Use nonblocking sockets instead of selectors for healthy connections

This replaces the work in 3.2.0 to use nonblocking sockets instead of
selectors. Selectors proved to be problematic for some environments
including eventlet and gevent. Nonblocking sockets should be available
in all environments.

Author: andymccurdy

CHANGES

@@ -1,4 +1,4 @@
-* 3.2.2 (in development)
+* 3.3.0 (in development)
     * Resolve a race condition with the PubSubWorkerThread. #1150
     * Cleanup socket read error messages. Thanks Vic Yu. #1159
     * Cleanup the Connection's selector correctly. Thanks Bruce Merry. #1153
@@ -17,6 +17,9 @@
       cause the connection to be disconnected and cleaned up appropriately.
       #923
     * Add READONLY and READWRITE commands. Thanks @theodesp. #1114
+    * Remove selectors in favor of nonblocking sockets. Selectors had
+      issues in some environments including eventlet and gevent. This should
+      resolve those issues with no other side effects.
 * 3.2.1
     * Fix SentinelConnectionPool to work in multiprocess/forked environments.
 * 3.2.0

redis/__init__.py

@@ -29,7 +29,7 @@ def int_or_str(value):
         return value
 
 
-__version__ = '3.2.1'
+__version__ = '3.3.dev2'
 VERSION = tuple(map(int_or_str, __version__.split('.')))
 
 __all__ = [

redis/_compat.py

@@ -1,12 +1,12 @@
 """Internal module for Python 2 backwards compatibility."""
 import errno
+import socket
 import sys
 
 # For Python older than 3.5, retry EINTR.
 if sys.version_info[0] < 3 or (sys.version_info[0] == 3 and
                                sys.version_info[1] < 5):
     # Adapted from https://bugs.python.org/review/23863/patch/14532/54418
-    import socket
     import time
 
     # Wrapper for handling interruptable system calls.
@@ -100,6 +100,7 @@ def byte_to_chr(x):
     basestring = basestring
     unicode = unicode
     long = long
+    BlockingIOError = socket.error
 else:
     from urllib.parse import parse_qs, unquote, urlparse
     from string import ascii_letters
@@ -129,6 +130,7 @@ def nativestr(x):
     unicode = str
     safe_unicode = str
     long = int
+    BlockingIOError = BlockingIOError
 
 try:  # Python 3
     from queue import LifoQueue, Empty, Full

redis/connection.py

@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 from distutils.version import StrictVersion
+from errno import EWOULDBLOCK
 from itertools import chain
 import io
 import os
@@ -17,7 +18,7 @@
 from redis._compat import (xrange, imap, byte_to_chr, unicode, long,
                            nativestr, basestring, iteritems,
                            LifoQueue, Empty, Full, urlparse, parse_qs,
-                           recv, recv_into, unquote)
+                           recv, recv_into, unquote, BlockingIOError)
 from redis.exceptions import (
     DataError,
     RedisError,
@@ -31,7 +32,6 @@
     ExecAbortError,
     ReadOnlyError
 )
-from redis.selector import DefaultSelector
 from redis.utils import HIREDIS_AVAILABLE
 if HIREDIS_AVAILABLE:
     import hiredis
@@ -61,6 +61,8 @@
 
 SERVER_CLOSED_CONNECTION_ERROR = "Connection closed by server."
 
+SENTINEL = object()
+
 
 class Encoder(object):
     "Encode strings to bytes and decode bytes to strings"
@@ -126,9 +128,10 @@ def parse_error(self, response):
 
 
 class SocketBuffer(object):
-    def __init__(self, socket, socket_read_size):
+    def __init__(self, socket, socket_read_size, socket_timeout):
         self._sock = socket
         self.socket_read_size = socket_read_size
+        self.socket_timeout = socket_timeout
         self._buffer = io.BytesIO()
         # number of bytes written to the buffer from the socket
         self.bytes_written = 0
@@ -139,25 +142,51 @@ def __init__(self, socket, socket_read_size):
     def length(self):
         return self.bytes_written - self.bytes_read
 
