Change default HTTP Server to WSGI Server

Signed-off-by: Emil Madsen <sovende@gmail.com>

prometheus_client/exposition.py

@@ -6,7 +6,7 @@
 import socket
 import sys
 import threading
-from wsgiref.simple_server import make_server, WSGIRequestHandler
+from wsgiref.simple_server import make_server, WSGIServer, WSGIRequestHandler
 
 from .openmetrics import exposition as openmetrics
 from .registry import REGISTRY
@@ -64,15 +64,26 @@ def log_message(self, format, *args):
         """Log nothing."""
 
 
+class ThreadingWSGIServer(ThreadingMixIn, WSGIServer):
+    """Thread per request HTTP server."""
+    # Make worker threads "fire and forget". Beginning with Python 3.7 this
+    # prevents a memory leak because ``ThreadingMixIn`` starts to gather all
+    # non-daemon threads in a list in order to join on them at server close.
+    daemon_threads = True
+
+
 def start_wsgi_server(port, addr='', registry=REGISTRY):
     """Starts a WSGI server for prometheus metrics as a daemon thread."""
     app = make_wsgi_app(registry)
-    httpd = make_server(addr, port, app, handler_class=_SilentHandler)
+    httpd = make_server(addr, port, app, ThreadingWSGIServer, handler_class=_SilentHandler)
     t = threading.Thread(target=httpd.serve_forever)
     t.daemon = True
     t.start()
 
 
+start_http_server = start_wsgi_server
+
+
 def generate_latest(registry=REGISTRY):
     """Returns the metrics from the registry in latest text format as a string."""
 
@@ -181,25 +192,6 @@ def factory(cls, registry):
         return MyMetricsHandler
 
 
-class _ThreadingSimpleServer(ThreadingMixIn, HTTPServer):
-    """Thread per request HTTP server."""
-    # Make worker threads "fire and forget". Beginning with Python 3.7 this
-    # prevents a memory leak because ``ThreadingMixIn`` starts to gather all
-    # non-daemon threads in a list in order to join on them at server close.
-    # Enabling daemon threads virtually makes ``_ThreadingSimpleServer`` the
-    # same as Python 3.7's ``ThreadingHTTPServer``.
-    daemon_threads = True
-
-
-def start_http_server(port, addr='', registry=REGISTRY):
-    """Starts an HTTP server for prometheus metrics as a daemon thread"""
-    CustomMetricsHandler = MetricsHandler.factory(registry)
-    httpd = _ThreadingSimpleServer((addr, port), CustomMetricsHandler)
-    t = threading.Thread(target=httpd.serve_forever)
-    t.daemon = True
-    t.start()
-
-
 def write_to_textfile(path, registry):
     """Write metrics to the given path.