gh-106751: selectors: optimize EpollSelector.select()

Lib/selectors.py

@@ -430,6 +430,9 @@ class PollSelector(_PollLikeSelector):
 
 if hasattr(select, 'epoll'):
 
+    _NOT_EPOLLIN = ~select.EPOLLIN
+    NOT_EPOLLOUT = ~select.EPOLLOUT
+
     class EpollSelector(_PollLikeSelector):
         """Epoll-based selector."""
         _selector_cls = select.epoll
@@ -452,23 +455,28 @@ def select(self, timeout=None):
             # epoll_wait() expects `maxevents` to be greater than zero;
             # we want to make sure that `select()` can be called when no
             # FD is registered.
-            max_ev = max(len(self._fd_to_key), 1)
+            max_ev = len(self._fd_to_key) or 1
 
             ready = []
             try:
                 fd_event_list = self._selector.poll(timeout, max_ev)
             except InterruptedError:
                 return ready
-            for fd, event in fd_event_list:
-                events = 0
-                if event & ~select.EPOLLIN:
-                    events |= EVENT_WRITE
-                if event & ~select.EPOLLOUT:
-                    events |= EVENT_READ
 
-                key = self._fd_to_key.get(fd)
+            fd_to_key = self._fd_to_key
+            for fd, event in fd_event_list:
+                key = fd_to_key.get(fd)
                 if key:
-                    ready.append((key, events & key.events))
+                    ready.append(
+                        (
+                            key,
+                            (
+                                (event & NOT_EPOLLIN and EVENT_WRITE)
+                                | (event & NOT_EPOLLOUT and EVENT_READ)
+                            )
+                            & key.events
+                        )
+                    )
             return ready
 
         def close(self):

Misc/NEWS.d/next/Library/2023-07-14-20-31-09.gh-issue-106751.52F6yQ.rst

@@ -0,0 +1 @@
+:mod:`selectors`: Reduce EpollSelector overhead by moving code outside of the loop and avoiding a call to ``max()``.