-    def _read_from_socket(self, length=None):
+    def _read_from_socket(self, length=None, timeout=SENTINEL,
+                          raise_on_timeout=True):
+        sock = self._sock
         socket_read_size = self.socket_read_size
         buf = self._buffer
         buf.seek(self.bytes_written)
         marker = 0
+        custom_timeout = timeout is not SENTINEL
 
-        while True:
-            data = recv(self._sock, socket_read_size)
-            # an empty string indicates the server shutdown the socket
-            if isinstance(data, bytes) and len(data) == 0:
-                raise socket.error(SERVER_CLOSED_CONNECTION_ERROR)
-            buf.write(data)
-            data_length = len(data)
-            self.bytes_written += data_length
-            marker += data_length
-
-            if length is not None and length > marker:
-                continue
-            break
+        try:
+            if custom_timeout:
+                sock.settimeout(timeout)
+            while True:
+                data = recv(self._sock, socket_read_size)
+                # an empty string indicates the server shutdown the socket
+                if isinstance(data, bytes) and len(data) == 0:
+                    raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
+                buf.write(data)
+                data_length = len(data)
+                self.bytes_written += data_length
+                marker += data_length
+
+                if length is not None and length > marker:
+                    continue
+                return True
+        except BlockingIOError as ex:
+            # if we're in nonblocking mode and the recv raises a
+            # blocking error, simply return False indicating that
+            # there's no data to be read. otherwise raise the
+            # original exception.
+            if raise_on_timeout or ex.errno != EWOULDBLOCK:
+                raise
+            return False
+        except socket.timeout:
+            if raise_on_timeout:
+                raise
+            return False
+        finally:
+            if custom_timeout:
+                sock.settimeout(self.socket_timeout)
+
+    def can_read(self, timeout):
+        return bool(self.length) or \
+            self._read_from_socket(timeout=timeout,
+                                   raise_on_timeout=False)
 
     def read(self, length):
         length = length + 2  # make sure to read the \r\n terminator
@@ -233,7 +262,9 @@ def __del__(self):
     def on_connect(self, connection):
         "Called when the socket connects"
         self._sock = connection._sock
-        self._buffer = SocketBuffer(self._sock, self.socket_read_size)
+        self._buffer = SocketBuffer(self._sock,
+                                    self.socket_read_size,
+                                    connection.socket_timeout)
         self.encoder = connection.encoder
 
     def on_disconnect(self):
@@ -244,8 +275,8 @@ def on_disconnect(self):
             self._buffer = None
         self.encoder = None
 
-    def can_read(self):
-        return self._buffer and bool(self._buffer.length)
+    def can_read(self, timeout):
+        return self._buffer and self._buffer.can_read(timeout)
 
     def read_response(self):
         response = self._buffer.readline()
@@ -312,6 +343,7 @@ def __del__(self):
 
     def on_connect(self, connection):
         self._sock = connection._sock
+        self._socket_timeout = connection.socket_timeout
         kwargs = {
             'protocolError': InvalidResponse,
             'replyError': self.parse_error,
@@ -333,13 +365,52 @@ def on_disconnect(self):
         self._reader = None
         self._next_response = False
 
-    def can_read(self):
+    def can_read(self, timeout):
         if not self._reader:
             raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
 
         if self._next_response is False:
             self._next_response = self._reader.gets()
-        return self._next_response is not False
+            if self._next_response is False:
+                return self.read_from_socket(timeout=timeout,
+                                             raise_on_timeout=False)
+        return True
+
+    def read_from_socket(self, timeout=SENTINEL, raise_on_timeout=True):
+        sock = self._sock
+        custom_timeout = timeout is not SENTINEL
+        try:
+            if custom_timeout:
+                sock.settimeout(timeout)
+            if HIREDIS_USE_BYTE_BUFFER:
+                bufflen = recv_into(self._sock, self._buffer)
+                if bufflen == 0:
+                    raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
+                self._reader.feed(self._buffer, 0, bufflen)
+            else:
+                buffer = recv(self._sock, self.socket_read_size)
+                # an empty string indicates the server shutdown the socket
+                if not isinstance(buffer, bytes) or len(buffer) == 0:
+                    raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)
+                self._reader.feed(buffer)
+            # data was read from the socket and added to the buffer.
+            # return True to indicate that data was read.
+            return True
+        except BlockingIOError as ex:
+            # if we're in nonblocking mode and the recv raises a
+            # blocking error, simply return False indicating that
+            # there's no data to be read. otherwise raise the
+            # original exception.
+            if raise_on_timeout or ex.errno != EWOULDBLOCK:
+                raise
+            return False
+        except socket.timeout:
+            if not raise_on_timeout:
+                raise
+            return False
+        finally:
+            if custom_timeout:
+                sock.settimeout(self._socket_timeout)
 
