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Edit File : connection.py \| Size : 30.94 KB
# # A higher level module for using sockets (or Windows named pipes) # # multiprocessing/connection.py # # Copyright (c) 2006-2008, R Oudkerk # Licensed to PSF under a Contributor Agreement. # __all__ = [ 'Client', 'Listener', 'Pipe', 'wait' ] import io import os import sys import socket import struct import time import tempfile import itertools import _multiprocessing from . import util from . import AuthenticationError, BufferTooShort from .context import reduction _ForkingPickler = reduction.ForkingPickler try: import _winapi from _winapi import WAIT_OBJECT_0, WAIT_ABANDONED_0, WAIT_TIMEOUT, INFINITE except ImportError: if sys.platform == 'win32': raise _winapi = None # # # BUFSIZE = 8192 # A very generous timeout when it comes to local connections... CONNECTION_TIMEOUT = 20. _mmap_counter = itertools.count() default_family = 'AF_INET' families = ['AF_INET'] if hasattr(socket, 'AF_UNIX'): default_family = 'AF_UNIX' families += ['AF_UNIX'] if sys.platform == 'win32': default_family = 'AF_PIPE' families += ['AF_PIPE'] def _init_timeout(timeout=CONNECTION_TIMEOUT): return time.monotonic() + timeout def _check_timeout(t): return time.monotonic() > t # # # def arbitrary_address(family): ''' Return an arbitrary free address for the given family ''' if family == 'AF_INET': return ('localhost', 0) elif family == 'AF_UNIX': return tempfile.mktemp(prefix='listener-', dir=util.get_temp_dir()) elif family == 'AF_PIPE': return tempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-' % (os.getpid(), next(_mmap_counter)), dir="") else: raise ValueError('unrecognized family') def _validate_family(family): ''' Checks if the family is valid for the current environment. ''' if sys.platform != 'win32' and family == 'AF_PIPE': raise ValueError('Family %s is not recognized.' % family) if sys.platform == 'win32' and family == 'AF_UNIX': # double check if not hasattr(socket, family): raise ValueError('Family %s is not recognized.' % family) def address_type(address): ''' Return the types of the address This can be 'AF_INET', 'AF_UNIX', or 'AF_PIPE' ''' if type(address) == tuple: return 'AF_INET' elif type(address) is str and address.startswith('\\\\'): return 'AF_PIPE' elif type(address) is str or util.is_abstract_socket_namespace(address): return 'AF_UNIX' else: raise ValueError('address type of %r unrecognized' % address) # # Connection classes # class _ConnectionBase: _handle = None def __init__(self, handle, readable=True, writable=True): handle = handle.__index__() if handle < 0: raise ValueError("invalid handle") if not readable and not writable: raise ValueError( "at least one of `readable` and `writable` must be True") self._handle = handle self._readable = readable self._writable = writable # XXX should we use util.Finalize instead of a __del__? def __del__(self): if self._handle is not None: self._close() def _check_closed(self): if self._handle is None: raise OSError("handle is closed") def _check_readable(self): if not self._readable: raise OSError("connection is write-only") def _check_writable(self): if not self._writable: raise OSError("connection is read-only") def _bad_message_length(self): if self._writable: self._readable = False else: self.close() raise OSError("bad message length") @property def closed(self): """True if the connection is closed""" return self._handle is None @property def readable(self): """True if the connection is readable""" return self._readable @property def writable(self): """True if the connection is writable""" return self._writable def fileno(self): """File descriptor or handle of the connection""" self._check_closed() return self._handle def close(self): """Close the connection""" if self._handle is not None: try: self._close() finally: self._handle = None def send_bytes(self, buf, offset=0, size=None): """Send the bytes data from a bytes-like object""" self._check_closed() self._check_writable() m = memoryview(buf) # HACK for byte-indexing of non-bytewise buffers (e.g. array.array) if m.itemsize > 1: m = memoryview(bytes(m)) n = len(m) if offset < 0: raise ValueError("offset is negative") if n < offset: raise ValueError("buffer length < offset") if size is None: size = n - offset elif size < 0: raise ValueError("size is negative") elif offset + size > n: raise ValueError("buffer length < offset + size") self._send_bytes(m[offset:offset + size]) def send(self, obj): """Send a (picklable) object""" self._check_closed() self._check_writable() self._send_bytes(_ForkingPickler.dumps(obj)) def recv_bytes(self, maxlength=None): """ Receive bytes data as a bytes object. """ self._check_closed() self._check_readable() if maxlength is not None and maxlength < 0: raise ValueError("negative maxlength") buf = self._recv_bytes(maxlength) if buf is None: self._bad_message_length() return buf.getvalue() def recv_bytes_into(self, buf, offset=0): """ Receive bytes data into a writeable bytes-like object. Return the number of bytes read. """ self._check_closed() self._check_readable() with memoryview(buf) as m: # Get bytesize of arbitrary buffer itemsize = m.itemsize bytesize = itemsize * len(m) if offset < 0: raise ValueError("negative offset") elif offset > bytesize: raise ValueError("offset too large") result = self._recv_bytes() size = result.tell() if bytesize < offset + size: raise BufferTooShort(result.getvalue()) # Message can fit in dest result.seek(0) result.readinto(m[offset // itemsize : (offset + size) // itemsize]) return size def recv(self): """Receive a (picklable) object""" self._check_closed() self._check_readable() buf = self._recv_bytes() return _ForkingPickler.loads(buf.getbuffer()) def poll(self, timeout=0.0): """Whether there is any input available to be read""" self._check_closed() self._check_readable() return self._poll(timeout) def __enter__(self): return self def __exit__(self, exc_type, exc_value, exc_tb): self.close() if _winapi: class PipeConnection(_ConnectionBase): """ Connection class based on a Windows named pipe. Overlapped I/O is used, so the handles must have been created with FILE_FLAG_OVERLAPPED. """ _got_empty_message = False def _close(self, _CloseHandle=_winapi.CloseHandle): _CloseHandle(self._handle) def _send_bytes(self, buf): ov, err = _winapi.WriteFile(self._handle, buf, overlapped=True) try: if err == _winapi.ERROR_IO_PENDING: waitres = _winapi.WaitForMultipleObjects( [ov.event], False, INFINITE) assert waitres == WAIT_OBJECT_0 except: ov.cancel() raise finally: nwritten, err = ov.GetOverlappedResult(True) assert err == 0 assert nwritten == len(buf) def _recv_bytes(self, maxsize=None): if self._got_empty_message: self._got_empty_message = False return io.BytesIO() else: bsize = 128 if maxsize is None else min(maxsize, 128) try: ov, err = _winapi.ReadFile(self._handle, bsize, overlapped=True) try: if err == _winapi.ERROR_IO_PENDING: waitres = _winapi.WaitForMultipleObjects( [ov.event], False, INFINITE) assert waitres == WAIT_OBJECT_0 except: ov.cancel() raise finally: nread, err = ov.GetOverlappedResult(True) if err == 0: f = io.BytesIO() f.write(ov.getbuffer()) return f elif err == _winapi.ERROR_MORE_DATA: return self._get_more_data(ov, maxsize) except OSError as e: if e.winerror == _winapi.ERROR_BROKEN_PIPE: raise EOFError else: raise raise RuntimeError("shouldn't get here; expected KeyboardInterrupt") def _poll(self, timeout): if (self._got_empty_message or _winapi.PeekNamedPipe(self._handle)[0] != 0): return True return bool(wait([self], timeout)) def _get_more_data(self, ov, maxsize): buf = ov.getbuffer() f = io.BytesIO() f.write(buf) left = _winapi.PeekNamedPipe(self._handle)[1] assert left > 0 if maxsize is not None and len(buf) + left > maxsize: self._bad_message_length() ov, err = _winapi.ReadFile(self._handle, left, overlapped=True) rbytes, err = ov.GetOverlappedResult(True) assert err == 0 assert rbytes == left f.write(ov.getbuffer()) return f class Connection(_ConnectionBase): """ Connection class based on an arbitrary file descriptor (Unix only), or a socket handle (Windows). """ if _winapi: def _close(self, _close=_multiprocessing.closesocket): _close(self._handle) _write = _multiprocessing.send _read = _multiprocessing.recv else: def _close(self, _close=os.close): _close(self._handle) _write = os.write _read = os.read def _send(self, buf, write=_write): remaining = len(buf) while True: n = write(self._handle, buf) remaining -= n if remaining == 0: break buf = buf[n:] def _recv(self, size, read=_read): buf = io.BytesIO() handle = self._handle remaining = size while remaining > 0: chunk = read(handle, remaining) n = len(chunk) if n == 0: if remaining == size: raise EOFError else: raise OSError("got end of file during message") buf.write(chunk) remaining -= n return buf def _send_bytes(self, buf): n = len(buf) if n > 0x7fffffff: pre_header = struct.pack("!i", -1) header = struct.pack("!Q", n) self._send(pre_header) self._send(header) self._send(buf) else: # For wire compatibility with 3.7 and lower header = struct.pack("!i", n) if n > 16384: # The payload is large so Nagle's algorithm won't be triggered # and we'd better avoid the cost of concatenation. self._send(header) self._send(buf) else: # Issue #20540: concatenate before sending, to avoid delays due # to Nagle's algorithm on a TCP socket. # Also note we want to avoid sending a 0-length buffer separately, # to avoid "broken pipe" errors if the other end closed the pipe. self._send(header + buf) def _recv_bytes(self, maxsize=None): buf = self._recv(4) size, = struct.unpack("!i", buf.getvalue()) if size == -1: buf = self._recv(8) size, = struct.unpack("!Q", buf.getvalue()) if maxsize is not None and size > maxsize: return None return self._recv(size) def _poll(self, timeout): r = wait([self], timeout) return bool(r) # # Public functions # class Listener(object): ''' Returns a listener object. This is a wrapper for a bound socket which is 'listening' for connections, or for a Windows named pipe. ''' def __init__(self, address=None, family=None, backlog=1, authkey=None): family = family or (address and address_type(address)) \ or default_family address = address or arbitrary_address(family) _validate_family(family) if family == 'AF_PIPE': self._listener = PipeListener(address, backlog) else: self._listener = SocketListener(address, family, backlog) if authkey is not None and not isinstance(authkey, bytes): raise TypeError('authkey should be a byte string') self._authkey = authkey def accept(self): ''' Accept a connection on the bound socket or named pipe of `self`. Returns a `Connection` object. ''' if self._listener is None: raise OSError('listener is closed') c = self._listener.accept() if self._authkey: deliver_challenge(c, self._authkey) answer_challenge(c, self._authkey) return c def close(self): ''' Close the bound socket or named pipe of `self`. ''' listener = self._listener if listener is not None: self._listener = None listener.close() @property def address(self): return self._listener._address @property def last_accepted(self): return self._listener._last_accepted def __enter__(self): return self def __exit__(self, exc_type, exc_value, exc_tb): self.close() def Client(address, family=None, authkey=None): ''' Returns a connection to the address of a `Listener` ''' family = family or address_type(address) _validate_family(family) if family == 'AF_PIPE': c = PipeClient(address) else: c = SocketClient(address) if authkey is not None and not isinstance(authkey, bytes): raise TypeError('authkey should be a byte string') if authkey is not None: answer_challenge(c, authkey) deliver_challenge(c, authkey) return c if sys.platform != 'win32': def Pipe(duplex=True): ''' Returns pair of connection objects at either end of a pipe ''' if duplex: s1, s2 = socket.socketpair() s1.setblocking(True) s2.setblocking(True) c1 = Connection(s1.detach()) c2 = Connection(s2.detach()) else: fd1, fd2 = os.pipe() c1 = Connection(fd1, writable=False) c2 = Connection(fd2, readable=False) return c1, c2 else: def Pipe(duplex=True): ''' Returns pair of connection objects at either end of a pipe ''' address = arbitrary_address('AF_PIPE') if duplex: openmode = _winapi.PIPE_ACCESS_DUPLEX access = _winapi.GENERIC_READ \| _winapi.GENERIC_WRITE obsize, ibsize = BUFSIZE, BUFSIZE else: openmode = _winapi.PIPE_ACCESS_INBOUND access = _winapi.GENERIC_WRITE obsize, ibsize = 0, BUFSIZE h1 = _winapi.CreateNamedPipe( address, openmode \| _winapi.FILE_FLAG_OVERLAPPED \| _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE, _winapi.PIPE_TYPE_MESSAGE \| _winapi.PIPE_READMODE_MESSAGE \| _winapi.PIPE_WAIT, 1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER, # default security descriptor: the handle cannot be inherited _winapi.NULL ) h2 = _winapi.CreateFile( address, access, 0, _winapi.NULL, _winapi.OPEN_EXISTING, _winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL ) _winapi.SetNamedPipeHandleState( h2, _winapi.PIPE_READMODE_MESSAGE, None, None ) overlapped = _winapi.ConnectNamedPipe(h1, overlapped=True) _, err = overlapped.GetOverlappedResult(True) assert err == 0 c1 = PipeConnection(h1, writable=duplex) c2 = PipeConnection(h2, readable=duplex) return c1, c2 # # Definitions for connections based on sockets # class SocketListener(object): ''' Representation of a socket which is bound to an address and listening ''' def __init__(self, address, family, backlog=1): self._socket = socket.socket(getattr(socket, family)) try: # SO_REUSEADDR has different semantics on Windows (issue #2550). if os.name == 'posix': self._socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) self._socket.setblocking(True) self._socket.bind(address) self._socket.listen(backlog) self._address = self._socket.getsockname() except OSError: self._socket.close() raise self._family = family self._last_accepted = None if family == 'AF_UNIX' and not util.is_abstract_socket_namespace(address): # Linux abstract socket namespaces do not need to be explicitly unlinked self._unlink = util.Finalize( self, os.unlink, args=(address,), exitpriority=0 ) else: self._unlink = None def accept(self): s, self._last_accepted = self._socket.accept() s.setblocking(True) return Connection(s.detach()) def close(self): try: self._socket.close() finally: unlink = self._unlink if unlink is not None: self._unlink = None unlink() def SocketClient(address): ''' Return a connection object connected to the socket given by `address` ''' family = address_type(address) with socket.socket( getattr(socket, family) ) as s: s.setblocking(True) s.connect(address) return Connection(s.detach()) # # Definitions for connections based on named pipes # if sys.platform == 'win32': class PipeListener(object): ''' Representation of a named pipe ''' def __init__(self, address, backlog=None): self._address = address self._handle_queue = [self._new_handle(first=True)] self._last_accepted = None util.sub_debug('listener created with address=%r', self._address) self.close = util.Finalize( self, PipeListener._finalize_pipe_listener, args=(self._handle_queue, self._address), exitpriority=0 ) def _new_handle(self, first=False): flags = _winapi.PIPE_ACCESS_DUPLEX \| _winapi.FILE_FLAG_OVERLAPPED if first: flags \|= _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE return _winapi.CreateNamedPipe( self._address, flags, _winapi.PIPE_TYPE_MESSAGE \| _winapi.PIPE_READMODE_MESSAGE \| _winapi.PIPE_WAIT, _winapi.PIPE_UNLIMITED_INSTANCES, BUFSIZE, BUFSIZE, _winapi.NMPWAIT_WAIT_FOREVER, _winapi.NULL ) def accept(self): self._handle_queue.append(self._new_handle()) handle = self._handle_queue.pop(0) try: ov = _winapi.ConnectNamedPipe(handle, overlapped=True) except OSError as e: if e.winerror != _winapi.ERROR_NO_DATA: raise # ERROR_NO_DATA can occur if a client has already connected, # written data and then disconnected -- see Issue 14725. else: try: res = _winapi.WaitForMultipleObjects( [ov.event], False, INFINITE) except: ov.cancel() _winapi.CloseHandle(handle) raise finally: _, err = ov.GetOverlappedResult(True) assert err == 0 return PipeConnection(handle) @staticmethod def _finalize_pipe_listener(queue, address): util.sub_debug('closing listener with address=%r', address) for handle in queue: _winapi.CloseHandle(handle) def PipeClient(address): ''' Return a connection object connected to the pipe given by `address` ''' t = _init_timeout() while 1: try: _winapi.WaitNamedPipe(address, 1000) h = _winapi.CreateFile( address, _winapi.GENERIC_READ \| _winapi.GENERIC_WRITE, 0, _winapi.NULL, _winapi.OPEN_EXISTING, _winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL ) except OSError as e: if e.winerror not in (_winapi.ERROR_SEM_TIMEOUT, _winapi.ERROR_PIPE_BUSY) or _check_timeout(t): raise else: break else: raise _winapi.SetNamedPipeHandleState( h, _winapi.PIPE_READMODE_MESSAGE, None, None ) return PipeConnection(h) # # Authentication stuff # MESSAGE_LENGTH = 20 CHALLENGE = b'#CHALLENGE#' WELCOME = b'#WELCOME#' FAILURE = b'#FAILURE#' def deliver_challenge(connection, authkey): import hmac if not isinstance(authkey, bytes): raise ValueError( "Authkey must be bytes, not {0!s}".format(type(authkey))) message = os.urandom(MESSAGE_LENGTH) connection.send_bytes(CHALLENGE + message) digest = hmac.new(authkey, message, 'md5').digest() response = connection.recv_bytes(256) # reject large message if response == digest: connection.send_bytes(WELCOME) else: connection.send_bytes(FAILURE) raise AuthenticationError('digest received was wrong') def answer_challenge(connection, authkey): import hmac if not isinstance(authkey, bytes): raise ValueError( "Authkey must be bytes, not {0!s}".format(type(authkey))) message = connection.recv_bytes(256) # reject large message assert message[:len(CHALLENGE)] == CHALLENGE, 