text: """Base implementation of event loop.
  
  The event loop can be broken up into a multiplexer (the part
  responsible for notifying us of I/O events) and the event loop proper,
  which wraps a multiplexer with functionality for scheduling callbacks,
  immediately or at a given time in the future.
  
  Whenever a public API takes a callback, subsequent positional
  arguments will be passed to the callback if/when it is called.  This
  avoids the proliferation of trivial lambdas implementing closures.
  Keyword arguments for the callback are not supported; this is a
  conscious design decision, leaving the door open for keyword arguments
  to modify the meaning of the API call itself.
  """
  
  import collections
  import collections.abc
  import concurrent.futures
  import functools
  import heapq
  import itertools
  import os
  import socket
  import stat
  import subprocess
  import threading
  import time
  import traceback
  import sys
  import warnings
  import weakref
  
  try:
      import ssl
  except ImportError:  # pragma: no cover
      ssl = None
  
  from . import constants
  from . import coroutines
  from . import events
  from . import exceptions
  from . import futures
  from . import protocols
  from . import sslproto
  from . import staggered
  from . import tasks
  from . import transports
  from .log import logger
  
  
  __all__ = 'BaseEventLoop',
  
  
  # Minimum number of _scheduled timer handles before cleanup of
  # cancelled handles is performed.
  _MIN_SCHEDULED_TIMER_HANDLES = 100
  
  # Minimum fraction of _scheduled timer handles that are cancelled
  # before cleanup of cancelled handles is performed.
  _MIN_CANCELLED_TIMER_HANDLES_FRACTION = 0.5
  
  # Exceptions which must not call the exception handler in fatal error
  # methods (_fatal_error())
  _FATAL_ERROR_IGNORE = (BrokenPipeError,
                         ConnectionResetError, ConnectionAbortedError)
  
  if ssl is not None:
      _FATAL_ERROR_IGNORE = _FATAL_ERROR_IGNORE + (ssl.SSLCertVerificationError,)
  
  _HAS_IPv6 = hasattr(socket, 'AF_INET6')
  
  # Maximum timeout passed to select to avoid OS limitations
  MAXIMUM_SELECT_TIMEOUT = 24 * 3600
  
  
  def _format_handle(handle):
      cb = handle._callback
      if isinstance(getattr(cb, '__self__', None), tasks.Task):
          # format the task
          return repr(cb.__self__)
      else:
          return str(handle)
  
  
  def _format_pipe(fd):
      if fd == subprocess.PIPE:
          return '<pipe>'
      elif fd == subprocess.STDOUT:
          return '<stdout>'
      else:
          return repr(fd)
  
  
  def _set_reuseport(sock):
      if not hasattr(socket, 'SO_REUSEPORT'):
          raise ValueError('reuse_port not supported by socket module')
      else:
          try:
              sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
          except OSError:
              raise ValueError('reuse_port not supported by socket module, '
                               'SO_REUSEPORT defined but not implemented.')
  
  
  def _ipaddr_info(host, port, family, type, proto):
      # Try to skip getaddrinfo if "host" is already an IP. Users might have
      # handled name resolution in their own code and pass in resolved IPs.
      if not hasattr(socket, 'inet_pton'):
          return
  
      if proto not in {0, socket.IPPROTO_TCP, socket.IPPROTO_UDP} or \
              host is None:
          return None
  
      if type == socket.SOCK_STREAM:
          proto = socket.IPPROTO_TCP
      elif type == socket.SOCK_DGRAM:
          proto = socket.IPPROTO_UDP
      else:
          return None
  
      if port is None:
          port = 0
      elif isinstance(port, bytes) and port == b'':
          port = 0
      elif isinstance(port, str) and port == '':
          port = 0
      else:
          # If port's a service name like "http", don't skip getaddrinfo.
          try:
              port = int(port)
          except (TypeError, ValueError):
              return None
  
      if family == socket.AF_UNSPEC:
          afs = [socket.AF_INET]
          if _HAS_IPv6:
              afs.append(socket.AF_INET6)
      else:
          afs = [family]
  
      if isinstance(host, bytes):
          host = host.decode('idna')
      if '%' in host:
          # Linux's inet_pton doesn't accept an IPv6 zone index after host,
          # like '::1%lo0'.
          return None
  
      for af in afs:
          try:
              socket.inet_pton(af, host)
              # The host has already been resolved.
              if _HAS_IPv6 and af == socket.AF_INET6:
                  return af, type, proto, '', (host, port, 0, 0)
              else:
                  return af, type, proto, '', (host, port)
          except OSError:
              pass
  
      # "host" is not an IP address.
      return None
  
  
  def _interleave_addrinfos(addrinfos, first_address_family_count=1):
      """Interleave list of addrinfo tuples by family."""
      # Group addresses by family
      addrinfos_by_family = collections.OrderedDict()
      for addr in addrinfos:
          family = addr[0]
          if family not in addrinfos_by_family:
              addrinfos_by_family[family] = []
          addrinfos_by_family[family].append(addr)
      addrinfos_lists = list(addrinfos_by_family.values())
  
      reordered = []
      if first_address_family_count > 1:
          reordered.extend(addrinfos_lists[0][:first_address_family_count - 1])
          del addrinfos_lists[0][:first_address_family_count - 1]
      reordered.extend(
          a for a in itertools.chain.from_iterable(
              itertools.zip_longest(*addrinfos_lists)
          ) if a is not None)
      return reordered
  
  
  def _run_until_complete_cb(fut):
      if not fut.cancelled():
          exc = fut.exception()
          if isinstance(exc, BaseException) and not isinstance(exc, Exception):
              # Issue #22429: run_forever() already finished, no need to
              # stop it.
              return
      futures._get_loop(fut).stop()
  
  
  if hasattr(socket, 'TCP_NODELAY'):
      def _set_nodelay(sock):
          if (sock.family in {socket.AF_INET, socket.AF_INET6} and
                  sock.type == socket.SOCK_STREAM and
                  sock.proto == socket.IPPROTO_TCP):
              sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
  else:
      def _set_nodelay(sock):
          pass
  
  
  class _SendfileFallbackProtocol(protocols.Protocol):
      def __init__(self, transp):
          if not isinstance(transp, transports._FlowControlMixin):
              raise TypeError("transport should be _FlowControlMixin instance")
          self._transport = transp
          self._proto = transp.get_protocol()
          self._should_resume_reading = transp.is_reading()
          self._should_resume_writing = transp._protocol_paused
          transp.pause_reading()
          transp.set_protocol(self)
          if self._should_resume_writing:
              self._write_ready_fut = self._transport._loop.create_future()
          else:
              self._write_ready_fut = None
  
      async def drain(self):
          if self._transport.is_closing():
              raise ConnectionError("Connection closed by peer")
          fut = self._write_ready_fut
          if fut is None:
              return
          await fut
  
      def connection_made(self, transport):
          raise RuntimeError("Invalid state: "
                             "connection should have been established already.")
  
