diff --git a/include/nana/threads/pool.hpp b/include/nana/threads/pool.hpp
index 16edac1f..38d9952e 100644
--- a/include/nana/threads/pool.hpp
+++ b/include/nana/threads/pool.hpp
@@ -54,11 +54,17 @@ namespace threads
 
 		struct task_signal;
 		class impl;
+
+		pool(const pool&) = delete;
+		pool& operator=(const pool&) = delete;
 	public:
 		pool();                             ///< Creates a group of threads.
+		pool(pool&&);
 		pool(std::size_t thread_number);    ///< Creates a number of threads specifed by thread_number.
 		~pool();    ///< waits for the all running tasks till they are finished and skips all the queued tasks.
 
+		pool& operator=(pool&&);
+
 		template<typename Function>
 		void push(const Function& f)
 		{
diff --git a/source/gui/detail/bedrock_posix.cpp b/source/gui/detail/bedrock_posix.cpp
index 3282a32e..4f74f5a9 100644
--- a/source/gui/detail/bedrock_posix.cpp
+++ b/source/gui/detail/bedrock_posix.cpp
@@ -1158,7 +1158,9 @@ namespace detail
 		}
 
 		++(context->event_pump_ref_count);
-		wd_manager().internal_lock().revert();
+
+		auto & lock = wd_manager().internal_lock();
+		lock.revert();
 		
 		native_window_type owner_native = 0;
 		core_window_t * owner = 0;
@@ -1183,8 +1185,9 @@ namespace detail
 				owner->flags.enabled = true;
 			native_interface::enable_window(owner_native, true);
 		}
-		
-		wd_manager().internal_lock().forward();
+
+		lock.forward();
+
 		if(0 == --(context->event_pump_ref_count))
 		{
 			if(0 == modal_window || 0 == context->window_count)
diff --git a/source/gui/detail/window_manager.cpp b/source/gui/detail/window_manager.cpp
index 984988ee..e301ca5e 100644
--- a/source/gui/detail/window_manager.cpp
+++ b/source/gui/detail/window_manager.cpp
@@ -335,7 +335,7 @@ namespace detail
 
 			void window_manager::revertible_mutex::revert()
 			{
-				if(impl_->thread.ref && (impl_->thread.tid == nana::system::this_thread_id()))
+				if(impl_->thread.tid == nana::system::this_thread_id())
 				{
 					std::size_t cnt = impl_->thread.ref;
 
@@ -346,24 +346,30 @@ namespace detail
 					for (std::size_t i = 0; i < cnt; ++i)
 						impl_->mutex.unlock();
 				}
+				else
+					throw std::runtime_error("The revert is not allowed");
 			}
 
 			void window_manager::revertible_mutex::forward()
 			{
 				impl_->mutex.lock();
+				
 				if(impl_->invoke_stack.size())
 				{
 					auto thr = impl_->invoke_stack.back();
+
+					impl_->invoke_stack.pop_back();
+					
 					if(thr.tid == nana::system::this_thread_id())
 					{
-						impl_->invoke_stack.pop_back();
 						for (std::size_t i = 0; i < thr.ref; ++i)
 							impl_->mutex.lock();
 						impl_->thread = thr;
 					}
 					else
-						throw std::runtime_error("Nana.GUI: The forward is not matched.");
+						throw std::runtime_error("The forward is not matched. Please report this issue");
 				}
+
 				impl_->mutex.unlock();
 			}
 		//end class revertible_mutex
diff --git a/source/gui/programming_interface.cpp b/source/gui/programming_interface.cpp
index 94446c8b..486e6fae 100644
--- a/source/gui/programming_interface.cpp
+++ b/source/gui/programming_interface.cpp
@@ -992,33 +992,30 @@ namespace API
 
 	void modal_window(window wd)
 	{
+		auto const iwd = reinterpret_cast<basic_window*>(wd);
+		internal_scope_guard isg;
+
+		if (!restrict::wd_manager().available(iwd))
+			return;
+
+		if ((iwd->other.category == category::flags::root) && (iwd->flags.modal == false))
 		{
-			auto const iwd = reinterpret_cast<basic_window*>(wd);
-			internal_scope_guard isg;
-
-			if (!restrict::wd_manager().available(iwd))
-				return;
-
-			if ((iwd->other.category == category::flags::root) && (iwd->flags.modal == false))
-			{
-				iwd->flags.modal = true;
+			iwd->flags.modal = true;
 #if defined(NANA_X11)
-				interface_type::set_modal(iwd->root);
+			interface_type::set_modal(iwd->root);
 #endif
-				restrict::wd_manager().show(iwd, true);
-			}
-			else
-				return;
+			restrict::wd_manager().show(iwd, true);
 		}
+		else
+			return;
 
-		//modal has to guarantee that does not lock the mutex of window_manager before invokeing the pump_event,
-		//otherwise, the modal will prevent the other thread access the window.
 		restrict::bedrock.pump_event(wd, true);
 	}
 
 	void wait_for(window wd)
 	{
-		if (wd)
+		internal_scope_guard lock;
+		if (restrict::wd_manager().available(reinterpret_cast<basic_window*>(wd)))
 			restrict::bedrock.pump_event(wd, false);
 	}
 
diff --git a/source/gui/wvl.cpp b/source/gui/wvl.cpp
index 33f027f3..27e7e5ea 100644
--- a/source/gui/wvl.cpp
+++ b/source/gui/wvl.cpp
@@ -46,6 +46,7 @@ namespace nana
 
 	void pump()
 	{
+		internal_scope_guard lock;
 		detail::bedrock::instance().pump_event(nullptr, false);
 	}
 
diff --git a/source/threads/pool.cpp b/source/threads/pool.cpp
index f1237887..0e2c6c29 100644
--- a/source/threads/pool.cpp
+++ b/source/threads/pool.cpp
@@ -356,11 +356,28 @@ namespace threads
 		{
 		}
 
+		pool::pool(pool&& other)
+			: pool()
+		{
+			std::swap(impl_, other.impl_);
+		}
+
 		pool::pool(std::size_t thread_number)
 			: impl_(new impl(thread_number))
 		{
 		}
 
+		pool& pool::operator=(pool&& other)
+		{
+			if(this != &other)
+			{
+				delete impl_;
+				impl_ = other.impl_;
+				other.impl_ = new impl(4);
+			}
+			return *this;
+		}
+
 		pool::~pool()
 		{
 			delete impl_;