Replace deprecated flask shutdown with thread kill.

CHANGELOG.md

@@ -2,6 +2,12 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## [Unreleased]
+
+### Fixed
+
+- [#1963](https://github.com/plotly/dash/pull/1963) Fix [#1780](https://github.com/plotly/dash/issues/1780) flask shutdown deprecation warning when running dashduo threaded tests.
+
 ## [2.3.0] - 2022-03-13
 
 ### Added

dash/testing/application_runners.py

@@ -7,9 +7,9 @@
 import subprocess
 import logging
 import inspect
+import ctypes
 
 import runpy
-import flask
 import requests
 
 from dash.testing.errors import NoAppFoundError, TestingTimeoutError, ServerCloseError
@@ -102,6 +102,26 @@ def tmp_app_path(self):
         return self._tmp_app_path
 
 
+class StoppableThread(threading.Thread):
+    def get_id(self):  # pylint: disable=R1710
+        if hasattr(self, "_thread_id"):
+            return self._thread_id
+        for thread_id, thread in threading._active.items():  # pylint: disable=W0212
+            if thread is self:
+                return thread_id
+
+    def kill(self):
+        thread_id = self.get_id()
+        res = ctypes.pythonapi.PyThreadState_SetAsyncExc(
+            ctypes.c_long(thread_id), ctypes.py_object(SystemExit)
+        )
+        if res == 0:
+            raise ValueError(f"Invalid thread id: {thread_id}")
+        if res > 1:
+            ctypes.pythonapi.PyThreadState_SetAsyncExc(ctypes.c_long(thread_id), None)
+            raise SystemExit("Stopping thread failure")
+
+
 class ThreadedRunner(BaseDashRunner):
     """Runs a dash application in a thread.
 
@@ -110,25 +130,14 @@ class ThreadedRunner(BaseDashRunner):
 
     def __init__(self, keep_open=False, stop_timeout=3):
         super().__init__(keep_open=keep_open, stop_timeout=stop_timeout)
-        self.stop_route = "/_stop-{}".format(uuid.uuid4().hex)
         self.thread = None
 
-    @staticmethod
-    def _stop_server():
-        # https://werkzeug.palletsprojects.com/en/0.15.x/serving/#shutting-down-the-server
-        stopper = flask.request.environ.get("werkzeug.server.shutdown")
-        if stopper is None:
-            raise RuntimeError("Not running with the Werkzeug Server")
-        stopper()
-        return "Flask server is shutting down"
-
     # pylint: disable=arguments-differ
     def start(self, app, **kwargs):
         """Start the app server in threading flavor."""
-        app.server.add_url_rule(self.stop_route, self.stop_route, self._stop_server)
 
         def _handle_error():
-            self._stop_server()
+            self.stop()
 
         app.server.errorhandler(500)(_handle_error)
 
@@ -139,9 +148,13 @@ def run():
                 kwargs["port"] = self.port
             else:
                 self.port = kwargs["port"]
-            app.run_server(threaded=True, **kwargs)
 
-        self.thread = threading.Thread(target=run)
+            try:
+                app.run_server(threaded=True, **kwargs)
+            except SystemExit:
+                logger.info("Server stopped")
+
+        self.thread = StoppableThread(target=run)
         self.thread.daemon = True
         try:
             self.thread.start()
@@ -155,7 +168,8 @@ def run():
         wait.until(lambda: self.accessible(self.url), timeout=1)
 
     def stop(self):
-        requests.get("{}{}".format(self.url, self.stop_route))
+        self.thread.kill()
+        self.thread.join()
         wait.until_not(self.thread.is_alive, self.stop_timeout)