      def connection_lost(self, exc):
          if self._write_ready_fut is not None:
              # Never happens if peer disconnects after sending the whole content
              # Thus disconnection is always an exception from user perspective
              if exc is None:
                  self._write_ready_fut.set_exception(
                      ConnectionError("Connection is closed by peer"))
              else:
                  self._write_ready_fut.set_exception(exc)
          self._proto.connection_lost(exc)
  
      def pause_writing(self):
          if self._write_ready_fut is not None:
              return
          self._write_ready_fut = self._transport._loop.create_future()
  
      def resume_writing(self):
          if self._write_ready_fut is None:
              return
          self._write_ready_fut.set_result(False)
          self._write_ready_fut = None
  
      def data_received(self, data):
          raise RuntimeError("Invalid state: reading should be paused")
  
      def eof_received(self):
          raise RuntimeError("Invalid state: reading should be paused")
  
      async def restore(self):
          self._transport.set_protocol(self._proto)
          if self._should_resume_reading:
              self._transport.resume_reading()
          if self._write_ready_fut is not None:
              # Cancel the future.
              # Basically it has no effect because protocol is switched back,
              # no code should wait for it anymore.
              self._write_ready_fut.cancel()
          if self._should_resume_writing:
              self._proto.resume_writing()
  
  
  class Server(events.AbstractServer):
  
      def __init__(self, loop, sockets, protocol_factory, ssl_context, backlog,
                   ssl_handshake_timeout):
          self._loop = loop
          self._sockets = sockets
          self._active_count = 0
          self._waiters = []
          self._protocol_factory = protocol_factory
          self._backlog = backlog
          self._ssl_context = ssl_context
          self._ssl_handshake_timeout = ssl_handshake_timeout
          self._serving = False
          self._serving_forever_fut = None
  
      def __repr__(self):
          return f'<{self.__class__.__name__} sockets={self.sockets!r}>'
  
      def _attach(self):
          assert self._sockets is not None
          self._active_count += 1
  
      def _detach(self):
          assert self._active_count > 0
          self._active_count -= 1
          if self._active_count == 0 and self._sockets is None:
              self._wakeup()
  
      def _wakeup(self):
          waiters = self._waiters
          self._waiters = None
          for waiter in waiters:
              if not waiter.done():
                  waiter.set_result(waiter)
  
      def _start_serving(self):
          if self._serving:
              return
          self._serving = True
          for sock in self._sockets:
              sock.listen(self._backlog)
              self._loop._start_serving(
                  self._protocol_factory, sock, self._ssl_context,
                  self, self._backlog, self._ssl_handshake_timeout)
  
      def get_loop(self):
          return self._loop
  
      def is_serving(self):
          return self._serving
  
      @property
      def sockets(self):
          if self._sockets is None:
              return []
          return list(self._sockets)
  
      def close(self):
          sockets = self._sockets
          if sockets is None:
              return
          self._sockets = None
  
          for sock in sockets:
              self._loop._stop_serving(sock)
  
          self._serving = False
  
          if (self._serving_forever_fut is not None and
                  not self._serving_forever_fut.done()):
              self._serving_forever_fut.cancel()
              self._serving_forever_fut = None
  
          if self._active_count == 0:
              self._wakeup()
  
      async def start_serving(self):
          self._start_serving()
          # Skip one loop iteration so that all 'loop.add_reader'
          # go through.
          await tasks.sleep(0, loop=self._loop)
  
      async def serve_forever(self):
          if self._serving_forever_fut is not None:
              raise RuntimeError(
                  f'server {self!r} is already being awaited on serve_forever()')
          if self._sockets is None:
              raise RuntimeError(f'server {self!r} is closed')
  
          self._start_serving()
          self._serving_forever_fut = self._loop.create_future()
  
          try:
              await self._serving_forever_fut
          except exceptions.CancelledError:
              try:
                  self.close()
                  await self.wait_closed()
              finally:
                  raise
          finally:
              self._serving_forever_fut = None
  
      async def wait_closed(self):
          if self._sockets is None or self._waiters is None:
              return
          waiter = self._loop.create_future()
          self._waiters.append(waiter)
          await waiter
  
  
  class BaseEventLoop(events.AbstractEventLoop):
  
      def __init__(self):
          self._timer_cancelled_count = 0
          self._closed = False
          self._stopping = False
          self._ready = collections.deque()
          self._scheduled = []
          self._default_executor = None
          self._internal_fds = 0
          # Identifier of the thread running the event loop, or None if the
          # event loop is not running
          self._thread_id = None
          self._clock_resolution = time.get_clock_info('monotonic').resolution
          self._exception_handler = None
          self.set_debug(coroutines._is_debug_mode())
          # In debug mode, if the execution of a callback or a step of a task
          # exceed this duration in seconds, the slow callback/task is logged.
          self.slow_callback_duration = 0.1
          self._current_handle = None
          self._task_factory = None
          self._coroutine_origin_tracking_enabled = False
          self._coroutine_origin_tracking_saved_depth = None
  
          # A weak set of all asynchronous generators that are
          # being iterated by the loop.
          self._asyncgens = weakref.WeakSet()
          # Set to True when `loop.shutdown_asyncgens` is called.
          self._asyncgens_shutdown_called = False
  
      def __repr__(self):
          return (
              f'<{self.__class__.__name__} running={self.is_running()} '
              f'closed={self.is_closed()} debug={self.get_debug()}>'
          )
  
      def create_future(self):
          """Create a Future object attached to the loop."""
          return futures.Future(loop=self)
  
      def create_task(self, coro, *, name=None):
          """Schedule a coroutine object.
  
          Return a task object.
          """
          self._check_closed()
          if self._task_factory is None:
              task = tasks.Task(coro, loop=self, name=name)
              if task._source_traceback:
                  del task._source_traceback[-1]
          else:
              task = self._task_factory(self, coro)
              tasks._set_task_name(task, name)
  
          return task
  
      def set_task_factory(self, factory):
          """Set a task factory that will be used by loop.create_task().
  
          If factory is None the default task factory will be set.
  
          If factory is a callable, it should have a signature matching
          '(loop, coro)', where 'loop' will be a reference to the active
          event loop, 'coro' will be a coroutine object.  The callable
          must return a Future.
          """
          if factory is not None and not callable(factory):
              raise TypeError('task factory must be a callable or None')
          self._task_factory = factory
  
      def get_task_factory(self):
          """Return a task factory, or None if the default one is in use."""
          return self._task_factory
  
      def _make_socket_transport(self, sock, protocol, waiter=None, *,
                                 extra=None, server=None):
          """Create socket transport."""
          raise NotImplementedError
  
      def _make_ssl_transport(
              self, rawsock, protocol, sslcontext, waiter=None,
              *, server_side=False, server_hostname=None,
              extra=None, server=None,
              ssl_handshake_timeout=None,
              call_connection_made=True):
          """Create SSL transport."""
          raise NotImplementedError
  
      def _make_datagram_transport(self, sock, protocol,
                                   address=None, waiter=None, extra=None):
          """Create datagram transport."""
          raise NotImplementedError
  
      def _make_read_pipe_transport(self, pipe, protocol, waiter=None,
                                    extra=None):
          """Create read pipe transport."""
          raise NotImplementedError
  
      def _make_write_pipe_transport(self, pipe, protocol, waiter=None,
                                     extra=None):
          """Create write pipe transport."""
          raise NotImplementedError
  
      async def _make_subprocess_transport(self, protocol, args, shell,
                                           stdin, stdout, stderr, bufsize,
                                           extra=None, **kwargs):
          """Create subprocess transport."""
          raise NotImplementedError
  
      def _write_to_self(self):
          """Write a byte to self-pipe, to wake up the event loop.
  
          This may be called from a different thread.
  
