Add a cache for the last seen event loop to avoid lookup cost

Summary: As in title, skip lookup in `WeakKeyDictionary` for repeated `get_fiber_manager` calls on the same event loop

Reviewed By: pranavtbhat

Differential Revision: D32566214

fbshipit-source-id: 7a9305ef88538ae4ef422283bc1b8a4140b8ea33

folly/python/fiber_manager.pyx

@@ -14,6 +14,8 @@
 
 import asyncio
 from cython.operator cimport dereference as deref
+from cpython.weakref cimport PyWeakref_NewRef, PyWeakref_GetObject
+from cpython cimport PyObject
 from libcpp.memory cimport unique_ptr
 from folly.executor cimport get_executor
 from libcpp.cast cimport (
@@ -27,9 +29,20 @@ from folly.fiber_manager cimport (
     cFiberManagerOptions)
 from weakref import WeakKeyDictionary
 
+
 #asynico Loops to FiberManager
-loop_to_controller = WeakKeyDictionary()
+cdef object loop_to_controller = WeakKeyDictionary()
+
+# weak reference to the last seen event loop
+cdef object last_loop = None
+# FiberManager for the last seen event loop
+cdef object last_manager = None
 
+# cleanup callback that would clean last_manager
+# if object referenced by last_loop is collected
+def clean_last_manager(_wr):
+    global last_manager
+    last_manager = None
 
 cdef class FiberManager:
     cdef unique_ptr[cFiberManager] cManager
@@ -56,11 +69,20 @@ cdef class FiberManager:
 
 
 cdef cFiberManager* get_fiber_manager(const cFiberManagerOptions& opts):
+    global last_loop, last_manager
+
     loop = asyncio.get_event_loop()
+    cdef FiberManager manager = None
+
+    if last_loop is not None and <PyObject*>loop is PyWeakref_GetObject(last_loop):
+        manager = last_manager
+    if manager is None:
         try:
             manager = <FiberManager>(loop_to_controller[loop])
         except KeyError:
             manager = FiberManager()
             manager.init(opts)
             loop_to_controller[loop] = manager
+        last_loop = PyWeakref_NewRef(loop, clean_last_manager)
+        last_manager = manager
     return manager.cManager.get()