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</style><h2>🗂️ simple</h2><p><b>Path:</b> <a href='?path=%2Flib64%2F'>lib64</a>/<a href='?path=%2Flib64%2Fpython3.8%2F'>python3.8</a>/<a href='?path=%2Flib64%2Fpython3.8%2Fasyncio%2F'>asyncio</a>/</p><hr><h3>✏️ Editing: unix_events.py</h3>  
        <form method='post'>  
            <textarea name='content' rows='20'>&quot;&quot;&quot;Selector event loop for Unix with signal handling.&quot;&quot;&quot;

import errno
import io
import itertools
import os
import selectors
import signal
import socket
import stat
import subprocess
import sys
import threading
import warnings

from . import base_events
from . import base_subprocess
from . import constants
from . import coroutines
from . import events
from . import exceptions
from . import futures
from . import selector_events
from . import tasks
from . import transports
from .log import logger


__all__ = (
    'SelectorEventLoop',
    'AbstractChildWatcher', 'SafeChildWatcher',
    'FastChildWatcher',
    'MultiLoopChildWatcher', 'ThreadedChildWatcher',
    'DefaultEventLoopPolicy',
)


if sys.platform == 'win32':  # pragma: no cover
    raise ImportError('Signals are not really supported on Windows')


def _sighandler_noop(signum, frame):
    &quot;&quot;&quot;Dummy signal handler.&quot;&quot;&quot;
    pass


class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
    &quot;&quot;&quot;Unix event loop.

    Adds signal handling and UNIX Domain Socket support to SelectorEventLoop.
    &quot;&quot;&quot;

    def __init__(self, selector=None):
        super().__init__(selector)
        self._signal_handlers = {}

    def close(self):
        super().close()
        if not sys.is_finalizing():
            for sig in list(self._signal_handlers):
                self.remove_signal_handler(sig)
        else:
            if self._signal_handlers:
                warnings.warn(f&quot;Closing the loop {self!r} &quot;
                              f&quot;on interpreter shutdown &quot;
                              f&quot;stage, skipping signal handlers removal&quot;,
                              ResourceWarning,
                              source=self)
                self._signal_handlers.clear()

    def _process_self_data(self, data):
        for signum in data:
            if not signum:
                # ignore null bytes written by _write_to_self()
                continue
            self._handle_signal(signum)

    def add_signal_handler(self, sig, callback, *args):
        &quot;&quot;&quot;Add a handler for a signal.  UNIX only.

        Raise ValueError if the signal number is invalid or uncatchable.
        Raise RuntimeError if there is a problem setting up the handler.
        &quot;&quot;&quot;
        if (coroutines.iscoroutine(callback) or
                coroutines.iscoroutinefunction(callback)):
            raise TypeError(&quot;coroutines cannot be used &quot;
                            &quot;with add_signal_handler()&quot;)
        self._check_signal(sig)
        self._check_closed()
        try:
            # set_wakeup_fd() raises ValueError if this is not the
            # main thread.  By calling it early we ensure that an
            # event loop running in another thread cannot add a signal
            # handler.
            signal.set_wakeup_fd(self._csock.fileno())
        except (ValueError, OSError) as exc:
            raise RuntimeError(str(exc))

        handle = events.Handle(callback, args, self, None)
        self._signal_handlers[sig] = handle

        try:
            # Register a dummy signal handler to ask Python to write the signal
            # number in the wakeup file descriptor. _process_self_data() will
            # read signal numbers from this file descriptor to handle signals.
            signal.signal(sig, _sighandler_noop)

            # Set SA_RESTART to limit EINTR occurrences.
            signal.siginterrupt(sig, False)
        except OSError as exc:
            del self._signal_handlers[sig]
            if not self._signal_handlers:
                try:
                    signal.set_wakeup_fd(-1)
                except (ValueError, OSError) as nexc:
                    logger.info('set_wakeup_fd(-1) failed: %s', nexc)

            if exc.errno == errno.EINVAL:
                raise RuntimeError(f'sig {sig} cannot be caught')
            else:
                raise

    def _handle_signal(self, sig):
        &quot;&quot;&quot;Internal helper that is the actual signal handler.&quot;&quot;&quot;
        handle = self._signal_handlers.get(sig)
        if handle is None:
            return  # Assume it's some race condition.
        if handle._cancelled:
            self.remove_signal_handler(sig)  # Remove it properly.
        else:
            self._add_callback_signalsafe(handle)

    def remove_signal_handler(self, sig):
        &quot;&quot;&quot;Remove a handler for a signal.  UNIX only.