          The subclass is responsible for implementing the self-pipe.
          """
          raise NotImplementedError
  
      def _process_events(self, event_list):
          """Process selector events."""
          raise NotImplementedError
  
      def _check_closed(self):
          if self._closed:
              raise RuntimeError('Event loop is closed')
  
      def _asyncgen_finalizer_hook(self, agen):
          self._asyncgens.discard(agen)
          if not self.is_closed():
              self.call_soon_threadsafe(self.create_task, agen.aclose())
  
      def _asyncgen_firstiter_hook(self, agen):
          if self._asyncgens_shutdown_called:
              warnings.warn(
                  f"asynchronous generator {agen!r} was scheduled after "
                  f"loop.shutdown_asyncgens() call",
                  ResourceWarning, source=self)
  
          self._asyncgens.add(agen)
  
      async def shutdown_asyncgens(self):
          """Shutdown all active asynchronous generators."""
          self._asyncgens_shutdown_called = True
  
          if not len(self._asyncgens):
              # If Python version is <3.6 or we don't have any asynchronous
              # generators alive.
              return
  
          closing_agens = list(self._asyncgens)
          self._asyncgens.clear()
  
          results = await tasks.gather(
              *[ag.aclose() for ag in closing_agens],
              return_exceptions=True,
              loop=self)
  
          for result, agen in zip(results, closing_agens):
              if isinstance(result, Exception):
                  self.call_exception_handler({
                      'message': f'an error occurred during closing of '
                                 f'asynchronous generator {agen!r}',
                      'exception': result,
                      'asyncgen': agen
                  })
  
      def run_forever(self):
          """Run until stop() is called."""
          self._check_closed()
          if self.is_running():
              raise RuntimeError('This event loop is already running')
          if events._get_running_loop() is not None:
              raise RuntimeError(
                  'Cannot run the event loop while another loop is running')
          self._set_coroutine_origin_tracking(self._debug)
          self._thread_id = threading.get_ident()
  
          old_agen_hooks = sys.get_asyncgen_hooks()
          sys.set_asyncgen_hooks(firstiter=self._asyncgen_firstiter_hook,
                                 finalizer=self._asyncgen_finalizer_hook)
          try:
              events._set_running_loop(self)
              while True:
                  self._run_once()
                  if self._stopping:
                      break
          finally:
              self._stopping = False
              self._thread_id = None
              events._set_running_loop(None)
              self._set_coroutine_origin_tracking(False)
              sys.set_asyncgen_hooks(*old_agen_hooks)
  
      def run_until_complete(self, future):
          """Run until the Future is done.
  
          If the argument is a coroutine, it is wrapped in a Task.
  
          WARNING: It would be disastrous to call run_until_complete()
          with the same coroutine twice -- it would wrap it in two
          different Tasks and that can't be good.
  
          Return the Future's result, or raise its exception.
          """
          self._check_closed()
  
          new_task = not futures.isfuture(future)
          future = tasks.ensure_future(future, loop=self)
          if new_task:
              # An exception is raised if the future didn't complete, so there
              # is no need to log the "destroy pending task" message
              future._log_destroy_pending = False
  
          future.add_done_callback(_run_until_complete_cb)
          try:
              self.run_forever()
          except:
              if new_task and future.done() and not future.cancelled():
                  # The coroutine raised a BaseException. Consume the exception
                  # to not log a warning, the caller doesn't have access to the
                  # local task.
                  future.exception()
              raise
          finally:
              future.remove_done_callback(_run_until_complete_cb)
          if not future.done():
              raise RuntimeError('Event loop stopped before Future completed.')
  
          return future.result()
  
      def stop(self):
          """Stop running the event loop.
  
          Every callback already scheduled will still run.  This simply informs
          run_forever to stop looping after a complete iteration.
          """
          self._stopping = True
  
      def close(self):
          """Close the event loop.
  
          This clears the queues and shuts down the executor,
          but does not wait for the executor to finish.
  
          The event loop must not be running.
          """
          if self.is_running():
              raise RuntimeError("Cannot close a running event loop")
          if self._closed:
              return
          if self._debug:
              logger.debug("Close %r", self)
          self._closed = True
          self._ready.clear()
          self._scheduled.clear()
          executor = self._default_executor
          if executor is not None:
              self._default_executor = None
              executor.shutdown(wait=False)
  
      def is_closed(self):
          """Returns True if the event loop was closed."""
          return self._closed
  
      def __del__(self, _warn=warnings.warn):
          if not self.is_closed():
              _warn(f"unclosed event loop {self!r}", ResourceWarning, source=self)
              if not self.is_running():
                  self.close()
  
      def is_running(self):
          """Returns True if the event loop is running."""
          return (self._thread_id is not None)
  
      def time(self):
          """Return the time according to the event loop's clock.
  
          This is a float expressed in seconds since an epoch, but the
          epoch, precision, accuracy and drift are unspecified and may
          differ per event loop.
          """
          return time.monotonic()
  
      def call_later(self, delay, callback, *args, context=None):
          """Arrange for a callback to be called at a given time.
  
          Return a Handle: an opaque object with a cancel() method that
          can be used to cancel the call.
  
          The delay can be an int or float, expressed in seconds.  It is
          always relative to the current time.
  
          Each callback will be called exactly once.  If two callbacks
          are scheduled for exactly the same time, it undefined which
          will be called first.
  
          Any positional arguments after the callback will be passed to
          the callback when it is called.
          """
          timer = self.call_at(self.time() + delay, callback, *args,
                               context=context)
          if timer._source_traceback:
              del timer._source_traceback[-1]
          return timer
  
      def call_at(self, when, callback, *args, context=None):
          """Like call_later(), but uses an absolute time.
  
          Absolute time corresponds to the event loop's time() method.
          """
          self._check_closed()
          if self._debug:
              self._check_thread()
              self._check_callback(callback, 'call_at')
          timer = events.TimerHandle(when, callback, args, self, context)
          if timer._source_traceback:
              del timer._source_traceback[-1]
          heapq.heappush(self._scheduled, timer)
          timer._scheduled = True
          return timer
  
      def call_soon(self, callback, *args, context=None):
          """Arrange for a callback to be called as soon as possible.
  
          This operates as a FIFO queue: callbacks are called in the
          order in which they are registered.  Each callback will be
          called exactly once.
  
          Any positional arguments after the callback will be passed to
          the callback when it is called.
          """
          self._check_closed()
          if self._debug:
              self._check_thread()
              self._check_callback(callback, 'call_soon')
          handle = self._call_soon(callback, args, context)
          if handle._source_traceback:
              del handle._source_traceback[-1]
          return handle
  
      def _check_callback(self, callback, method):
          if (coroutines.iscoroutine(callback) or
                  coroutines.iscoroutinefunction(callback)):
              raise TypeError(
                  f"coroutines cannot be used with {method}()")
          if not callable(callback):
              raise TypeError(
                  f'a callable object was expected by {method}(), '
                  f'got {callback!r}')
  
      def _call_soon(self, callback, args, context):
          handle = events.Handle(callback, args, self, context)
          if handle._source_traceback:
              del handle._source_traceback[-1]
          self._ready.append(handle)
          return handle
  
      def _check_thread(self):
          """Check that the current thread is the thread running the event loop.
  
          Non-thread-safe methods of this class make this assumption and will
          likely behave incorrectly when the assumption is violated.
  
