user_a = {“id”:1,”name”:”A”}

user_b = {“id”:2,”name”:”B”}

chat_a = { “id”:1, “user”:1, “who”:2, “name”:”B”, “new”:0, msg:[]}

chat_b = { “id”:2, “user”:2, “who”:1, “name”:”A”, “new”:0, msg:[]}

chats = dict()
...
def on_open(self):
  ...
  #通过双方id来生成一个独一无二的字符串
  min = user_a['id']
  max = user_b['id']
  if min >max:
    max = user_a['id']
    min = user_b['id']
  key = str(user_a['id'])+"_"+str(user_b['id'])
  #判断当前会话是否存在，存在则添加当前用户
  if key in chats:
    SocketHandler.chats[key].append(self)
  #不存在则创建会话，并将当前用户添加进去
  else
    SocketHandler.chats[key] = [self]

def send_to_all(key,message):
  for user in SocketHandler.chats[key]:
    user.write_message(json.dumps(message))

def on_close(self):
  ...
  #用on_open函数中的方法构造key
  if key in SocketHandler.chats:
    SocketHandler.chats[key].remove(self)#删除当前连接
    if len(SocketHandler.chats[key]) == 0:
      del SocketHandler.chats[key]#当会话无连接者则删除会话