'message = %r' % message message = message[len(CHALLENGE):] digest = hmac.new(authkey, message, 'md5').digest() connection.send_bytes(digest) response = connection.recv_bytes(256) # reject large message if response != WELCOME: raise AuthenticationError('digest sent was rejected') # # Support for using xmlrpclib for serialization # class ConnectionWrapper(object): def __init__(self, conn, dumps, loads): self._conn = conn self._dumps = dumps self._loads = loads for attr in ('fileno', 'close', 'poll', 'recv_bytes', 'send_bytes'): obj = getattr(conn, attr) setattr(self, attr, obj) def send(self, obj): s = self._dumps(obj) self._conn.send_bytes(s) def recv(self): s = self._conn.recv_bytes() return self._loads(s) def _xml_dumps(obj): return xmlrpclib.dumps((obj,), None, None, None, 1).encode('utf-8') def _xml_loads(s): (obj,), method = xmlrpclib.loads(s.decode('utf-8')) return obj class XmlListener(Listener): def accept(self): global xmlrpclib import xmlrpc.client as xmlrpclib obj = Listener.accept(self) return ConnectionWrapper(obj, _xml_dumps, _xml_loads) def XmlClient(args, kwds): global xmlrpclib import xmlrpc.client as xmlrpclib return ConnectionWrapper(Client(args, *kwds), _xml_dumps, _xml_loads) # # Wait # if sys.platform == 'win32': def _exhaustive_wait(handles, timeout): # Return ALL handles which are currently signalled. (Only # returning the first signalled might create starvation issues.) L = list(handles) ready = [] while L: res = _winapi.WaitForMultipleObjects(L, False, timeout) if res == WAIT_TIMEOUT: break elif WAIT_OBJECT_0 <= res < WAIT_OBJECT_0 + len(L): res -= WAIT_OBJECT_0 elif WAIT_ABANDONED_0 <= res < WAIT_ABANDONED_0 + len(L): res -= WAIT_ABANDONED_0 else: raise RuntimeError('Should not get here') ready.append(L[res]) L = L[res+1:] timeout = 0 return ready _ready_errors = {_winapi.ERROR_BROKEN_PIPE, _winapi.ERROR_NETNAME_DELETED} def wait(object_list, timeout=None): ''' Wait till an object in object_list is ready/readable. Returns list of those objects in object_list which are ready/readable. ''' if timeout is None: timeout = INFINITE elif timeout < 0: timeout = 0 else: timeout = int(timeout 1000 + 0.5) object_list = list(object_list) waithandle_to_obj = {} ov_list = [] ready_objects = set() ready_handles = set() try: for o in object_list: try: fileno = getattr(o, 'fileno') except AttributeError: waithandle_to_obj[o.__index__()] = o else: # start an overlapped read of length zero try: ov, err = _winapi.ReadFile(fileno(), 0, True) except OSError as e: ov, err = None, e.winerror if err not in _ready_errors: raise if err == _winapi.ERROR_IO_PENDING: ov_list.append(ov) waithandle_to_obj[ov.event] = o else: # If o.fileno() is an overlapped pipe handle and # err == 0 then there is a zero length message # in the pipe, but it HAS NOT been consumed... if ov and sys.getwindowsversion()[:2] >= (6, 2): # ... except on Windows 8 and later, where # the message HAS been consumed. try: _, err = ov.GetOverlappedResult(False) except OSError as e: err = e.winerror if not err and hasattr(o, '_got_empty_message'): o._got_empty_message = True ready_objects.add(o) timeout = 0 ready_handles = _exhaustive_wait(waithandle_to_obj.keys(), timeout) finally: # request that overlapped reads stop for ov in ov_list: ov.cancel() # wait for all overlapped reads to stop for ov in ov_list: try: _, err = ov.GetOverlappedResult(True) except OSError as e: err = e.winerror if err not in _ready_errors: raise if err != _winapi.ERROR_OPERATION_ABORTED: o = waithandle_to_obj[ov.event] ready_objects.add(o) if err == 0: # If o.fileno() is an overlapped pipe handle then # a zero length message HAS been consumed. if hasattr(o, '_got_empty_message'): o._got_empty_message = True ready_objects.update(waithandle_to_obj[h] for h in ready_handles) return [o for o in object_list if o in ready_objects] else: import selectors # poll/select have the advantage of not requiring any extra file # descriptor, contrarily to epoll/kqueue (also, they require a single # syscall). if hasattr(selectors, 'PollSelector'): _WaitSelector = selectors.PollSelector else: _WaitSelector = selectors.SelectSelector def wait(object_list, timeout=None): ''' Wait till an object in object_list is ready/readable. Returns list of those objects in object_list which are ready/readable. ''' with _WaitSelector() as selector: for obj in object_list: selector.register(obj, selectors.EVENT_READ) if timeout is not None: deadline = time.monotonic() + timeout while True: ready = selector.select(timeout) if ready: return [key.fileobj for (key, events) in ready] else: if timeout is not None: timeout = deadline - time.monotonic() if timeout < 0: return ready # # Make connection and socket objects sharable if possible # if sys.platform == 'win32': def reduce_connection(conn): handle = conn.fileno() with socket.fromfd(handle, socket.AF_INET, socket.SOCK_STREAM) as s: from . import resource_sharer ds = resource_sharer.DupSocket(s) return rebuild_connection, (ds, conn.readable, conn.writable) def rebuild_connection(ds, readable, writable): sock = ds.detach() return Connection(sock.detach(), readable, writable) reduction.register(Connection, reduce_connection) def reduce_pipe_connection(conn): access = ((_winapi.FILE_GENERIC_READ if conn.readable else 0) \| (_winapi.FILE_GENERIC_WRITE if conn.writable else 0)) dh = reduction.DupHandle(conn.fileno(), access) return rebuild_pipe_connection, (dh, conn.readable, conn.writable) def rebuild_pipe_connection(dh, readable, writable): handle = dh.detach() return PipeConnection(handle, readable, writable) reduction.register(PipeConnection, reduce_pipe_connection) else: def reduce_connection(conn): df = reduction.DupFd(conn.fileno()) return rebuild_connection, (df, conn.readable, conn.writable) def rebuild_connection(df, readable, writable): fd = df.detach() return Connection(fd, readable, writable) reduction.register(Connection, reduce_connection) Back