          Should only be called when (self._debug == True).  The caller is
          responsible for checking this condition for performance reasons.
          """
          if self._thread_id is None:
              return
          thread_id = threading.get_ident()
          if thread_id != self._thread_id:
              raise RuntimeError(
                  "Non-thread-safe operation invoked on an event loop other "
                  "than the current one")
  
      def call_soon_threadsafe(self, callback, *args, context=None):
          """Like call_soon(), but thread-safe."""
          self._check_closed()
          if self._debug:
              self._check_callback(callback, 'call_soon_threadsafe')
          handle = self._call_soon(callback, args, context)
          if handle._source_traceback:
              del handle._source_traceback[-1]
          self._write_to_self()
          return handle
  
      def run_in_executor(self, executor, func, *args):
          self._check_closed()
          if self._debug:
              self._check_callback(func, 'run_in_executor')
          if executor is None:
              executor = self._default_executor
              if executor is None:
                  executor = concurrent.futures.ThreadPoolExecutor()
                  self._default_executor = executor
          return futures.wrap_future(
              executor.submit(func, *args), loop=self)
  
      def set_default_executor(self, executor):
          if not isinstance(executor, concurrent.futures.ThreadPoolExecutor):
              warnings.warn(
                  'Using the default executor that is not an instance of '
                  'ThreadPoolExecutor is deprecated and will be prohibited '
                  'in Python 3.9',
                  DeprecationWarning, 2)
          self._default_executor = executor
  
      def _getaddrinfo_debug(self, host, port, family, type, proto, flags):
          msg = [f"{host}:{port!r}"]
          if family:
              msg.append(f'family={family!r}')
          if type:
              msg.append(f'type={type!r}')
          if proto:
              msg.append(f'proto={proto!r}')
          if flags:
              msg.append(f'flags={flags!r}')
          msg = ', '.join(msg)
          logger.debug('Get address info %s', msg)
  
          t0 = self.time()
          addrinfo = socket.getaddrinfo(host, port, family, type, proto, flags)
          dt = self.time() - t0
  
          msg = f'Getting address info {msg} took {dt * 1e3:.3f}ms: {addrinfo!r}'
          if dt >= self.slow_callback_duration:
              logger.info(msg)
          else:
              logger.debug(msg)
          return addrinfo
  
      async def getaddrinfo(self, host, port, *,
                            family=0, type=0, proto=0, flags=0):
          if self._debug:
              getaddr_func = self._getaddrinfo_debug
          else:
              getaddr_func = socket.getaddrinfo
  
          return await self.run_in_executor(
              None, getaddr_func, host, port, family, type, proto, flags)
  
      async def getnameinfo(self, sockaddr, flags=0):
          return await self.run_in_executor(
              None, socket.getnameinfo, sockaddr, flags)
  
      async def sock_sendfile(self, sock, file, offset=0, count=None,
                              *, fallback=True):
          if self._debug and sock.gettimeout() != 0:
              raise ValueError("the socket must be non-blocking")
          self._check_sendfile_params(sock, file, offset, count)
          try:
              return await self._sock_sendfile_native(sock, file,
                                                      offset, count)
          except exceptions.SendfileNotAvailableError as exc:
              if not fallback:
                  raise
          return await self._sock_sendfile_fallback(sock, file,
                                                    offset, count)
  
      async def _sock_sendfile_native(self, sock, file, offset, count):
          # NB: sendfile syscall is not supported for SSL sockets and
          # non-mmap files even if sendfile is supported by OS
          raise exceptions.SendfileNotAvailableError(
              f"syscall sendfile is not available for socket {sock!r} "
              "and file {file!r} combination")
  
      async def _sock_sendfile_fallback(self, sock, file, offset, count):
          if offset:
              file.seek(offset)
          blocksize = (
              min(count, constants.SENDFILE_FALLBACK_READBUFFER_SIZE)
              if count else constants.SENDFILE_FALLBACK_READBUFFER_SIZE
          )
          buf = bytearray(blocksize)
          total_sent = 0
          try:
              while True:
                  if count:
                      blocksize = min(count - total_sent, blocksize)
                      if blocksize <= 0:
                          break
                  view = memoryview(buf)[:blocksize]
                  read = await self.run_in_executor(None, file.readinto, view)
                  if not read:
                      break  # EOF
                  await self.sock_sendall(sock, view)
                  total_sent += read
              return total_sent
          finally:
              if total_sent > 0 and hasattr(file, 'seek'):
                  file.seek(offset + total_sent)
  
      def _check_sendfile_params(self, sock, file, offset, count):
          if 'b' not in getattr(file, 'mode', 'b'):
              raise ValueError("file should be opened in binary mode")
          if not sock.type == socket.SOCK_STREAM:
              raise ValueError("only SOCK_STREAM type sockets are supported")
          if count is not None:
              if not isinstance(count, int):
                  raise TypeError(
                      "count must be a positive integer (got {!r})".format(count))
              if count <= 0:
                  raise ValueError(
                      "count must be a positive integer (got {!r})".format(count))
          if not isinstance(offset, int):
              raise TypeError(
                  "offset must be a non-negative integer (got {!r})".format(
                      offset))
          if offset < 0:
              raise ValueError(
                  "offset must be a non-negative integer (got {!r})".format(
                      offset))
  
      async def _connect_sock(self, exceptions, addr_info, local_addr_infos=None):
          """Create, bind and connect one socket."""
          my_exceptions = []
          exceptions.append(my_exceptions)
          family, type_, proto, _, address = addr_info
          sock = None
          try:
              sock = socket.socket(family=family, type=type_, proto=proto)
              sock.setblocking(False)
              if local_addr_infos is not None:
                  for _, _, _, _, laddr in local_addr_infos:
                      try:
                          sock.bind(laddr)
                          break
                      except OSError as exc:
                          msg = (
                              f'error while attempting to bind on '
                              f'address {laddr!r}: '
                              f'{exc.strerror.lower()}'
                          )
                          exc = OSError(exc.errno, msg)
                          my_exceptions.append(exc)
                  else:  # all bind attempts failed
                      raise my_exceptions.pop()
              await self.sock_connect(sock, address)
              return sock
          except OSError as exc:
              my_exceptions.append(exc)
              if sock is not None:
                  sock.close()
              raise
          except:
              if sock is not None:
                  sock.close()
              raise
  
      async def create_connection(
              self, protocol_factory, host=None, port=None,
              *, ssl=None, family=0,
              proto=0, flags=0, sock=None,
              local_addr=None, server_hostname=None,
              ssl_handshake_timeout=None,
              happy_eyeballs_delay=None, interleave=None):
          """Connect to a TCP server.
  
          Create a streaming transport connection to a given Internet host and
          port: socket family AF_INET or socket.AF_INET6 depending on host (or
          family if specified), socket type SOCK_STREAM. protocol_factory must be
          a callable returning a protocol instance.
  
