bpo-41273: asyncio's proactor read transport's better performance by using recv_into instead of recv (#21442)

* bpo-41273: Proactor transport read loop to use recv_into

By using recv_into instead of recv we do not allocate a new buffer each
time _loop_reading calls recv.

This betters performance for any stream using proactor (basically any
asyncio stream on windows).

* bpo-41273: Double proactor read transport buffer size

By doubling the read buffer size we get better performance.

Lib/asyncio/proactor_events.py

@@ -179,11 +179,12 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
     """Transport for read pipes."""
 
     def __init__(self, loop, sock, protocol, waiter=None,
-                 extra=None, server=None):
-        self._pending_data = None
+                 extra=None, server=None, buffer_size=65536):
+        self._pending_data_length = -1
         self._paused = True
         super().__init__(loop, sock, protocol, waiter, extra, server)
 
+        self._data = bytearray(buffer_size)
         self._loop.call_soon(self._loop_reading)
         self._paused = False
 
@@ -217,12 +218,12 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
         if self._read_fut is None:
             self._loop.call_soon(self._loop_reading, None)
 
-        data = self._pending_data
-        self._pending_data = None
-        if data is not None:
+        length = self._pending_data_length
+        self._pending_data_length = -1
+        if length > -1:
             # Call the protocol methode after calling _loop_reading(),
             # since the protocol can decide to pause reading again.
-            self._loop.call_soon(self._data_received, data)
+            self._loop.call_soon(self._data_received, self._data[:length], length)
 
         if self._loop.get_debug():
             logger.debug("%r resumes reading", self)
@@ -243,15 +244,15 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
         if not keep_open:
             self.close()
 
-    def _data_received(self, data):
+    def _data_received(self, data, length):
         if self._paused:
             # Don't call any protocol method while reading is paused.
             # The protocol will be called on resume_reading().
-            assert self._pending_data is None
-            self._pending_data = data
+            assert self._pending_data_length == -1
+            self._pending_data_length = length
             return
 
-        if not data:
+        if length == 0:
             self._eof_received()
             return
 
@@ -269,6 +270,7 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
             self._protocol.data_received(data)
 
     def _loop_reading(self, fut=None):
+        length = -1
         data = None
         try:
             if fut is not None:
@@ -277,18 +279,18 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
                 self._read_fut = None
                 if fut.done():
                     # deliver data later in "finally" clause
-                    data = fut.result()
+                    length = fut.result()
+                    if length == 0:
+                        # we got end-of-file so no need to reschedule a new read
+                        return
+
+                    data = self._data[:length]
                 else:
                     # the future will be replaced by next proactor.recv call
                     fut.cancel()
 
             if self._closing:
                 # since close() has been called we ignore any read data
-                data = None
-                return
-
-            if data == b'':
-                # we got end-of-file so no need to reschedule a new read
                 return
 
             # bpo-33694: buffer_updated() has currently no fast path because of
@@ -296,7 +298,7 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
 
             if not self._paused:
                 # reschedule a new read
-                self._read_fut = self._loop._proactor.recv(self._sock, 32768)
+                self._read_fut = self._loop._proactor.recv_into(self._sock, self._data)
         except ConnectionAbortedError as exc:
             if not self._closing:
                 self._fatal_error(exc, 'Fatal read error on pipe transport')
@@ -314,8 +316,8 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
             if not self._paused:
                 self._read_fut.add_done_callback(self._loop_reading)
         finally:
-            if data is not None:
-                self._data_received(data)
+            if length > -1:
+                self._data_received(data, length)
 
 
 class _ProactorBaseWritePipeTransport(_ProactorBasePipeTransport,