     def read_response(self):
         if not self._reader:
@@ -352,21 +423,8 @@ def read_response(self):
             return response
 
         response = self._reader.gets()
-        socket_read_size = self.socket_read_size
         while response is False:
-            if HIREDIS_USE_BYTE_BUFFER:
-                bufflen = recv_into(self._sock, self._buffer)
-                if bufflen == 0:
-                    raise socket.error(SERVER_CLOSED_CONNECTION_ERROR)
-            else:
-                buffer = recv(self._sock, socket_read_size)
-                # an empty string indicates the server shutdown the socket
-                if not isinstance(buffer, bytes) or len(buffer) == 0:
-                    raise socket.error(SERVER_CLOSED_CONNECTION_ERROR)
-            if HIREDIS_USE_BYTE_BUFFER:
-                self._reader.feed(self._buffer, 0, bufflen)
-            else:
-                self._reader.feed(buffer)
+            self.read_from_socket()
             response = self._reader.gets()
         # if an older version of hiredis is installed, we need to attempt
         # to convert ResponseErrors to their appropriate types.
@@ -416,7 +474,6 @@ def __init__(self, host='localhost', port=6379, db=0, password=None,
         self.retry_on_timeout = retry_on_timeout
         self.encoder = Encoder(encoding, encoding_errors, decode_responses)
         self._sock = None
-        self._selector = None
         self._parser = parser_class(socket_read_size=socket_read_size)
         self._description_args = {
             'host': self.host,
@@ -454,7 +511,6 @@ def connect(self):
             raise ConnectionError(self._error_message(e))
 
         self._sock = sock
-        self._selector = DefaultSelector(sock)
         try:
             self.on_connect()
         except RedisError:
@@ -538,9 +594,6 @@ def disconnect(self):
         self._parser.on_disconnect()
         if self._sock is None:
             return
-        if self._selector is not None:
-            self._selector.close()
-            self._selector = None
         try:
             if os.getpid() == self.pid:
                 self._sock.shutdown(socket.SHUT_RDWR)
@@ -585,11 +638,7 @@ def can_read(self, timeout=0):
         if not sock:
             self.connect()
             sock = self._sock
-        return self._parser.can_read() or self._selector.can_read(timeout)
-
-    def is_ready_for_command(self):
-        "Check if the connection is ready for a command"
-        return self._selector.is_ready_for_command()
+        return self._parser.can_read(timeout)
 
     def read_response(self):
         "Read the response from a previously sent command"
@@ -963,10 +1012,13 @@ def get_connection(self, command_name, *keys, **options):
             # 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.
-            if not connection.is_ready_for_command():
+            try:
+                if connection.can_read():
+                    raise ConnectionError('Connection has data')
+            except ConnectionError:
                 connection.disconnect()
                 connection.connect()
-                if not connection.is_ready_for_command():
+                if connection.can_read():
                     raise ConnectionError('Connection not ready')
         except:  # noqa: E722
             # release the connection back to the pool so that we don't leak it
@@ -1111,10 +1163,13 @@ def get_connection(self, command_name, *keys, **options):
             # 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.
-            if not connection.is_ready_for_command():
+            try:
+                if connection.can_read():
+                    raise ConnectionError('Connection has data')
+            except ConnectionError:
                 connection.disconnect()
                 connection.connect()
-                if not connection.is_ready_for_command():
+                if connection.can_read():
                     raise ConnectionError('Connection not ready')
         except:  # noqa: E722
             # release the connection back to the pool so that we don't leak it