Tune the locking in ConnectionPool.get_connection

The lock does not need to be held while waiting for the socket to
establish and validate the TCP connection.

Author: andymccurdy

CHANGES

@@ -1,3 +1,7 @@
+* 3.5.2 (May 14, 2020)
+    * Tune the locking in ConnectionPool.get_connection so that the lock is
+      not held while waiting for the socket to establish and validate the
+      TCP connection.
 * 3.5.1 (May 9, 2020)
     * Fix for HSET argument validation to allow any non-None key. Thanks
       @AleksMat, #1337, #1341

redis/connection.py

@@ -1098,7 +1098,7 @@ def __repr__(self):
         )
 
     def reset(self):
-        self._lock = threading.RLock()
+        self._lock = threading.Lock()
         self._created_connections = 0
         self._available_connections = []
         self._in_use_connections = set()
@@ -1177,28 +1177,29 @@ def get_connection(self, command_name, *keys, **options):
             except IndexError:
                 connection = self.make_connection()
             self._in_use_connections.add(connection)
+
+        try:
+            # ensure this connection is connected to Redis
+            connection.connect()
+            # connections that the pool provides should be ready to send
+            # a command. if not, the connection was either returned to the
+            # pool before all data has been read or the socket has been
+            # closed. either way, reconnect and verify everything is good.
             try:
-                # ensure this connection is connected to Redis
+                if connection.can_read():
+                    raise ConnectionError('Connection has data')
+            except ConnectionError:
+                connection.disconnect()
                 connection.connect()
-                # connections that the pool provides should be ready to send
-                # a command. if not, the connection was either returned to the
-                # pool before all data has been read or the socket has been
-                # closed. either way, reconnect and verify everything is good.
-                try:
-                    if connection.can_read():
-                        raise ConnectionError('Connection has data')
-                except ConnectionError:
-                    connection.disconnect()
-                    connection.connect()
-                    if connection.can_read():
-                        raise ConnectionError('Connection not ready')
-            except BaseException:
-                # release the connection back to the pool so that we don't
-                # leak it
-                self.release(connection)
-                raise
-
-            return connection
+                if connection.can_read():
+                    raise ConnectionError('Connection not ready')
+        except BaseException:
+            # release the connection back to the pool so that we don't
+            # leak it
+            self.release(connection)
+            raise
+
+        return connection
 
     def get_encoder(self):
         "Return an encoder based on encoding settings"