Revert "Added a multi-worker approach to the Tornado WSGI container."

This reverts commit 71401a4936.

Temporarily reverted this commit because the `reuse_address` on the
application's `listen` method has only been implemented in Tornado 6.2 -
and Debian stable still shipts Tornado 6.1.

platypush/backend/http/__init__.py

@@ -1,12 +1,10 @@
-import multiprocessing
 import os
 import pathlib
 import secrets
 import threading
-import time
 
 from multiprocessing import Process
-from typing import List, Mapping, Optional
+from typing import Mapping, Optional
 
 from tornado.wsgi import WSGIContainer
 from tornado.web import Application, FallbackHandler
@@ -188,7 +186,6 @@ class HttpBackend(Backend):
     """
 
     _DEFAULT_HTTP_PORT = 8008
-    """The default listen port for the webserver."""
 
     def __init__(
         self,
@@ -196,7 +193,6 @@ class HttpBackend(Backend):
         bind_address: str = '0.0.0.0',
         resource_dirs: Optional[Mapping[str, str]] = None,
         secret_key_file: Optional[str] = None,
-        num_workers: Optional[int] = None,
         **kwargs,
     ):
         """
@@ -208,13 +204,12 @@ class HttpBackend(Backend):
             the value is the absolute path to expose.
         :param secret_key_file: Path to the file containing the secret key that will be used by Flask
             (default: ``~/.local/share/platypush/flask.secret.key``).
-        :param num_workers: Number of worker processes to use (default: ``(cpu_count * 2) + 1``).
         """
 
         super().__init__(**kwargs)
 
         self.port = port
-        self._workers: List[Process] = []
+        self.server_proc = None
         self._service_registry_thread = None
         self.bind_address = bind_address
         self._io_loop: Optional[IOLoop] = None
@@ -232,7 +227,6 @@ class HttpBackend(Backend):
             or os.path.join(Config.get('workdir'), 'flask.secret.key')  # type: ignore
         )
         self.local_base_url = f'http://localhost:{self.port}'
-        self.num_workers = num_workers or (multiprocessing.cpu_count() * 2) + 1
 
     def send_message(self, *_, **__):
         self.logger.warning('Use cURL or any HTTP client to query the HTTP backend')
@@ -246,27 +240,18 @@ class HttpBackend(Backend):
             self._io_loop.stop()
             self._io_loop.close()
 
-        workers = self._workers.copy()
-        for worker in workers:
-            worker.terminate()
-
-        stop_timeout = 5
-        wait_start_time = time.time()
-        wait_max_time = wait_start_time + stop_timeout
-
-        for i, worker in enumerate(workers[::-1]):
-            worker.join(timeout=max(0, wait_max_time - time.time()))
-            if worker.is_alive():
-                worker.kill()
-
-            if worker.is_alive():
+        if self.server_proc:
+            self.server_proc.terminate()
+            self.server_proc.join(timeout=10)
+            if self.server_proc.is_alive():
+                self.server_proc.kill()
+            if self.server_proc.is_alive():
                 self.logger.info(
-                    'HTTP worker %s may be still alive at termination', worker.name
+                    'HTTP server process may be still alive at termination'
                 )
             else:
-                self._workers.pop(i)
+                self.logger.info('HTTP server process terminated')
 
-        self.logger.info('HTTP workers terminated')
         if self._service_registry_thread and self._service_registry_thread.is_alive():
             self._service_registry_thread.join(timeout=5)
             self._service_registry_thread = None
@@ -297,12 +282,15 @@ class HttpBackend(Backend):
             raise e
 
     def _web_server_proc(self):
+        def proc():
+            self.logger.info('Starting local web server on port %s', self.port)
             assert isinstance(
                 self.bus, RedisBus
             ), 'The HTTP backend only works if backed by a Redis bus'
 
             application.config['redis_queue'] = self.bus.redis_queue
             application.secret_key = self._get_secret_key()
+
             container = WSGIContainer(application)
             server = Application(
                 [
@@ -311,7 +299,7 @@ class HttpBackend(Backend):
                 ]
             )
 
-        server.listen(address=self.bind_address, port=self.port, reuse_port=True)
+            server.listen(address=self.bind_address, port=self.port)
             self._io_loop = IOLoop.instance()
 
             try:
@@ -320,6 +308,8 @@ class HttpBackend(Backend):
                 if not self.should_stop():
                     raise e
 
+        return proc
+
     def _register_service(self):
         try:
             self.register_service(port=self.port)
@@ -335,22 +325,9 @@ class HttpBackend(Backend):
         self._service_registry_thread.start()
 
     def _run_web_server(self):
-        self.logger.info(
-            'Starting local web server on port %s with %d service workers',
-            self.port,
-            self.num_workers,
-        )
-
-        workers = [
-            Process(target=self._web_server_proc, name=f'WebWorker#{i + 1}')
-            for i in range(self.num_workers)
-        ]
-
-        for worker in workers:
-            worker.start()
-
-        for worker in workers:
-            worker.join()
+        self.server_proc = Process(target=self._web_server_proc(), name='WebServer')
+        self.server_proc.start()
+        self.server_proc.join()
 
     def run(self):
         super().run()