Run server constructor in a threadpool as it's synchronous

daphne/http_protocol.py

@@ -3,6 +3,7 @@ import time
 import traceback
 from urllib.parse import unquote
 
+from twisted.internet.defer import inlineCallbacks
 from twisted.internet.interfaces import IProtocolNegotiationFactory
 from twisted.protocols.policies import ProtocolWrapper
 from twisted.web import http
@@ -55,6 +56,7 @@ class WebRequest(http.Request):
 
     ### Twisted progress callbacks
 
+    @inlineCallbacks
     def process(self):
         try:
             self.request_start = time.time()
@@ -144,7 +146,7 @@ class WebRequest(http.Request):
                 logger.debug("HTTP %s request for %s", self.method, self.client_addr)
                 self.content.seek(0, 0)
                 # Work out the application scope and create application
-                self.application_queue = self.server.create_application(self, {
+                self.application_queue = yield self.server.create_application(self, {
                     "type": "http",
                     # TODO: Correctly say if it's 1.1 or 1.0
                     "http_version": self.clientproto.split(b"/")[-1].decode("ascii"),

daphne/server.py

@@ -24,6 +24,7 @@ from concurrent.futures import CancelledError
 
 from twisted.internet import defer, reactor
 from twisted.internet.endpoints import serverFromString
+from twisted.internet.threads import deferToThread
 from twisted.logger import STDLibLogObserver, globalLogBeginner
 from twisted.web import http
 
@@ -170,6 +171,7 @@ class Server(object):
 
     ### Internal event/message handling
 
+    @defer.inlineCallbacks
     def create_application(self, protocol, scope):
         """
         Creates a new application instance that fronts a Protocol instance
@@ -181,7 +183,7 @@ class Server(object):
         assert "application_instance" not in self.connections[protocol]
         # Make an instance of the application
         input_queue = asyncio.Queue()
-        application_instance = self.application(scope=scope)
+        application_instance = yield deferToThread(self.application, scope=scope)
         # Run it, and stash the future for later checking
         self.connections[protocol]["application_instance"] = asyncio.ensure_future(application_instance(
             receive=input_queue.get,

daphne/ws_protocol.py

@@ -66,7 +66,7 @@ class WebSocketProtocol(WebSocketServerProtocol):
                     ]
             # Make new application instance with scope
             self.path = request.path.encode("ascii")
-            self.application_queue = self.server.create_application(self, {
+            self.application_deferred = self.server.create_application(self, {
                 "type": "websocket",
                 "path": unquote(self.path.decode("ascii")),
                 "headers": self.clean_headers,
@@ -75,12 +75,25 @@ class WebSocketProtocol(WebSocketServerProtocol):
                 "server": self.server_addr,
                 "subprotocols": subprotocols,
             })
+            self.application_deferred.addCallback(self.applicationCreateWorked)
+            self.application_deferred.addErrback(self.applicationCreateFailed)
         except Exception as e:
             # Exceptions here are not displayed right, just 500.
             # Turn them into an ERROR log.
             logger.error(traceback.format_exc())
             raise
 
+        # Make a deferred and return it - we'll either call it or err it later on
+        self.handshake_deferred = defer.Deferred()
+        return self.handshake_deferred
+
+    def applicationCreateWorked(self, application_queue):
+        """
+        Called when the background thread has successfully made the application
+        instance.
+        """
+        # Store the application's queue
+        self.application_queue = application_queue
         # Send over the connect message
         self.application_queue.put_nowait({"type": "websocket.connect"})
         self.server.log_action("websocket", "connecting", {
@@ -88,9 +101,12 @@ class WebSocketProtocol(WebSocketServerProtocol):
             "client": "%s:%s" % tuple(self.client_addr) if self.client_addr else None,
         })
 
-        # Make a deferred and return it - we'll either call it or err it later on
-        self.handshake_deferred = defer.Deferred()
-        return self.handshake_deferred
+    def applicationCreateFailed(self, failure):
+        """
+        Called when application creation fails.
+        """
+        logger.error(failure)
+        return failure
 
     ### Twisted event handling