          This method is a coroutine which will try to establish the connection
          in the background.  When successful, the coroutine returns a
          (transport, protocol) pair.
          """
          if server_hostname is not None and not ssl:
              raise ValueError('server_hostname is only meaningful with ssl')
  
          if server_hostname is None and ssl:
              # Use host as default for server_hostname.  It is an error
              # if host is empty or not set, e.g. when an
              # already-connected socket was passed or when only a port
              # is given.  To avoid this error, you can pass
              # server_hostname='' -- this will bypass the hostname
              # check.  (This also means that if host is a numeric
              # IP/IPv6 address, we will attempt to verify that exact
              # address; this will probably fail, but it is possible to
              # create a certificate for a specific IP address, so we
              # don't judge it here.)
              if not host:
                  raise ValueError('You must set server_hostname '
                                   'when using ssl without a host')
              server_hostname = host
  
          if ssl_handshake_timeout is not None and not ssl:
              raise ValueError(
                  'ssl_handshake_timeout is only meaningful with ssl')
  
          if happy_eyeballs_delay is not None and interleave is None:
              # If using happy eyeballs, default to interleave addresses by family
              interleave = 1
  
          if host is not None or port is not None:
              if sock is not None:
                  raise ValueError(
                      'host/port and sock can not be specified at the same time')
  
              infos = await self._ensure_resolved(
                  (host, port), family=family,
                  type=socket.SOCK_STREAM, proto=proto, flags=flags, loop=self)
              if not infos:
                  raise OSError('getaddrinfo() returned empty list')
  
              if local_addr is not None:
                  laddr_infos = await self._ensure_resolved(
                      local_addr, family=family,
                      type=socket.SOCK_STREAM, proto=proto,
                      flags=flags, loop=self)
                  if not laddr_infos:
                      raise OSError('getaddrinfo() returned empty list')
              else:
                  laddr_infos = None
  
              if interleave:
                  infos = _interleave_addrinfos(infos, interleave)
  
              exceptions = []
              if happy_eyeballs_delay is None:
                  # not using happy eyeballs
                  for addrinfo in infos:
                      try:
                          sock = await self._connect_sock(
                              exceptions, addrinfo, laddr_infos)
                          break
                      except OSError:
                          continue
              else:  # using happy eyeballs
                  sock, _, _ = await staggered.staggered_race(
                      (functools.partial(self._connect_sock,
                                         exceptions, addrinfo, laddr_infos)
                       for addrinfo in infos),
                      happy_eyeballs_delay, loop=self)
  
              if sock is None:
                  exceptions = [exc for sub in exceptions for exc in sub]
                  if len(exceptions) == 1:
                      raise exceptions[0]
                  else:
                      # If they all have the same str(), raise one.
                      model = str(exceptions[0])
                      if all(str(exc) == model for exc in exceptions):
                          raise exceptions[0]
                      # Raise a combined exception so the user can see all
                      # the various error messages.
                      raise OSError('Multiple exceptions: {}'.format(
                          ', '.join(str(exc) for exc in exceptions)))
  
          else:
              if sock is None:
                  raise ValueError(
                      'host and port was not specified and no sock specified')
              if sock.type != socket.SOCK_STREAM:
                  # We allow AF_INET, AF_INET6, AF_UNIX as long as they
                  # are SOCK_STREAM.
                  # We support passing AF_UNIX sockets even though we have
                  # a dedicated API for that: create_unix_connection.
                  # Disallowing AF_UNIX in this method, breaks backwards
                  # compatibility.
                  raise ValueError(
                      f'A Stream Socket was expected, got {sock!r}')
  
          transport, protocol = await self._create_connection_transport(
              sock, protocol_factory, ssl, server_hostname,
              ssl_handshake_timeout=ssl_handshake_timeout)
          if self._debug:
              # Get the socket from the transport because SSL transport closes
              # the old socket and creates a new SSL socket
              sock = transport.get_extra_info('socket')
              logger.debug("%r connected to %s:%r: (%r, %r)",
                           sock, host, port, transport, protocol)
          return transport, protocol
  
      async def _create_connection_transport(
              self, sock, protocol_factory, ssl,
              server_hostname, server_side=False,
              ssl_handshake_timeout=None):
  
          sock.setblocking(False)
  
          protocol = protocol_factory()
          waiter = self.create_future()
          if ssl:
              sslcontext = None if isinstance(ssl, bool) else ssl
              transport = self._make_ssl_transport(
                  sock, protocol, sslcontext, waiter,
                  server_side=server_side, server_hostname=server_hostname,
                  ssl_handshake_timeout=ssl_handshake_timeout)
          else:
              transport = self._make_socket_transport(sock, protocol, waiter)
  
          try:
              await waiter
          except:
              transport.close()
              raise
  
          return transport, protocol
  
      async def sendfile(self, transport, file, offset=0, count=None,
                         *, fallback=True):
          """Send a file to transport.
  
          Return the total number of bytes which were sent.
  
          The method uses high-performance os.sendfile if available.
  
          file must be a regular file object opened in binary mode.
  
          offset tells from where to start reading the file. If specified,
          count is the total number of bytes to transmit as opposed to
          sending the file until EOF is reached. File position is updated on
          return or also in case of error in which case file.tell()
          can be used to figure out the number of bytes
          which were sent.
  
          fallback set to True makes asyncio to manually read and send
          the file when the platform does not support the sendfile syscall
          (e.g. Windows or SSL socket on Unix).
  
          Raise SendfileNotAvailableError if the system does not support
          sendfile syscall and fallback is False.
          """
          if transport.is_closing():
              raise RuntimeError("Transport is closing")
          mode = getattr(transport, '_sendfile_compatible',
                         constants._SendfileMode.UNSUPPORTED)
          if mode is constants._SendfileMode.UNSUPPORTED:
              raise RuntimeError(
                  f"sendfile is not supported for transport {transport!r}")
          if mode is constants._SendfileMode.TRY_NATIVE:
              try:
                  return await self._sendfile_native(transport, file,
                                                     offset, count)
              except exceptions.SendfileNotAvailableError as exc:
                  if not fallback:
                      raise
  
          if not fallback:
              raise RuntimeError(
                  f"fallback is disabled and native sendfile is not "
                  f"supported for transport {transport!r}")
  
          return await self._sendfile_fallback(transport, file,
                                               offset, count)
  
      async def _sendfile_native(self, transp, file, offset, count):
          raise exceptions.SendfileNotAvailableError(
              "sendfile syscall is not supported")
  
      async def _sendfile_fallback(self, transp, file, offset, count):
          if offset:
              file.seek(offset)
          blocksize = min(count, 16384) if count else 16384
          buf = bytearray(blocksize)
          total_sent = 0
          proto = _SendfileFallbackProtocol(transp)
          try:
              while True:
                  if count:
                      blocksize = min(count - total_sent, blocksize)
                      if blocksize <= 0:
                          return total_sent
                  view = memoryview(buf)[:blocksize]
                  read = file.readinto(view)
                  if not read:
                      return total_sent  # EOF
                  await proto.drain()
                  transp.write(view)
                  total_sent += read
          finally:
              if total_sent > 0 and hasattr(file, 'seek'):
                  file.seek(offset + total_sent)
              await proto.restore()
  
      async def start_tls(self, transport, protocol, sslcontext, *,
                          server_side=False,
                          server_hostname=None,
                          ssl_handshake_timeout=None):
          """Upgrade transport to TLS.
  