Edit File : connection.py | Size : 30.94 KB

#
# A higher level module for using sockets (or Windows named pipes)
#
# multiprocessing/connection.py
#
# Copyright (c) 2006-2008, R Oudkerk
# Licensed to PSF under a Contributor Agreement.
#

__all__ = [ 'Client', 'Listener', 'Pipe', 'wait' ]

import io
import os
import sys
import socket
import struct
import time
import tempfile
import itertools

import _multiprocessing

from . import util

from . import AuthenticationError, BufferTooShort
from .context import reduction
_ForkingPickler = reduction.ForkingPickler

try:
    import _winapi
    from _winapi import WAIT_OBJECT_0, WAIT_ABANDONED_0, WAIT_TIMEOUT, INFINITE
except ImportError:
    if sys.platform == 'win32':
        raise
    _winapi = None

#
#
#

BUFSIZE = 8192
# A very generous timeout when it comes to local connections...
CONNECTION_TIMEOUT = 20.

_mmap_counter = itertools.count()

default_family = 'AF_INET'
families = ['AF_INET']

if hasattr(socket, 'AF_UNIX'):
    default_family = 'AF_UNIX'
    families += ['AF_UNIX']

if sys.platform == 'win32':
    default_family = 'AF_PIPE'
    families += ['AF_PIPE']

def _init_timeout(timeout=CONNECTION_TIMEOUT):
    return time.monotonic() + timeout

def _check_timeout(t):
    return time.monotonic() > t

#
#
#

def arbitrary_address(family):
    '''
    Return an arbitrary free address for the given family
    '''
    if family == 'AF_INET':
        return ('localhost', 0)
    elif family == 'AF_UNIX':
        return tempfile.mktemp(prefix='listener-', dir=util.get_temp_dir())
    elif family == 'AF_PIPE':
        return tempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-' %
                               (os.getpid(), next(_mmap_counter)), dir="")
    else:
        raise ValueError('unrecognized family')

def _validate_family(family):
    '''
    Checks if the family is valid for the current environment.
    '''
    if sys.platform != 'win32' and family == 'AF_PIPE':
        raise ValueError('Family %s is not recognized.' % family)

if sys.platform == 'win32' and family == 'AF_UNIX':
        # double check
        if not hasattr(socket, family):
            raise ValueError('Family %s is not recognized.' % family)

def address_type(address):
    '''
    Return the types of the address

This can be 'AF_INET', 'AF_UNIX', or 'AF_PIPE'
    '''
    if type(address) == tuple:
        return 'AF_INET'
    elif type(address) is str and address.startswith('\\\\'):
        return 'AF_PIPE'
    elif type(address) is str or util.is_abstract_socket_namespace(address):
        return 'AF_UNIX'
    else:
        raise ValueError('address type of %r unrecognized' % address)

#
# Connection classes
#

class _ConnectionBase:
    _handle = None

def __init__(self, handle, readable=True, writable=True):
        handle = handle.__index__()
        if handle < 0:
            raise ValueError("invalid handle")
        if not readable and not writable:
            raise ValueError(
                "at least one of `readable` and `writable` must be True")
        self._handle = handle
        self._readable = readable
        self._writable = writable

# XXX should we use util.Finalize instead of a __del__?

def __del__(self):
        if self._handle is not None:
            self._close()

def _check_closed(self):
        if self._handle is None:
            raise OSError("handle is closed")

def _check_readable(self):
        if not self._readable:
            raise OSError("connection is write-only")

def _check_writable(self):
        if not self._writable:
            raise OSError("connection is read-only")

def _bad_message_length(self):
        if self._writable:
            self._readable = False
        else:
            self.close()
        raise OSError("bad message length")

@property
    def closed(self):
        """True if the connection is closed"""
        return self._handle is None

@property
    def readable(self):
        """True if the connection is readable"""
        return self._readable

@property
    def writable(self):
        """True if the connection is writable"""
        return self._writable

def fileno(self):
        """File descriptor or handle of the connection"""
        self._check_closed()
        return self._handle

def close(self):
        """Close the connection"""
        if self._handle is not None:
            try:
                self._close()
            finally:
                self._handle = None

def send_bytes(self, buf, offset=0, size=None):
        """Send the bytes data from a bytes-like object"""
        self._check_closed()
        self._check_writable()
        m = memoryview(buf)
        # HACK for byte-indexing of non-bytewise buffers (e.g. array.array)
        if m.itemsize > 1:
            m = memoryview(bytes(m))
        n = len(m)
        if offset < 0:
            raise ValueError("offset is negative")
        if n < offset:
            raise ValueError("buffer length < offset")
        if size is None:
            size = n - offset
        elif size < 0:
            raise ValueError("size is negative")
        elif offset + size > n:
            raise ValueError("buffer length < offset + size")
        self._send_bytes(m[offset:offset + size])

def send(self, obj):
        """Send a (picklable) object"""
        self._check_closed()
        self._check_writable()
        self._send_bytes(_ForkingPickler.dumps(obj))

def recv_bytes(self, maxlength=None):
        """
        Receive bytes data as a bytes object.
        """
        self._check_closed()
        self._check_readable()
        if maxlength is not None and maxlength < 0:
            raise ValueError("negative maxlength")
        buf = self._recv_bytes(maxlength)
        if buf is None:
            self._bad_message_length()
        return buf.getvalue()

def recv_bytes_into(self, buf, offset=0):
        """
        Receive bytes data into a writeable bytes-like object.
        Return the number of bytes read.
        """
        self._check_closed()
        self._check_readable()
        with memoryview(buf) as m:
            # Get bytesize of arbitrary buffer
            itemsize = m.itemsize
            bytesize = itemsize * len(m)
            if offset < 0:
                raise ValueError("negative offset")
            elif offset > bytesize:
                raise ValueError("offset too large")
            result = self._recv_bytes()
            size = result.tell()
            if bytesize < offset + size:
                raise BufferTooShort(result.getvalue())
            # Message can fit in dest
            result.seek(0)
            result.readinto(m[offset // itemsize :
                              (offset + size) // itemsize])
            return size

def recv(self):
        """Receive a (picklable) object"""
        self._check_closed()
        self._check_readable()
        buf = self._recv_bytes()
        return _ForkingPickler.loads(buf.getbuffer())

def poll(self, timeout=0.0):
        """Whether there is any input available to be read"""
        self._check_closed()
        self._check_readable()
        return self._poll(timeout)

def __enter__(self):
        return self

def __exit__(self, exc_type, exc_value, exc_tb):
        self.close()

if _winapi:

class PipeConnection(_ConnectionBase):
        """
        Connection class based on a Windows named pipe.
        Overlapped I/O is used, so the handles must have been created
        with FILE_FLAG_OVERLAPPED.
        """
        _got_empty_message = False

def _close(self, _CloseHandle=_winapi.CloseHandle):
            _CloseHandle(self._handle)

def _send_bytes(self, buf):
            ov, err = _winapi.WriteFile(self._handle, buf, overlapped=True)
            try:
                if err == _winapi.ERROR_IO_PENDING:
                    waitres = _winapi.WaitForMultipleObjects(
                        [ov.event], False, INFINITE)
                    assert waitres == WAIT_OBJECT_0
            except:
                ov.cancel()
                raise
            finally:
                nwritten, err = ov.GetOverlappedResult(True)
            assert err == 0
            assert nwritten == len(buf)

def _recv_bytes(self, maxsize=None):
            if self._got_empty_message:
                self._got_empty_message = False
                return io.BytesIO()
            else:
                bsize = 128 if maxsize is None else min(maxsize, 128)
                try:
                    ov, err = _winapi.ReadFile(self._handle, bsize,
                                                overlapped=True)
                    try:
                        if err == _winapi.ERROR_IO_PENDING:
                            waitres = _winapi.WaitForMultipleObjects(
                                [ov.event], False, INFINITE)
                            assert waitres == WAIT_OBJECT_0
                    except:
                        ov.cancel()
                        raise
                    finally:
                        nread, err = ov.GetOverlappedResult(True)
                        if err == 0:
                            f = io.BytesIO()
                            f.write(ov.getbuffer())
                            return f
                        elif err == _winapi.ERROR_MORE_DATA:
                            return self._get_more_data(ov, maxsize)
                except OSError as e:
                    if e.winerror == _winapi.ERROR_BROKEN_PIPE:
                        raise EOFError
                    else:
                        raise
            raise RuntimeError("shouldn't get here; expected KeyboardInterrupt")

