def _find_read_pos(self): # 尝试在_read_buffer中寻找分隔符。找到则返回分隔符末尾所处的位置，如果不能，则返回None。if self._read_delimiter is not None:if self._read_buffer:    # 查看_read_buffer中是否有之前未处理的数据while True:loc = self._read_buffer[0].find(self._read_delimiter) # 查找分隔符所出现的首部位置if loc != -1:     # 在_read_buffer的首项中找到了delimiter_len = len(self._read_delimiter)self._check_max_bytes(self._read_delimiter, loc + delimiter_len)return loc + delimiter_len    # 分隔符末尾的位置if len(self._read_buffer) == 1:break_double_prefix(self._read_buffer)self._check_max_bytes(self._read_delimiter, len(self._read_buffer[0]))return None

def _read_from_buffer(self, pos): # 将所需的数据从_read_buffer中移除，并将其作为callback的参数，然后将callback封装后添加至IOLoop._callbacks中 self._read_bytes = self._read_delimiter = self._read_regex = Noneself._read_partial = Falseself._run_read_callback(pos, False)

来看_run_read_callback源码简化版：def _run_read_callback(self, size, streaming):if streaming:callback = self._streaming_callbackelse:callback = self._read_callbackself._read_callback = self._streaming_callback = Noneif self._read_future is not None:        # 这里将_read_future进行set_resultassert callback is Nonefuture = self._read_futureself._read_future = Nonefuture.set_result(self._consume(size))if callback is not None:assert (self._read_future is None) or streamingself._run_callback(callback, self._consume(size))    # 将后者作为前者的参数，然后将前者进行封装后添加至IOLoop._callbacks中

来看_consume的源码：def _consume(self, loc): # 将self._read_buffer 的首项改为 原首项[loc:] ，然后返回 原首项[:loc]if loc == 0:return b""_merge_prefix(self._read_buffer, loc)  # 将双端队列（deque）的首项调整为指定大小。self._read_buffer_size -= locreturn self._read_buffer.popleft()来看_run_callback源码简化版：def _run_callback(self, callback, *args):# 将callback封装后添加至ioloop._callbacks中def wrapper():self._pending_callbacks -= 1try:return callback(*args)finally:self._maybe_add_error_listener()with stack_context.NullContext():self._pending_callbacks += 1self.io_loop.add_callback(wrapper)    # 将callback添加至IOLoop._callbacks中

def _merge_prefix(deque, size):"""Replace the first entries in a deque of strings with a singlestring of up to size bytes.>>> d = collections.deque(['abc', 'de', 'fghi', 'j'])>>> _merge_prefix(d, 5); print(d)deque(['abcde', 'fghi', 'j'])Strings will be split as necessary to reach the desired size.>>> _merge_prefix(d, 7); print(d)deque(['abcdefg', 'hi', 'j'])>>> _merge_prefix(d, 3); print(d)deque(['abc', 'defg', 'hi', 'j'])>>> _merge_prefix(d, 100); print(d)deque(['abcdefghij'])"""if len(deque) == 1 and len(deque[0]) <= size:returnprefix = []remaining = sizewhile deque and remaining > 0:chunk = deque.popleft()if len(chunk) > remaining:deque.appendleft(chunk[remaining:])chunk = chunk[:remaining]prefix.append(chunk)remaining -= len(chunk)if prefix:deque.appendleft(type(prefix[0])().join(prefix))if not deque:deque.appendleft(b"")

来看_read_to_buffer_loop简化版：系统缓冲中的data可能十分长，为了查找指定的字符，我们应该先读一个chunk，检查其中是否有指定的字符，若有则返回分隔符末尾所处的位置若没有则继续读第二个chunk，然后将这两个chunk合并(多字节分隔符（例如“\ r \ n”）可能跨读取缓冲区中的两个块)，重复查找过程def _read_to_buffer_loop(self):try:next_find_pos = 0self._pending_callbacks += 1while not self.closed():if self._read_to_buffer() == 0:    # 从系统缓冲中读一个chunk并将其添加至_read_buffer中，然后返回chunk的大小，如果无数据则返回0breakself._run_streaming_callback()    if self._read_buffer_size >= next_find_pos:    # _read_buffer_size 表示_read_buffer的大小pos = self._find_read_pos()    # 尝试在_read_buffer中寻找分隔符。找到则返回分隔符末尾所处的位置，如果不能，则返回None。 if pos is not None:return posnext_find_pos = self._read_buffer_size * 2return self._find_read_pos()finally:self._pending_callbacks -= 1

def _add_io_state(self, state):if self.closed():    # 连接已经关闭returnif self._state is None:self._state = ioloop.IOLoop.ERROR | state    with stack_context.NullContext():self.io_loop.add_handler(self.fileno(), self._handle_events, self._state) # 为对应socket的文件描述符添加事件及其处理函数,elif not self._state & state:self._state = self._state | stateself.io_loop.update_handler(self.fileno(), self._state)# self._handle_events 是根据events选择对应的处理函数，在这里我们假设处理函数是_handle_readdef _handle_read(self):try:pos = self._read_to_buffer_loop()except UnsatisfiableReadError:raiseexcept Exception as e:gen_log.warning("error on read: %s" % e)self.close(exc_info=True)returnif pos is not None:self._read_from_buffer(pos)returnelse:self._maybe_run_close_callback()