#30014: refactor poll-related classes (#1035)

* #30014: refactor poll-related classes so that poll(), epoll() and devpoll() share the same methods for register(), unregister(), close() and select()

* remove unused attribute

* use specific class attributes instead of select.* constants

* have all classes except SelectSelector a _selector attribute

* BaseException -> Exception

* be explicit in defining a close() method only for selectors which have it

* fix AttributeError

1 files changed, 84 insertions, 132 deletions

diff --git a/Lib/selectors.py b/Lib/selectors.py
index e7bc517730..f29d11fc6a 100644
--- a/Lib/selectors.py
+++ b/Lib/selectors.py
@@ -339,92 +339,86 @@ class SelectSelector(_BaseSelectorImpl):
         return ready
 
 
-if hasattr(select, 'poll'):
+class _PollLikeSelector(_BaseSelectorImpl):
+    """Base class shared between poll, epoll and devpoll selectors."""
+    _selector_cls = None
 
-    class PollSelector(_BaseSelectorImpl):
-        """Poll-based selector."""
+    def __init__(self):
+        super().__init__()
+        self._selector = self._selector_cls()
 
-        def __init__(self):
-            super().__init__()
-            self._poll = select.poll()
+    def register(self, fileobj, events, data=None):
+        key = super().register(fileobj, events, data)
+        poller_events = 0
+        if events & EVENT_READ:
+            poller_events |= self._EVENT_READ
+        if events & EVENT_WRITE:
+            poller_events |= self._EVENT_WRITE
+        try:
+            self._selector.register(key.fd, poller_events)
+        except Exception:
+            super().unregister(fileobj)
+            raise
+        return key
 
-        def register(self, fileobj, events, data=None):
-            key = super().register(fileobj, events, data)
-            poll_events = 0
-            if events & EVENT_READ:
-                poll_events |= select.POLLIN
-            if events & EVENT_WRITE:
-                poll_events |= select.POLLOUT
-            self._poll.register(key.fd, poll_events)
-            return key
+    def unregister(self, fileobj):
+        key = super().unregister(fileobj)
+        try:
+            self._selector.unregister(key.fd)
+        except OSError:
+            # This can happen if the FD was closed since it
+            # was registered.
+            pass
+        return key
 
-        def unregister(self, fileobj):
-            key = super().unregister(fileobj)
-            self._poll.unregister(key.fd)
-            return key
+    def select(self, timeout=None):
+        # This is shared between poll() and epoll().
+        # epoll() has a different signature and handling of timeout parameter.
+        if timeout is None:
+            timeout = None
+        elif timeout <= 0:
+            timeout = 0
+        else:
+            # poll() has a resolution of 1 millisecond, round away from
+            # zero to wait *at least* timeout seconds.
+            timeout = math.ceil(timeout * 1e3)
+        ready = []
+        try:
+            fd_event_list = self._selector.poll(timeout)
+        except InterruptedError:
+            return ready
+        for fd, event in fd_event_list:
+            events = 0
+            if event & ~self._EVENT_READ:
+                events |= EVENT_WRITE
+            if event & ~self._EVENT_WRITE:
+                events |= EVENT_READ
 
-        def select(self, timeout=None):
-            if timeout is None:
-                timeout = None
-            elif timeout <= 0:
-                timeout = 0
-            else:
-                # poll() has a resolution of 1 millisecond, round away from
-                # zero to wait *at least* timeout seconds.
-                timeout = math.ceil(timeout * 1e3)
-            ready = []
-            try:
-                fd_event_list = self._poll.poll(timeout)
-            except InterruptedError:
-                return ready
-            for fd, event in fd_event_list:
-                events = 0
-                if event & ~select.POLLIN:
-                    events |= EVENT_WRITE
-                if event & ~select.POLLOUT:
-                    events |= EVENT_READ
+            key = self._key_from_fd(fd)
+            if key:
+                ready.append((key, events & key.events))
+        return ready
 
-                key = self._key_from_fd(fd)
-                if key:
-                    ready.append((key, events & key.events))
-            return ready
+
+if hasattr(select, 'poll'):
+
+    class PollSelector(_PollLikeSelector):
+        """Poll-based selector."""
+        _selector_cls = select.poll
+        _EVENT_READ = select.POLLIN
+        _EVENT_WRITE = select.POLLOUT
 
 
 if hasattr(select, 'epoll'):
 
-    class EpollSelector(_BaseSelectorImpl):
+    class EpollSelector(_PollLikeSelector):
         """Epoll-based selector."""
-
-        def __init__(self):
-            super().__init__()
-            self._epoll = select.epoll()
+        _selector_cls = select.epoll
+        _EVENT_READ = select.EPOLLIN
+        _EVENT_WRITE = select.EPOLLOUT
 
         def fileno(self):
-            return self._epoll.fileno()
-
-        def register(self, fileobj, events, data=None):
-            key = super().register(fileobj, events, data)
-            epoll_events = 0
-            if events & EVENT_READ:
-                epoll_events |= select.EPOLLIN
-            if events & EVENT_WRITE:
-                epoll_events |= select.EPOLLOUT
-            try:
-                self._epoll.register(key.fd, epoll_events)
-            except BaseException:
-                super().unregister(fileobj)
-                raise
-            return key
-
-        def unregister(self, fileobj):
-            key = super().unregister(fileobj)
-            try:
-                self._epoll.unregister(key.fd)
-            except OSError:
-                # This can happen if the FD was closed since it
-                # was registered.
-                pass
-            return key
+            return self._selector.fileno()
 