def _poll(self, timeout):
            if (self._got_empty_message or
                        _winapi.PeekNamedPipe(self._handle)[0] != 0):
                return True
            return bool(wait([self], timeout))

def _get_more_data(self, ov, maxsize):
            buf = ov.getbuffer()
            f = io.BytesIO()
            f.write(buf)
            left = _winapi.PeekNamedPipe(self._handle)[1]
            assert left > 0
            if maxsize is not None and len(buf) + left > maxsize:
                self._bad_message_length()
            ov, err = _winapi.ReadFile(self._handle, left, overlapped=True)
            rbytes, err = ov.GetOverlappedResult(True)
            assert err == 0
            assert rbytes == left
            f.write(ov.getbuffer())
            return f

class Connection(_ConnectionBase):
    """
    Connection class based on an arbitrary file descriptor (Unix only), or
    a socket handle (Windows).
    """

if _winapi:
        def _close(self, _close=_multiprocessing.closesocket):
            _close(self._handle)
        _write = _multiprocessing.send
        _read = _multiprocessing.recv
    else:
        def _close(self, _close=os.close):
            _close(self._handle)
        _write = os.write
        _read = os.read

def _send(self, buf, write=_write):
        remaining = len(buf)
        while True:
            n = write(self._handle, buf)
            remaining -= n
            if remaining == 0:
                break
            buf = buf[n:]

def _recv(self, size, read=_read):
        buf = io.BytesIO()
        handle = self._handle
        remaining = size
        while remaining > 0:
            chunk = read(handle, remaining)
            n = len(chunk)
            if n == 0:
                if remaining == size:
                    raise EOFError
                else:
                    raise OSError("got end of file during message")
            buf.write(chunk)
            remaining -= n
        return buf

def _send_bytes(self, buf):
        n = len(buf)
        if n > 0x7fffffff:
            pre_header = struct.pack("!i", -1)
            header = struct.pack("!Q", n)
            self._send(pre_header)
            self._send(header)
            self._send(buf)
        else:
            # For wire compatibility with 3.7 and lower
            header = struct.pack("!i", n)
            if n > 16384:
                # The payload is large so Nagle's algorithm won't be triggered
                # and we'd better avoid the cost of concatenation.
                self._send(header)
                self._send(buf)
            else:
                # Issue #20540: concatenate before sending, to avoid delays due
                # to Nagle's algorithm on a TCP socket.
                # Also note we want to avoid sending a 0-length buffer separately,
                # to avoid "broken pipe" errors if the other end closed the pipe.
                self._send(header + buf)

def _recv_bytes(self, maxsize=None):
        buf = self._recv(4)
        size, = struct.unpack("!i", buf.getvalue())
        if size == -1:
            buf = self._recv(8)
            size, = struct.unpack("!Q", buf.getvalue())
        if maxsize is not None and size > maxsize:
            return None
        return self._recv(size)

def _poll(self, timeout):
        r = wait([self], timeout)
        return bool(r)

#
# Public functions
#

class Listener(object):
    '''
    Returns a listener object.

This is a wrapper for a bound socket which is 'listening' for
    connections, or for a Windows named pipe.
    '''
    def __init__(self, address=None, family=None, backlog=1, authkey=None):
        family = family or (address and address_type(address)) \
                 or default_family
        address = address or arbitrary_address(family)

_validate_family(family)
        if family == 'AF_PIPE':
            self._listener = PipeListener(address, backlog)
        else:
            self._listener = SocketListener(address, family, backlog)

if authkey is not None and not isinstance(authkey, bytes):
            raise TypeError('authkey should be a byte string')

self._authkey = authkey

def accept(self):
        '''
        Accept a connection on the bound socket or named pipe of `self`.

Returns a `Connection` object.
        '''
        if self._listener is None:
            raise OSError('listener is closed')
        c = self._listener.accept()
        if self._authkey:
            deliver_challenge(c, self._authkey)
            answer_challenge(c, self._authkey)
        return c

def close(self):
        '''
        Close the bound socket or named pipe of `self`.
        '''
        listener = self._listener
        if listener is not None:
            self._listener = None
            listener.close()

@property
    def address(self):
        return self._listener._address

@property
    def last_accepted(self):
        return self._listener._last_accepted

def __enter__(self):
        return self

def __exit__(self, exc_type, exc_value, exc_tb):
        self.close()

def Client(address, family=None, authkey=None):
    '''
    Returns a connection to the address of a `Listener`
    '''
    family = family or address_type(address)
    _validate_family(family)
    if family == 'AF_PIPE':
        c = PipeClient(address)
    else:
        c = SocketClient(address)

if authkey is not None and not isinstance(authkey, bytes):
        raise TypeError('authkey should be a byte string')

if authkey is not None:
        answer_challenge(c, authkey)
        deliver_challenge(c, authkey)

return c

if sys.platform != 'win32':

def Pipe(duplex=True):
        '''
        Returns pair of connection objects at either end of a pipe
        '''
        if duplex:
            s1, s2 = socket.socketpair()
            s1.setblocking(True)
            s2.setblocking(True)
            c1 = Connection(s1.detach())
            c2 = Connection(s2.detach())
        else:
            fd1, fd2 = os.pipe()
            c1 = Connection(fd1, writable=False)
            c2 = Connection(fd2, readable=False)

return c1, c2

else:

def Pipe(duplex=True):
        '''
        Returns pair of connection objects at either end of a pipe
        '''
        address = arbitrary_address('AF_PIPE')
        if duplex:
            openmode = _winapi.PIPE_ACCESS_DUPLEX
            access = _winapi.GENERIC_READ | _winapi.GENERIC_WRITE
            obsize, ibsize = BUFSIZE, BUFSIZE
        else:
            openmode = _winapi.PIPE_ACCESS_INBOUND
            access = _winapi.GENERIC_WRITE
            obsize, ibsize = 0, BUFSIZE

h1 = _winapi.CreateNamedPipe(
            address, openmode | _winapi.FILE_FLAG_OVERLAPPED |
            _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE,
            _winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_READMODE_MESSAGE |
            _winapi.PIPE_WAIT,
            1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER,
            # default security descriptor: the handle cannot be inherited
            _winapi.NULL
            )
        h2 = _winapi.CreateFile(
            address, access, 0, _winapi.NULL, _winapi.OPEN_EXISTING,
            _winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL
            )
        _winapi.SetNamedPipeHandleState(
            h2, _winapi.PIPE_READMODE_MESSAGE, None, None
            )

