Some amount of confusion arises, however, from the fact that the closesocket function implicitly causes a shutdown sequence to occur if it has not already happened.
とりあえずclosesocketすればshutdownも自動でされる、という使い方をしているのがよくあるとのこと。
In fact, it has become a rather common programming practice to rely on this feature and to use closesocket to both initiate the shutdown sequence and deallocate the socket handle.