diff --git a/channel/chat_channel.py b/channel/chat_channel.py
index 27f3af0..7e2df3a 100644
--- a/channel/chat_channel.py
+++ b/channel/chat_channel.py
@@ -337,24 +337,27 @@ class ChatChannel(Channel):
         while True:
             with self.lock:
                 session_ids = list(self.sessions.keys())
-                for session_id in session_ids:
+            for session_id in session_ids:
+                with self.lock:
                     context_queue, semaphore = self.sessions[session_id]
-                    if semaphore.acquire(blocking=False):  # 等线程处理完毕才能删除
-                        if not context_queue.empty():
-                            context = context_queue.get()
-                            logger.debug("[chat_channel] consume context: {}".format(context))
-                            future: Future = handler_pool.submit(self._handle, context)
-                            future.add_done_callback(self._thread_pool_callback(session_id, context=context))
+                if semaphore.acquire(blocking=False):  # 等线程处理完毕才能删除
+                    if not context_queue.empty():
+                        context = context_queue.get()
+                        logger.debug("[chat_channel] consume context: {}".format(context))
+                        future: Future = handler_pool.submit(self._handle, context)
+                        future.add_done_callback(self._thread_pool_callback(session_id, context=context))
+                        with self.lock:
                             if session_id not in self.futures:
                                 self.futures[session_id] = []
                             self.futures[session_id].append(future)
-                        elif semaphore._initial_value == semaphore._value + 1:  # 除了当前，没有任务再申请到信号量，说明所有任务都处理完毕
+                    elif semaphore._initial_value == semaphore._value + 1:  # 除了当前，没有任务再申请到信号量，说明所有任务都处理完毕
+                        with self.lock:
                             self.futures[session_id] = [t for t in self.futures[session_id] if not t.done()]
                             assert len(self.futures[session_id]) == 0, "thread pool error"
                             del self.sessions[session_id]
-                        else:
-                            semaphore.release()
-            time.sleep(0.1)
+                    else:
+                        semaphore.release()
+            time.sleep(0.2)
 
     # 取消session_id对应的所有任务，只能取消排队的消息和已提交线程池但未执行的任务
     def cancel_session(self, session_id):