overlapped = _winapi.ConnectNamedPipe(h1, overlapped=True)
        _, err = overlapped.GetOverlappedResult(True)
        assert err == 0

c1 = PipeConnection(h1, writable=duplex)
        c2 = PipeConnection(h2, readable=duplex)

return c1, c2

#
# Definitions for connections based on sockets
#

class SocketListener(object):
    '''
    Representation of a socket which is bound to an address and listening
    '''
    def __init__(self, address, family, backlog=1):
        self._socket = socket.socket(getattr(socket, family))
        try:
            # SO_REUSEADDR has different semantics on Windows (issue #2550).
            if os.name == 'posix':
                self._socket.setsockopt(socket.SOL_SOCKET,
                                        socket.SO_REUSEADDR, 1)
            self._socket.setblocking(True)
            self._socket.bind(address)
            self._socket.listen(backlog)
            self._address = self._socket.getsockname()
        except OSError:
            self._socket.close()
            raise
        self._family = family
        self._last_accepted = None

if family == 'AF_UNIX' and not util.is_abstract_socket_namespace(address):
            # Linux abstract socket namespaces do not need to be explicitly unlinked
            self._unlink = util.Finalize(
                self, os.unlink, args=(address,), exitpriority=0
                )
        else:
            self._unlink = None

def accept(self):
        s, self._last_accepted = self._socket.accept()
        s.setblocking(True)
        return Connection(s.detach())

def close(self):
        try:
            self._socket.close()
        finally:
            unlink = self._unlink
            if unlink is not None:
                self._unlink = None
                unlink()

def SocketClient(address):
    '''
    Return a connection object connected to the socket given by `address`
    '''
    family = address_type(address)
    with socket.socket( getattr(socket, family) ) as s:
        s.setblocking(True)
        s.connect(address)
        return Connection(s.detach())

#
# Definitions for connections based on named pipes
#

if sys.platform == 'win32':

class PipeListener(object):
        '''
        Representation of a named pipe
        '''
        def __init__(self, address, backlog=None):
            self._address = address
            self._handle_queue = [self._new_handle(first=True)]

self._last_accepted = None
            util.sub_debug('listener created with address=%r', self._address)
            self.close = util.Finalize(
                self, PipeListener._finalize_pipe_listener,
                args=(self._handle_queue, self._address), exitpriority=0
                )

def _new_handle(self, first=False):
            flags = _winapi.PIPE_ACCESS_DUPLEX | _winapi.FILE_FLAG_OVERLAPPED
            if first:
                flags |= _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE
            return _winapi.CreateNamedPipe(
                self._address, flags,
                _winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_READMODE_MESSAGE |
                _winapi.PIPE_WAIT,
                _winapi.PIPE_UNLIMITED_INSTANCES, BUFSIZE, BUFSIZE,
                _winapi.NMPWAIT_WAIT_FOREVER, _winapi.NULL
                )

def accept(self):
            self._handle_queue.append(self._new_handle())
            handle = self._handle_queue.pop(0)
            try:
                ov = _winapi.ConnectNamedPipe(handle, overlapped=True)
            except OSError as e:
                if e.winerror != _winapi.ERROR_NO_DATA:
                    raise
                # ERROR_NO_DATA can occur if a client has already connected,
                # written data and then disconnected -- see Issue 14725.
            else:
                try:
                    res = _winapi.WaitForMultipleObjects(
                        [ov.event], False, INFINITE)
                except:
                    ov.cancel()
                    _winapi.CloseHandle(handle)
                    raise
                finally:
                    _, err = ov.GetOverlappedResult(True)
                    assert err == 0
            return PipeConnection(handle)

@staticmethod
        def _finalize_pipe_listener(queue, address):
            util.sub_debug('closing listener with address=%r', address)
            for handle in queue:
                _winapi.CloseHandle(handle)

def PipeClient(address):
        '''
        Return a connection object connected to the pipe given by `address`
        '''
        t = _init_timeout()
        while 1:
            try:
                _winapi.WaitNamedPipe(address, 1000)
                h = _winapi.CreateFile(
                    address, _winapi.GENERIC_READ | _winapi.GENERIC_WRITE,
                    0, _winapi.NULL, _winapi.OPEN_EXISTING,
                    _winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL
                    )
            except OSError as e:
                if e.winerror not in (_winapi.ERROR_SEM_TIMEOUT,
                                      _winapi.ERROR_PIPE_BUSY) or _check_timeout(t):
                    raise
            else:
                break
        else:
            raise

_winapi.SetNamedPipeHandleState(
            h, _winapi.PIPE_READMODE_MESSAGE, None, None
            )
        return PipeConnection(h)

#
# Authentication stuff
#

MESSAGE_LENGTH = 20

CHALLENGE = b'#CHALLENGE#'
WELCOME = b'#WELCOME#'
FAILURE = b'#FAILURE#'

def deliver_challenge(connection, authkey):
    import hmac
    if not isinstance(authkey, bytes):
        raise ValueError(
            "Authkey must be bytes, not {0!s}".format(type(authkey)))
    message = os.urandom(MESSAGE_LENGTH)
    connection.send_bytes(CHALLENGE + message)
    digest = hmac.new(authkey, message, 'md5').digest()
    response = connection.recv_bytes(256)        # reject large message
    if response == digest:
        connection.send_bytes(WELCOME)
    else:
        connection.send_bytes(FAILURE)
        raise AuthenticationError('digest received was wrong')

def answer_challenge(connection, authkey):
    import hmac
    if not isinstance(authkey, bytes):
        raise ValueError(
            "Authkey must be bytes, not {0!s}".format(type(authkey)))
    message = connection.recv_bytes(256)         # reject large message
    assert message[:len(CHALLENGE)] == CHALLENGE, 'message = %r' % message
    message = message[len(CHALLENGE):]
    digest = hmac.new(authkey, message, 'md5').digest()
    connection.send_bytes(digest)
    response = connection.recv_bytes(256)        # reject large message
    if response != WELCOME:
        raise AuthenticationError('digest sent was rejected')