          Return a new transport that *protocol* should start using
          immediately.
          """
          if ssl is None:
              raise RuntimeError('Python ssl module is not available')
  
          if not isinstance(sslcontext, ssl.SSLContext):
              raise TypeError(
                  f'sslcontext is expected to be an instance of ssl.SSLContext, '
                  f'got {sslcontext!r}')
  
          if not getattr(transport, '_start_tls_compatible', False):
              raise TypeError(
                  f'transport {transport!r} is not supported by start_tls()')
  
          waiter = self.create_future()
          ssl_protocol = sslproto.SSLProtocol(
              self, protocol, sslcontext, waiter,
              server_side, server_hostname,
              ssl_handshake_timeout=ssl_handshake_timeout,
              call_connection_made=False)
  
          # Pause early so that "ssl_protocol.data_received()" doesn't
          # have a chance to get called before "ssl_protocol.connection_made()".
          transport.pause_reading()
  
          transport.set_protocol(ssl_protocol)
          conmade_cb = self.call_soon(ssl_protocol.connection_made, transport)
          resume_cb = self.call_soon(transport.resume_reading)
  
          try:
              await waiter
          except Exception:
              transport.close()
              conmade_cb.cancel()
              resume_cb.cancel()
              raise
  
          return ssl_protocol._app_transport
  
      async def create_datagram_endpoint(self, protocol_factory,
                                         local_addr=None, remote_addr=None, *,
                                         family=0, proto=0, flags=0,
                                         reuse_address=None, reuse_port=None,
                                         allow_broadcast=None, sock=None):
          """Create datagram connection."""
          if sock is not None:
              if sock.type != socket.SOCK_DGRAM:
                  raise ValueError(
                      f'A UDP Socket was expected, got {sock!r}')
              if (local_addr or remote_addr or
                      family or proto or flags or
                      reuse_address or reuse_port or allow_broadcast):
                  # show the problematic kwargs in exception msg
                  opts = dict(local_addr=local_addr, remote_addr=remote_addr,
                              family=family, proto=proto, flags=flags,
                              reuse_address=reuse_address, reuse_port=reuse_port,
                              allow_broadcast=allow_broadcast)
                  problems = ', '.join(f'{k}={v}' for k, v in opts.items() if v)
                  raise ValueError(
                      f'socket modifier keyword arguments can not be used '
                      f'when sock is specified. ({problems})')
              sock.setblocking(False)
              r_addr = None
          else:
              if not (local_addr or remote_addr):
                  if family == 0:
                      raise ValueError('unexpected address family')
                  addr_pairs_info = (((family, proto), (None, None)),)
              elif hasattr(socket, 'AF_UNIX') and family == socket.AF_UNIX:
                  for addr in (local_addr, remote_addr):
                      if addr is not None and not isinstance(addr, str):
                          raise TypeError('string is expected')
  
                  if local_addr and local_addr[0] not in (0, '\x00'):
                      try:
                          if stat.S_ISSOCK(os.stat(local_addr).st_mode):
                              os.remove(local_addr)
                      except FileNotFoundError:
                          pass
                      except OSError as err:
                          # Directory may have permissions only to create socket.
                          logger.error('Unable to check or remove stale UNIX '
                                       'socket %r: %r',
                                       local_addr, err)
  
                  addr_pairs_info = (((family, proto),
                                      (local_addr, remote_addr)), )
              else:
                  # join address by (family, protocol)
                  addr_infos = {}  # Using order preserving dict
                  for idx, addr in ((0, local_addr), (1, remote_addr)):
                      if addr is not None:
                          assert isinstance(addr, tuple) and len(addr) == 2, (
                              '2-tuple is expected')
  
                          infos = await self._ensure_resolved(
                              addr, family=family, type=socket.SOCK_DGRAM,
                              proto=proto, flags=flags, loop=self)
                          if not infos:
                              raise OSError('getaddrinfo() returned empty list')
  
                          for fam, _, pro, _, address in infos:
                              key = (fam, pro)
                              if key not in addr_infos:
                                  addr_infos[key] = [None, None]
                              addr_infos[key][idx] = address
  
                  # each addr has to have info for each (family, proto) pair
                  addr_pairs_info = [
                      (key, addr_pair) for key, addr_pair in addr_infos.items()
                      if not ((local_addr and addr_pair[0] is None) or
                              (remote_addr and addr_pair[1] is None))]
  
                  if not addr_pairs_info:
                      raise ValueError('can not get address information')
  
              exceptions = []
  
              if reuse_address is None:
                  reuse_address = os.name == 'posix' and sys.platform != 'cygwin'
  
              for ((family, proto),
                   (local_address, remote_address)) in addr_pairs_info:
                  sock = None
                  r_addr = None
                  try:
                      sock = socket.socket(
                          family=family, type=socket.SOCK_DGRAM, proto=proto)
                      if reuse_address:
                          sock.setsockopt(
                              socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
                      if reuse_port:
                          _set_reuseport(sock)
                      if allow_broadcast:
                          sock.setsockopt(
                              socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
                      sock.setblocking(False)
  
                      if local_addr:
                          sock.bind(local_address)
                      if remote_addr:
                          if not allow_broadcast:
                              await self.sock_connect(sock, remote_address)
                          r_addr = remote_address
                  except OSError as exc:
                      if sock is not None:
                          sock.close()
                      exceptions.append(exc)
                  except:
                      if sock is not None:
                          sock.close()
                      raise
                  else:
                      break
              else:
                  raise exceptions[0]
  
          protocol = protocol_factory()
          waiter = self.create_future()
          transport = self._make_datagram_transport(
              sock, protocol, r_addr, waiter)
          if self._debug:
              if local_addr:
                  logger.info("Datagram endpoint local_addr=%r remote_addr=%r "
                              "created: (%r, %r)",
                              local_addr, remote_addr, transport, protocol)
              else:
                  logger.debug("Datagram endpoint remote_addr=%r created: "
                               "(%r, %r)",
                               remote_addr, transport, protocol)
  
          try:
              await waiter
          except:
              transport.close()
              raise
  
          return transport, protocol
  
      async def _ensure_resolved(self, address, *,
                                 family=0, type=socket.SOCK_STREAM,
                                 proto=0, flags=0, loop):
          host, port = address[:2]
          info = _ipaddr_info(host, port, family, type, proto)
          if info is not None:
              # "host" is already a resolved IP.
              return [info]
          else:
              return await loop.getaddrinfo(host, port, family=family, type=type,
                                            proto=proto, flags=flags)
  
      async def _create_server_getaddrinfo(self, host, port, family, flags):
          infos = await self._ensure_resolved((host, port), family=family,
                                              type=socket.SOCK_STREAM,
                                              flags=flags, loop=self)
          if not infos:
              raise OSError(f'getaddrinfo({host!r}) returned empty list')
          return infos
  
      async def create_server(
              self, protocol_factory, host=None, port=None,
              *,
              family=socket.AF_UNSPEC,
              flags=socket.AI_PASSIVE,
              sock=None,
              backlog=100,
              ssl=None,
              reuse_address=None,
              reuse_port=None,
              ssl_handshake_timeout=None,
              start_serving=True):
          """Create a TCP server.
  
          The host parameter can be a string, in that case the TCP server is
          bound to host and port.
  
          The host parameter can also be a sequence of strings and in that case
          the TCP server is bound to all hosts of the sequence. If a host
          appears multiple times (possibly indirectly e.g. when hostnames
          resolve to the same IP address), the server is only bound once to that
          host.
  
          Return a Server object which can be used to stop the service.
  
