mutex->_state.compare_exchange_strong(next, nullptr, acq_rel))
             {
               return;
             }
-            auto next = state;
             while (next != this)
             {
               auto tmp = next->_next;