Support customizing the distribution of multipal io_contexts.

asio @ 08a7029c

-Subproject commit d038fb3c2fb56fb91ff1d17b0715cff7887aa09e
+Subproject commit 08a7029cb10c911b6fb66fb015217a431206e52c

examples/udp_test/udp_test.cpp

@@ -40,7 +40,7 @@ template <typename Socket> std::thread create_sync_recv_thread(Socket& socket)
 	});
 }
 
-//because st_asio_wrapper is header only, it cannot provide the implementation of below global function, but kcp needs it,
+//because ascs is header only, it cannot provide the implementation of below global function, but kcp needs it,
 //you're supposed to provide it and call reliable_socket_base::output directly in it, like:
 int output(const char* buf, int len, ikcpcb * kcp, void* user) {return ((single_reliable_socket_service*) user)->output(buf, len);}
 

include/ascs/service_pump.h

@@ -164,15 +164,15 @@ public:
 		throw "no available io_context!";
 	}
 
-	void return_io_context(const asio::execution_context& io_context)
+	void return_io_context(const asio::execution_context& io_context, unsigned refs = 1)
 	{
 		if (!single_io_context)
-			ascs::do_something_to_one(context_can, context_can_mutex, [&](context& item) {return &io_context != &item.io_context ? false : (--item.refs, true);});
+			ascs::do_something_to_one(context_can, context_can_mutex, [&](context& item) {return &io_context != &item.io_context ? false : (item.refs -= refs, true);});
 	}
-	void assign_io_context(const asio::execution_context& io_context)
+	void assign_io_context(const asio::execution_context& io_context, unsigned refs = 1)
 	{
 		if (!single_io_context)
-			ascs::do_something_to_one(context_can, context_can_mutex, [&](context& item) {return &io_context != &item.io_context ? false : (++item.refs, true);});
+			ascs::do_something_to_one(context_can, context_can_mutex, [&](context& item) {return &io_context != &item.io_context ? false : (item.refs += refs, true);});
 	}
 
 	object_type find(int id)