          This method is a coroutine.
          """
          if isinstance(ssl, bool):
              raise TypeError('ssl argument must be an SSLContext or None')
  
          if ssl_handshake_timeout is not None and ssl is None:
              raise ValueError(
                  'ssl_handshake_timeout is only meaningful with ssl')
  
          if host is not None or port is not None:
              if sock is not None:
                  raise ValueError(
                      'host/port and sock can not be specified at the same time')
  
              if reuse_address is None:
                  reuse_address = os.name == 'posix' and sys.platform != 'cygwin'
              sockets = []
              if host == '':
                  hosts = [None]
              elif (isinstance(host, str) or
                    not isinstance(host, collections.abc.Iterable)):
                  hosts = [host]
              else:
                  hosts = host
  
              fs = [self._create_server_getaddrinfo(host, port, family=family,
                                                    flags=flags)
                    for host in hosts]
              infos = await tasks.gather(*fs, loop=self)
              infos = set(itertools.chain.from_iterable(infos))
  
              completed = False
              try:
                  for res in infos:
                      af, socktype, proto, canonname, sa = res
                      try:
                          sock = socket.socket(af, socktype, proto)
                      except socket.error:
                          # Assume it's a bad family/type/protocol combination.
                          if self._debug:
                              logger.warning('create_server() failed to create '
                                             'socket.socket(%r, %r, %r)',
                                             af, socktype, proto, exc_info=True)
                          continue
                      sockets.append(sock)
                      if reuse_address:
                          sock.setsockopt(
                              socket.SOL_SOCKET, socket.SO_REUSEADDR, True)
                      if reuse_port:
                          _set_reuseport(sock)
                      # Disable IPv4/IPv6 dual stack support (enabled by
                      # default on Linux) which makes a single socket
                      # listen on both address families.
                      if (_HAS_IPv6 and
                              af == socket.AF_INET6 and
                              hasattr(socket, 'IPPROTO_IPV6')):
                          sock.setsockopt(socket.IPPROTO_IPV6,
                                          socket.IPV6_V6ONLY,
                                          True)
                      try:
                          sock.bind(sa)
                      except OSError as err:
                          raise OSError(err.errno, 'error while attempting '
                                        'to bind on address %r: %s'
                                        % (sa, err.strerror.lower())) from None
                  completed = True
              finally:
                  if not completed:
                      for sock in sockets:
                          sock.close()
          else:
              if sock is None:
                  raise ValueError('Neither host/port nor sock were specified')
              if sock.type != socket.SOCK_STREAM:
                  raise ValueError(f'A Stream Socket was expected, got {sock!r}')
              sockets = [sock]
  
          for sock in sockets:
              sock.setblocking(False)
  
          server = Server(self, sockets, protocol_factory,
                          ssl, backlog, ssl_handshake_timeout)
          if start_serving:
              server._start_serving()
              # Skip one loop iteration so that all 'loop.add_reader'
              # go through.
              await tasks.sleep(0, loop=self)
  
          if self._debug:
              logger.info("%r is serving", server)
          return server
  
      async def connect_accepted_socket(
              self, protocol_factory, sock,
              *, ssl=None,
              ssl_handshake_timeout=None):
          """Handle an accepted connection.
  
          This is used by servers that accept connections outside of
          asyncio but that use asyncio to handle connections.
  
          This method is a coroutine.  When completed, the coroutine
          returns a (transport, protocol) pair.
          """
          if sock.type != socket.SOCK_STREAM:
              raise ValueError(f'A Stream Socket was expected, got {sock!r}')
  
          if ssl_handshake_timeout is not None and not ssl:
              raise ValueError(
                  'ssl_handshake_timeout is only meaningful with ssl')
  
          transport, protocol = await self._create_connection_transport(
              sock, protocol_factory, ssl, '', server_side=True,
              ssl_handshake_timeout=ssl_handshake_timeout)
          if self._debug:
              # Get the socket from the transport because SSL transport closes
              # the old socket and creates a new SSL socket
              sock = transport.get_extra_info('socket')
              logger.debug("%r handled: (%r, %r)", sock, transport, protocol)
          return transport, protocol
  
      async def connect_read_pipe(self, protocol_factory, pipe):
          protocol = protocol_factory()
          waiter = self.create_future()
          transport = self._make_read_pipe_transport(pipe, protocol, waiter)
  
          try:
              await waiter
          except:
              transport.close()
              raise
  
          if self._debug:
              logger.debug('Read pipe %r connected: (%r, %r)',
                           pipe.fileno(), transport, protocol)
          return transport, protocol
  
      async def connect_write_pipe(self, protocol_factory, pipe):
          protocol = protocol_factory()
          waiter = self.create_future()
          transport = self._make_write_pipe_transport(pipe, protocol, waiter)
  
          try:
              await waiter
          except:
              transport.close()
              raise
  
          if self._debug:
              logger.debug('Write pipe %r connected: (%r, %r)',
                           pipe.fileno(), transport, protocol)
          return transport, protocol
  
      def _log_subprocess(self, msg, stdin, stdout, stderr):
          info = [msg]
          if stdin is not None:
              info.append(f'stdin={_format_pipe(stdin)}')
          if stdout is not None and stderr == subprocess.STDOUT:
              info.append(f'stdout=stderr={_format_pipe(stdout)}')
          else:
              if stdout is not None:
                  info.append(f'stdout={_format_pipe(stdout)}')
              if stderr is not None:
                  info.append(f'stderr={_format_pipe(stderr)}')
          logger.debug(' '.join(info))
  
      async def subprocess_shell(self, protocol_factory, cmd, *,
                                 stdin=subprocess.PIPE,
                                 stdout=subprocess.PIPE,
                                 stderr=subprocess.PIPE,
                                 universal_newlines=False,
                                 shell=True, bufsize=0,
                                 **kwargs):
          if not isinstance(cmd, (bytes, str)):
              raise ValueError("cmd must be a string")
          if universal_newlines:
              raise ValueError("universal_newlines must be False")
          if not shell:
              raise ValueError("shell must be True")
          if bufsize != 0:
              raise ValueError("bufsize must be 0")
          protocol = protocol_factory()
          debug_log = None
          if self._debug:
              # don't log parameters: they may contain sensitive information
              # (password) and may be too long
              debug_log = 'run shell command %r' % cmd
              self._log_subprocess(debug_log, stdin, stdout, stderr)
          transport = await self._make_subprocess_transport(
              protocol, cmd, True, stdin, stdout, stderr, bufsize, **kwargs)
          if self._debug and debug_log is not None:
              logger.info('%s: %r', debug_log, transport)
          return transport, protocol
  
      async def subprocess_exec(self, protocol_factory, program, *args,
                                stdin=subprocess.PIPE, stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE, universal_newlines=False,
                                shell=False, bufsize=0, **kwargs):
          if universal_newlines:
              raise ValueError("universal_newlines must be False")
          if shell:
              raise ValueError("shell must be False")
          if bufsize != 0:
              raise ValueError("bufsize must be 0")
          popen_args = (program,) + args
          for arg in popen_args:
              if not isinstance(arg, (str, bytes)):
                  raise TypeError(
                      f"program arguments must be a bytes or text string, "
                      f"not {type(arg).__name__}")
          protocol = protocol_factory()
          debug_log = None
          if self._debug:
              # don't log parameters: they may contain sensitive information
              # (password) and may be too long
              debug_log = f'execute program {program!r}'
              self._log_subprocess(debug_log, stdin, stdout, stderr)
          transport = await self._make_subprocess_transport(
              protocol, popen_args, False, stdin, stdout, stderr,
              bufsize, **kwargs)
          if self._debug and debug_log is not None:
              logger.info('%s: %r', debug_log, transport)
          return transport, protocol
  
      def get_exception_handler(self):
          """Return an exception handler, or None if the default one is in use.
          """
          return self._exception_handler
  
      def set_exception_handler(self, handler):
          """Set handler as the new event loop exception handler.
  
          If handler is None, the default exception handler will
          be set.
  