         def select(self, timeout=None):
             if timeout is None:
@@ -443,7 +437,7 @@ if hasattr(select, 'epoll'):
 
             ready = []
             try:
-                fd_event_list = self._epoll.poll(timeout, max_ev)
+                fd_event_list = self._selector.poll(timeout, max_ev)
             except InterruptedError:
                 return ready
             for fd, event in fd_event_list:
@@ -459,65 +453,23 @@ if hasattr(select, 'epoll'):
             return ready
 
         def close(self):
-            self._epoll.close()
+            self._selector.close()
             super().close()
 
 
 if hasattr(select, 'devpoll'):
 
-    class DevpollSelector(_BaseSelectorImpl):
+    class DevpollSelector(_PollLikeSelector):
         """Solaris /dev/poll selector."""
-
-        def __init__(self):
-            super().__init__()
-            self._devpoll = select.devpoll()
+        _selector_cls = select.devpoll
+        _EVENT_READ = select.POLLIN
+        _EVENT_WRITE = select.POLLOUT
 
         def fileno(self):
-            return self._devpoll.fileno()
-
-        def register(self, fileobj, events, data=None):
-            key = super().register(fileobj, events, data)
-            poll_events = 0
-            if events & EVENT_READ:
-                poll_events |= select.POLLIN
-            if events & EVENT_WRITE:
-                poll_events |= select.POLLOUT
-            self._devpoll.register(key.fd, poll_events)
-            return key
-
-        def unregister(self, fileobj):
-            key = super().unregister(fileobj)
-            self._devpoll.unregister(key.fd)
-            return key
-
-        def select(self, timeout=None):
-            if timeout is None:
-                timeout = None
-            elif timeout <= 0:
-                timeout = 0
-            else:
-                # devpoll() has a resolution of 1 millisecond, round away from
-                # zero to wait *at least* timeout seconds.
-                timeout = math.ceil(timeout * 1e3)
-            ready = []
-            try:
-                fd_event_list = self._devpoll.poll(timeout)
-            except InterruptedError:
-                return ready
-            for fd, event in fd_event_list:
-                events = 0
-                if event & ~select.POLLIN:
-                    events |= EVENT_WRITE
-                if event & ~select.POLLOUT:
-                    events |= EVENT_READ
-
-                key = self._key_from_fd(fd)
-                if key:
-                    ready.append((key, events & key.events))
-            return ready
+            return self._selector.fileno()
 
         def close(self):
-            self._devpoll.close()
+            self._selector.close()
             super().close()
 
 
@@ -528,10 +480,10 @@ if hasattr(select, 'kqueue'):
 
         def __init__(self):
             super().__init__()
-            self._kqueue = select.kqueue()
+            self._selector = select.kqueue()
 
         def fileno(self):
-            return self._kqueue.fileno()
+            return self._selector.fileno()
 
         def register(self, fileobj, events, data=None):
             key = super().register(fileobj, events, data)
@@ -539,12 +491,12 @@ if hasattr(select, 'kqueue'):
                 if events & EVENT_READ:
                     kev = select.kevent(key.fd, select.KQ_FILTER_READ,
                                         select.KQ_EV_ADD)
-                    self._kqueue.control([kev], 0, 0)
+                    self._selector.control([kev], 0, 0)
                 if events & EVENT_WRITE:
                     kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
                                         select.KQ_EV_ADD)
-                    self._kqueue.control([kev], 0, 0)
-            except BaseException:
+                    self._selector.control([kev], 0, 0)
+            except Exception:
                 super().unregister(fileobj)
                 raise
             return key
@@ -555,7 +507,7 @@ if hasattr(select, 'kqueue'):
                 kev = select.kevent(key.fd, select.KQ_FILTER_READ,
                                     select.KQ_EV_DELETE)
                 try:
-                    self._kqueue.control([kev], 0, 0)
+                    self._selector.control([kev], 0, 0)
                 except OSError:
                     # This can happen if the FD was closed since it
                     # was registered.
@@ -564,7 +516,7 @@ if hasattr(select, 'kqueue'):
                 kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
                                     select.KQ_EV_DELETE)
                 try:
-                    self._kqueue.control([kev], 0, 0)
+                    self._selector.control([kev], 0, 0)
                 except OSError:
                     # See comment above.
                     pass
@@ -575,7 +527,7 @@ if hasattr(select, 'kqueue'):
             max_ev = len(self._fd_to_key)
             ready = []
             try:
-                kev_list = self._kqueue.control(None, max_ev, timeout)
+                kev_list = self._selector.control(None, max_ev, timeout)
             except InterruptedError:
                 return ready
             for kev in kev_list:
@@ -593,7 +545,7 @@ if hasattr(select, 'kqueue'):
             return ready
 
         def close(self):
-            self._kqueue.close()
+            self._selector.close()
             super().close()