Greedy ioloop working (#1870)

Enable the SYN_GREEDY_CORO environment variable
Set the ioloop into debug mode when this is enabled
This should be considered for use in development/debugging, not for general production use.

synapse/glob.py

@@ -1,9 +1,12 @@
 import os
 import signal
 import asyncio
+import logging
 import threading
 import faulthandler
 
+logger = logging.getLogger(__name__)
+
 _glob_loop = None
 _glob_thrd = None
 
@@ -47,21 +50,26 @@ def initloop():
             _glob_loop = asyncio.get_running_loop()
             # if we get here, it's us!
             _glob_thrd = threading.currentThread()
+            # Enable debug and greedy coro collection
+            setGreedCoro(_glob_loop)
 
         except RuntimeError:
-
-            # otherwise, lets fire one...
             _glob_loop = asyncio.new_event_loop()
-            greedy_threshold = os.environ.get('SYN_GREEDY_CORO')
-            if greedy_threshold is not None:
-                _glob_loop.slow_callback_duration = float(greedy_threshold)
+            setGreedCoro(_glob_loop)
 
             _glob_thrd = threading.Thread(target=_glob_loop.run_forever, name='SynLoop')
             _glob_thrd.setDaemon(True)
             _glob_thrd.start()
 
     return _glob_loop
 
+def setGreedCoro(loop: asyncio.AbstractEventLoop):
+    greedy_threshold = os.environ.get('SYN_GREEDY_CORO')
+    if greedy_threshold is not None:  # pragma: no cover
+        logger.info(f'Setting ioloop.slow_callback_duration to {greedy_threshold}')
+        loop.set_debug(True)
+        loop.slow_callback_duration = float(greedy_threshold)
+
 def iAmLoop():
     initloop()
     return threading.currentThread() == _glob_thrd