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base_events.py72.5 KB · 1931 lines
"""Base implementation of event loop. The event loop can be broken up into a multiplexer (the partresponsible 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 positionalarguments will be passed to the callback if/when it is called.  Thisavoids the proliferation of trivial lambdas implementing closures.Keyword arguments for the callback are not supported; this is aconscious design decision, leaving the door open for keyword argumentsto modify the meaning of the API call itself.""" import collectionsimport collections.abcimport concurrent.futuresimport functoolsimport heapqimport itertoolsimport osimport socketimport statimport subprocessimport threadingimport timeimport tracebackimport sysimport warningsimport weakref try:    import sslexcept ImportError:  # pragma: no cover    ssl = None from . import constantsfrom . import coroutinesfrom . import eventsfrom . import exceptionsfrom . import futuresfrom . import protocolsfrom . import sslprotofrom . import staggeredfrom . import tasksfrom . import transportsfrom . import trsockfrom .log import logger  __all__ = 'BaseEventLoop','Server',  # 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  _HAS_IPv6 = hasattr(socket, 'AF_INET6') # Maximum timeout passed to select to avoid OS limitationsMAXIMUM_SELECT_TIMEOUT = 24 * 3600 # Used for deprecation and removal of `loop.create_datagram_endpoint()`'s# *reuse_address* parameter_unset = object()  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, flowinfo=0, scopeid=0):    # 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, flowinfo, scopeid)            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, (SystemExit, KeyboardInterrupt)):            # 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  def _check_ssl_socket(sock):    if ssl is not None and isinstance(sock, ssl.SSLSocket):        raise TypeError("Socket cannot be of type SSLSocket")  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 tuple(trsock.TransportSocket(s) for s in 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)     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        # Set to True when `loop.shutdown_default_executor` is called.        self._executor_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 _check_default_executor(self):        if self._executor_shutdown_called:            raise RuntimeError('Executor shutdown has been called')     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                })     async def shutdown_default_executor(self):        """Schedule the shutdown of the default executor."""        self._executor_shutdown_called = True        if self._default_executor is None:            return        future = self.create_future()        thread = threading.Thread(target=self._do_shutdown, args=(future,))        thread.start()        try:            await future        finally:            thread.join()     def _do_shutdown(self, future):        try:            self._default_executor.shutdown(wait=True)            self.call_soon_threadsafe(future.set_result, None)        except Exception as ex:            self.call_soon_threadsafe(future.set_exception, ex)     def _check_running(self):        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')     def run_forever(self):        """Run until stop() is called."""        self._check_closed()        self._check_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()        self._check_running()         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()        self._executor_shutdown_called = True        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            # Only check when the default executor is being used            self._check_default_executor()            if executor is None:                executor = concurrent.futures.ThreadPoolExecutor(                    thread_name_prefix='asyncio'                )                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")        _check_ssl_socket(sock)        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} "            f"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[:read])                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 sock is not None:            _check_ssl_socket(sock)         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 = await self.run_in_executor(None, file.readinto, view)                if not read:                    return total_sent  # EOF                await proto.drain()                transp.write(view[:read])                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 BaseException:            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=_unset, 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_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:                        if not (isinstance(addr, tuple) and len(addr) == 2):                            raise TypeError('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 = []             # bpo-37228            if reuse_address is not _unset:                if reuse_address:                    raise ValueError("Passing `reuse_address=True` is no "                                     "longer supported, as the usage of "                                     "SO_REUSEPORT in UDP poses a significant "                                     "security concern.")                else:                    warnings.warn("The *reuse_address* parameter has been "                                  "deprecated as of 3.5.10 and is scheduled "                                  "for removal in 3.11.", DeprecationWarning,                                  stacklevel=2)             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_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, *address[2:])        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 sock is not None:            _check_ssl_socket(sock)         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)         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')         if sock is not None:            _check_ssl_socket(sock)         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,                               encoding=None, errors=None, text=None,                               **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")        if text:            raise ValueError("text must be False")        if encoding is not None:            raise ValueError("encoding must be None")        if errors is not None:            raise ValueError("errors must be None")         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,                              encoding=None, errors=None, text=None,                              **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")        if text:            raise ValueError("text must be False")        if encoding is not None:            raise ValueError("encoding must be None")        if errors is not None:            raise ValueError("errors must be None")         popen_args = (program,) + args        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 (SystemExit, KeyboardInterrupt):                raise            except BaseException:                # 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 (SystemExit, KeyboardInterrupt):                raise            except BaseException 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 (SystemExit, KeyboardInterrupt):                    raise                except BaseException:                    # 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)