Sockets are normally ready for writing without blocking if a write to the network buffer for that socket can execute, regardless of whether that data can be sent immediately.

• 如果某个套接字到网络缓冲区的写操作能够执行,那么该套接字通常就是无阻塞地为写操作做好准备的,而不管数据是否能够立即发送。