#
# Support for using xmlrpclib for serialization
#

class ConnectionWrapper(object):
    def __init__(self, conn, dumps, loads):
        self._conn = conn
        self._dumps = dumps
        self._loads = loads
        for attr in ('fileno', 'close', 'poll', 'recv_bytes', 'send_bytes'):
            obj = getattr(conn, attr)
            setattr(self, attr, obj)
    def send(self, obj):
        s = self._dumps(obj)
        self._conn.send_bytes(s)
    def recv(self):
        s = self._conn.recv_bytes()
        return self._loads(s)

def _xml_dumps(obj):
    return xmlrpclib.dumps((obj,), None, None, None, 1).encode('utf-8')

def _xml_loads(s):
    (obj,), method = xmlrpclib.loads(s.decode('utf-8'))
    return obj

class XmlListener(Listener):
    def accept(self):
        global xmlrpclib
        import xmlrpc.client as xmlrpclib
        obj = Listener.accept(self)
        return ConnectionWrapper(obj, _xml_dumps, _xml_loads)

def XmlClient(*args, **kwds):
    global xmlrpclib
    import xmlrpc.client as xmlrpclib
    return ConnectionWrapper(Client(*args, **kwds), _xml_dumps, _xml_loads)

#
# Wait
#

if sys.platform == 'win32':

def _exhaustive_wait(handles, timeout):
        # Return ALL handles which are currently signalled.  (Only
        # returning the first signalled might create starvation issues.)
        L = list(handles)
        ready = []
        while L:
            res = _winapi.WaitForMultipleObjects(L, False, timeout)
            if res == WAIT_TIMEOUT:
                break
            elif WAIT_OBJECT_0 <= res < WAIT_OBJECT_0 + len(L):
                res -= WAIT_OBJECT_0
            elif WAIT_ABANDONED_0 <= res < WAIT_ABANDONED_0 + len(L):
                res -= WAIT_ABANDONED_0
            else:
                raise RuntimeError('Should not get here')
            ready.append(L[res])
            L = L[res+1:]
            timeout = 0
        return ready

_ready_errors = {_winapi.ERROR_BROKEN_PIPE, _winapi.ERROR_NETNAME_DELETED}

def wait(object_list, timeout=None):
        '''
        Wait till an object in object_list is ready/readable.

Returns list of those objects in object_list which are ready/readable.
        '''
        if timeout is None:
            timeout = INFINITE
        elif timeout < 0:
            timeout = 0
        else:
            timeout = int(timeout * 1000 + 0.5)

object_list = list(object_list)
        waithandle_to_obj = {}
        ov_list = []
        ready_objects = set()
        ready_handles = set()

try:
            for o in object_list:
                try:
                    fileno = getattr(o, 'fileno')
                except AttributeError:
                    waithandle_to_obj[o.__index__()] = o
                else:
                    # start an overlapped read of length zero
                    try:
                        ov, err = _winapi.ReadFile(fileno(), 0, True)
                    except OSError as e:
                        ov, err = None, e.winerror
                        if err not in _ready_errors:
                            raise
                    if err == _winapi.ERROR_IO_PENDING:
                        ov_list.append(ov)
                        waithandle_to_obj[ov.event] = o
                    else:
                        # If o.fileno() is an overlapped pipe handle and
                        # err == 0 then there is a zero length message
                        # in the pipe, but it HAS NOT been consumed...
                        if ov and sys.getwindowsversion()[:2] >= (6, 2):
                            # ... except on Windows 8 and later, where
                            # the message HAS been consumed.
                            try:
                                _, err = ov.GetOverlappedResult(False)
                            except OSError as e:
                                err = e.winerror
                            if not err and hasattr(o, '_got_empty_message'):
                                o._got_empty_message = True
                        ready_objects.add(o)
                        timeout = 0

ready_handles = _exhaustive_wait(waithandle_to_obj.keys(), timeout)
        finally:
            # request that overlapped reads stop
            for ov in ov_list:
                ov.cancel()

# wait for all overlapped reads to stop
            for ov in ov_list:
                try:
                    _, err = ov.GetOverlappedResult(True)
                except OSError as e:
                    err = e.winerror
                    if err not in _ready_errors:
                        raise
                if err != _winapi.ERROR_OPERATION_ABORTED:
                    o = waithandle_to_obj[ov.event]
                    ready_objects.add(o)
                    if err == 0:
                        # If o.fileno() is an overlapped pipe handle then
                        # a zero length message HAS been consumed.
                        if hasattr(o, '_got_empty_message'):
                            o._got_empty_message = True

ready_objects.update(waithandle_to_obj[h] for h in ready_handles)
        return [o for o in object_list if o in ready_objects]

else:

import selectors

# poll/select have the advantage of not requiring any extra file
    # descriptor, contrarily to epoll/kqueue (also, they require a single
    # syscall).
    if hasattr(selectors, 'PollSelector'):
        _WaitSelector = selectors.PollSelector
    else:
        _WaitSelector = selectors.SelectSelector

def wait(object_list, timeout=None):
        '''
        Wait till an object in object_list is ready/readable.

Returns list of those objects in object_list which are ready/readable.
        '''
        with _WaitSelector() as selector:
            for obj in object_list:
                selector.register(obj, selectors.EVENT_READ)

if timeout is not None:
                deadline = time.monotonic() + timeout

while True:
                ready = selector.select(timeout)
                if ready:
                    return [key.fileobj for (key, events) in ready]
                else:
                    if timeout is not None:
                        timeout = deadline - time.monotonic()
                        if timeout < 0:
                            return ready

#
# Make connection and socket objects sharable if possible
#

if sys.platform == 'win32':
    def reduce_connection(conn):
        handle = conn.fileno()
        with socket.fromfd(handle, socket.AF_INET, socket.SOCK_STREAM) as s:
            from . import resource_sharer
            ds = resource_sharer.DupSocket(s)
            return rebuild_connection, (ds, conn.readable, conn.writable)
    def rebuild_connection(ds, readable, writable):
        sock = ds.detach()
        return Connection(sock.detach(), readable, writable)
    reduction.register(Connection, reduce_connection)

def reduce_pipe_connection(conn):
        access = ((_winapi.FILE_GENERIC_READ if conn.readable else 0) |
                  (_winapi.FILE_GENERIC_WRITE if conn.writable else 0))
        dh = reduction.DupHandle(conn.fileno(), access)
        return rebuild_pipe_connection, (dh, conn.readable, conn.writable)
    def rebuild_pipe_connection(dh, readable, writable):
        handle = dh.detach()
        return PipeConnection(handle, readable, writable)
    reduction.register(PipeConnection, reduce_pipe_connection)

else:
    def reduce_connection(conn):
        df = reduction.DupFd(conn.fileno())
        return rebuild_connection, (df, conn.readable, conn.writable)
    def rebuild_connection(df, readable, writable):
        fd = df.detach()
        return Connection(fd, readable, writable)
    reduction.register(Connection, reduce_connection)

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