Fix bug when max_clients kwarg is passed to AsyncHTTPClient.configure.

Closes tornadoweb#493.

tornado/httpclient.py

@@ -124,14 +124,16 @@ def handle_request(response):
     _impl_class = None
     _impl_kwargs = None
 
+    _DEFAULT_MAX_CLIENTS = 10
+
     @classmethod
     def _async_clients(cls):
         assert cls is not AsyncHTTPClient, "should only be called on subclasses"
         if not hasattr(cls, '_async_client_dict'):
             cls._async_client_dict = weakref.WeakKeyDictionary()
         return cls._async_client_dict
 
-    def __new__(cls, io_loop=None, max_clients=10, force_instance=False,
+    def __new__(cls, io_loop=None, max_clients=None, force_instance=False,
                 **kwargs):
         io_loop = io_loop or IOLoop.instance()
         if cls is AsyncHTTPClient:
@@ -149,7 +151,13 @@ def __new__(cls, io_loop=None, max_clients=10, force_instance=False,
             if cls._impl_kwargs:
                 args.update(cls._impl_kwargs)
             args.update(kwargs)
-            instance.initialize(io_loop, max_clients, **args)
+            if max_clients is not None:
+                # max_clients is special because it may be passed
+                # positionally instead of by keyword
+                args["max_clients"] = max_clients
+            elif "max_clients" not in args:
+                args["max_clients"] = AsyncHTTPClient._DEFAULT_MAX_CLIENTS
+            instance.initialize(io_loop, **args)
             if not force_instance:
                 impl._async_clients()[io_loop] = instance
             return instance
@@ -204,6 +212,15 @@ def configure(impl, **kwargs):
         AsyncHTTPClient._impl_class = impl
         AsyncHTTPClient._impl_kwargs = kwargs
 
+    @staticmethod
+    def _save_configuration():
+        return (AsyncHTTPClient._impl_class, AsyncHTTPClient._impl_kwargs)
+
+    @staticmethod
+    def _restore_configuration(saved):
+        AsyncHTTPClient._impl_class = saved[0]
+        AsyncHTTPClient._impl_kwargs = saved[1]
+
 
 class HTTPRequest(object):
     """HTTP client request object."""

tornado/test/simple_httpclient_test.py

@@ -1,16 +1,18 @@
 from __future__ import absolute_import, division, with_statement
 
 import collections
+from contextlib import closing
 import gzip
 import logging
 import re
 import socket
 
+from tornado.httpclient import AsyncHTTPClient
 from tornado.httputil import HTTPHeaders
 from tornado.ioloop import IOLoop
 from tornado.simple_httpclient import SimpleAsyncHTTPClient, _DEFAULT_CA_CERTS
 from tornado.test.httpclient_test import HTTPClientCommonTestCase, ChunkHandler, CountdownHandler, HelloWorldHandler
-from tornado.testing import AsyncHTTPTestCase, LogTrapTestCase
+from tornado.testing import AsyncHTTPTestCase, AsyncTestCase, LogTrapTestCase
 from tornado.util import b
 from tornado.web import RequestHandler, Application, asynchronous, url
 
@@ -263,3 +265,40 @@ def test_host_header(self):
         self.http_client.fetch(url, self.stop)
         response = self.wait()
         self.assertTrue(host_re.match(response.body), response.body)
+
+
+class CreateAsyncHTTPClientTestCase(AsyncTestCase, LogTrapTestCase):
+    def setUp(self):
+        super(CreateAsyncHTTPClientTestCase, self).setUp()
+        self.saved = AsyncHTTPClient._save_configuration()
+
+    def tearDown(self):
+        AsyncHTTPClient._restore_configuration(self.saved)
+        super(CreateAsyncHTTPClientTestCase, self).tearDown()
+
+    def test_max_clients(self):
+        # The max_clients argument is tricky because it was originally
+        # allowed to be passed positionally; newer arguments are keyword-only.
+        AsyncHTTPClient.configure(SimpleAsyncHTTPClient)
+        with closing(AsyncHTTPClient(
+                self.io_loop, force_instance=True)) as client:
+            self.assertEqual(client.max_clients, 10)
+        with closing(AsyncHTTPClient(
+                self.io_loop, 11, force_instance=True)) as client:
+            self.assertEqual(client.max_clients, 11)
+        with closing(AsyncHTTPClient(
+                self.io_loop, max_clients=11, force_instance=True)) as client:
+            self.assertEqual(client.max_clients, 11)
+
+        # Now configure max_clients statically and try overriding it
+        # with each way max_clients can be passed
+        AsyncHTTPClient.configure(SimpleAsyncHTTPClient, max_clients=12)
+        with closing(AsyncHTTPClient(
+                self.io_loop, force_instance=True)) as client:
+            self.assertEqual(client.max_clients, 12)
+        with closing(AsyncHTTPClient(
+                self.io_loop, max_clients=13, force_instance=True)) as client:
+            self.assertEqual(client.max_clients, 13)
+        with closing(AsyncHTTPClient(
+                self.io_loop, max_clients=14, force_instance=True)) as client:
+            self.assertEqual(client.max_clients, 14)