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Gets the non-blocking mode of the socket.
bool non_blocking() const;
            true if the socket's synchronous operations will fail with
            asio::error::would_block if they are unable to perform the
            requested operation immediately. If false, synchronous operations
            will block until complete.
          
            The non-blocking mode has no effect on the behaviour of asynchronous
            operations. Asynchronous operations will never fail with the error asio::error::would_block.