          If handler is a callable object, it should have a
          signature matching '(loop, context)', where 'loop'
          will be a reference to the active event loop, 'context'
          will be a dict object (see `call_exception_handler()`
          documentation for details about context).
          """
          if handler is not None and not callable(handler):
              raise TypeError(f'A callable object or None is expected, '
                              f'got {handler!r}')
          self._exception_handler = handler
  
      def default_exception_handler(self, context):
          """Default exception handler.
  
          This is called when an exception occurs and no exception
          handler is set, and can be called by a custom exception
          handler that wants to defer to the default behavior.
  
          This default handler logs the error message and other
          context-dependent information.  In debug mode, a truncated
          stack trace is also appended showing where the given object
          (e.g. a handle or future or task) was created, if any.
  
          The context parameter has the same meaning as in
          `call_exception_handler()`.
          """
          message = context.get('message')
          if not message:
              message = 'Unhandled exception in event loop'
  
          exception = context.get('exception')
          if exception is not None:
              exc_info = (type(exception), exception, exception.__traceback__)
          else:
              exc_info = False
  
          if ('source_traceback' not in context and
                  self._current_handle is not None and
                  self._current_handle._source_traceback):
              context['handle_traceback'] = \
                  self._current_handle._source_traceback
  
          log_lines = [message]
          for key in sorted(context):
              if key in {'message', 'exception'}:
                  continue
              value = context[key]
              if key == 'source_traceback':
                  tb = ''.join(traceback.format_list(value))
                  value = 'Object created at (most recent call last):\n'
                  value += tb.rstrip()
              elif key == 'handle_traceback':
                  tb = ''.join(traceback.format_list(value))
                  value = 'Handle created at (most recent call last):\n'
                  value += tb.rstrip()
              else:
                  value = repr(value)
              log_lines.append(f'{key}: {value}')
  
          logger.error('\n'.join(log_lines), exc_info=exc_info)
  
      def call_exception_handler(self, context):
          """Call the current event loop's exception handler.
  
          The context argument is a dict containing the following keys:
  
          - 'message': Error message;
          - 'exception' (optional): Exception object;
          - 'future' (optional): Future instance;
          - 'task' (optional): Task instance;
          - 'handle' (optional): Handle instance;
          - 'protocol' (optional): Protocol instance;
          - 'transport' (optional): Transport instance;
          - 'socket' (optional): Socket instance;
          - 'asyncgen' (optional): Asynchronous generator that caused
                                   the exception.
  
          New keys maybe introduced in the future.
  
          Note: do not overload this method in an event loop subclass.
          For custom exception handling, use the
          `set_exception_handler()` method.
          """
          if self._exception_handler is None:
              try:
                  self.default_exception_handler(context)
              except Exception:
                  # Second protection layer for unexpected errors
                  # in the default implementation, as well as for subclassed
                  # event loops with overloaded "default_exception_handler".
                  logger.error('Exception in default exception handler',
                               exc_info=True)
          else:
              try:
                  self._exception_handler(self, context)
              except Exception as exc:
                  # Exception in the user set custom exception handler.
                  try:
                      # Let's try default handler.
                      self.default_exception_handler({
                          'message': 'Unhandled error in exception handler',
                          'exception': exc,
                          'context': context,
                      })
                  except Exception:
                      # Guard 'default_exception_handler' in case it is
                      # overloaded.
                      logger.error('Exception in default exception handler '
                                   'while handling an unexpected error '
                                   'in custom exception handler',
                                   exc_info=True)
  
      def _add_callback(self, handle):
          """Add a Handle to _scheduled (TimerHandle) or _ready."""
          assert isinstance(handle, events.Handle), 'A Handle is required here'
          if handle._cancelled:
              return
          assert not isinstance(handle, events.TimerHandle)
          self._ready.append(handle)
  
      def _add_callback_signalsafe(self, handle):
          """Like _add_callback() but called from a signal handler."""
          self._add_callback(handle)
          self._write_to_self()
  
      def _timer_handle_cancelled(self, handle):
          """Notification that a TimerHandle has been cancelled."""
          if handle._scheduled:
              self._timer_cancelled_count += 1
  
      def _run_once(self):
          """Run one full iteration of the event loop.
  
          This calls all currently ready callbacks, polls for I/O,
          schedules the resulting callbacks, and finally schedules
          'call_later' callbacks.
          """
  
          sched_count = len(self._scheduled)
          if (sched_count > _MIN_SCHEDULED_TIMER_HANDLES and
              self._timer_cancelled_count / sched_count >
                  _MIN_CANCELLED_TIMER_HANDLES_FRACTION):
              # Remove delayed calls that were cancelled if their number
              # is too high
              new_scheduled = []
              for handle in self._scheduled:
                  if handle._cancelled:
                      handle._scheduled = False
                  else:
                      new_scheduled.append(handle)
  
              heapq.heapify(new_scheduled)
              self._scheduled = new_scheduled
              self._timer_cancelled_count = 0
          else:
              # Remove delayed calls that were cancelled from head of queue.
              while self._scheduled and self._scheduled[0]._cancelled:
                  self._timer_cancelled_count -= 1
                  handle = heapq.heappop(self._scheduled)
                  handle._scheduled = False
  
          timeout = None
          if self._ready or self._stopping:
              timeout = 0
          elif self._scheduled:
              # Compute the desired timeout.
              when = self._scheduled[0]._when
              timeout = min(max(0, when - self.time()), MAXIMUM_SELECT_TIMEOUT)
  
          event_list = self._selector.select(timeout)
          self._process_events(event_list)
  
          # Handle 'later' callbacks that are ready.
          end_time = self.time() + self._clock_resolution
          while self._scheduled:
              handle = self._scheduled[0]
              if handle._when >= end_time:
                  break
              handle = heapq.heappop(self._scheduled)
              handle._scheduled = False
              self._ready.append(handle)
  
          # This is the only place where callbacks are actually *called*.
          # All other places just add them to ready.
          # Note: We run all currently scheduled callbacks, but not any
          # callbacks scheduled by callbacks run this time around --
          # they will be run the next time (after another I/O poll).
          # Use an idiom that is thread-safe without using locks.
          ntodo = len(self._ready)
          for i in range(ntodo):
              handle = self._ready.popleft()
              if handle._cancelled:
                  continue
              if self._debug:
                  try:
                      self._current_handle = handle
                      t0 = self.time()
                      handle._run()
                      dt = self.time() - t0
                      if dt >= self.slow_callback_duration:
                          logger.warning('Executing %s took %.3f seconds',
                                         _format_handle(handle), dt)
                  finally:
                      self._current_handle = None
              else:
                  handle._run()
          handle = None  # Needed to break cycles when an exception occurs.
  
      def _set_coroutine_origin_tracking(self, enabled):
          if bool(enabled) == bool(self._coroutine_origin_tracking_enabled):
              return
  
          if enabled:
              self._coroutine_origin_tracking_saved_depth = (
                  sys.get_coroutine_origin_tracking_depth())
              sys.set_coroutine_origin_tracking_depth(
                  constants.DEBUG_STACK_DEPTH)
          else:
              sys.set_coroutine_origin_tracking_depth(
                  self._coroutine_origin_tracking_saved_depth)
  
          self._coroutine_origin_tracking_enabled = enabled
  
      def get_debug(self):
          return self._debug
  
      def set_debug(self, enabled):
          self._debug = enabled
  
          if self.is_running():
              self.call_soon_threadsafe(self._set_coroutine_origin_tracking, enabled)
  