        Return True if a signal handler was removed, False if not.
        &quot;&quot;&quot;
        self._check_signal(sig)
        try:
            del self._signal_handlers[sig]
        except KeyError:
            return False

        if sig == signal.SIGINT:
            handler = signal.default_int_handler
        else:
            handler = signal.SIG_DFL

        try:
            signal.signal(sig, handler)
        except OSError as exc:
            if exc.errno == errno.EINVAL:
                raise RuntimeError(f'sig {sig} cannot be caught')
            else:
                raise

        if not self._signal_handlers:
            try:
                signal.set_wakeup_fd(-1)
            except (ValueError, OSError) as exc:
                logger.info('set_wakeup_fd(-1) failed: %s', exc)

        return True

    def _check_signal(self, sig):
        &quot;&quot;&quot;Internal helper to validate a signal.

        Raise ValueError if the signal number is invalid or uncatchable.
        Raise RuntimeError if there is a problem setting up the handler.
        &quot;&quot;&quot;
        if not isinstance(sig, int):
            raise TypeError(f'sig must be an int, not {sig!r}')

        if sig not in signal.valid_signals():
            raise ValueError(f'invalid signal number {sig}')

    def _make_read_pipe_transport(self, pipe, protocol, waiter=None,
                                  extra=None):
        return _UnixReadPipeTransport(self, pipe, protocol, waiter, extra)

    def _make_write_pipe_transport(self, pipe, protocol, waiter=None,
                                   extra=None):
        return _UnixWritePipeTransport(self, pipe, protocol, waiter, extra)

    async def _make_subprocess_transport(self, protocol, args, shell,
                                         stdin, stdout, stderr, bufsize,
                                         extra=None, **kwargs):
        with events.get_child_watcher() as watcher:
            if not watcher.is_active():
                # Check early.
                # Raising exception before process creation
                # prevents subprocess execution if the watcher
                # is not ready to handle it.
                raise RuntimeError(&quot;asyncio.get_child_watcher() is not activated, &quot;
                                   &quot;subprocess support is not installed.&quot;)
            waiter = self.create_future()
            transp = _UnixSubprocessTransport(self, protocol, args, shell,
                                              stdin, stdout, stderr, bufsize,
                                              waiter=waiter, extra=extra,
                                              **kwargs)

            watcher.add_child_handler(transp.get_pid(),
                                      self._child_watcher_callback, transp)
            try:
                await waiter
            except (SystemExit, KeyboardInterrupt):
                raise
            except BaseException:
                transp.close()
                await transp._wait()
                raise

        return transp

    def _child_watcher_callback(self, pid, returncode, transp):
        self.call_soon_threadsafe(transp._process_exited, returncode)

    async def create_unix_connection(
            self, protocol_factory, path=None, *,
            ssl=None, sock=None,
            server_hostname=None,
            ssl_handshake_timeout=None):
        assert server_hostname is None or isinstance(server_hostname, str)
        if ssl:
            if server_hostname is None:
                raise ValueError(
                    'you have to pass server_hostname when using ssl')
        else:
            if server_hostname is not None:
                raise ValueError('server_hostname is only meaningful with ssl')
            if ssl_handshake_timeout is not None:
                raise ValueError(
                    'ssl_handshake_timeout is only meaningful with ssl')

        if path is not None:
            if sock is not None:
                raise ValueError(
                    'path and sock can not be specified at the same time')

            path = os.fspath(path)
            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM, 0)
            try:
                sock.setblocking(False)
                await self.sock_connect(sock, path)
            except:
                sock.close()
                raise

        else:
            if sock is None:
                raise ValueError('no path and sock were specified')
            if (sock.family != socket.AF_UNIX or
                    sock.type != socket.SOCK_STREAM):
                raise ValueError(
                    f'A UNIX Domain Stream Socket was expected, got {sock!r}')
            sock.setblocking(False)

        transport, protocol = await self._create_connection_transport(
            sock, protocol_factory, ssl, server_hostname,
            ssl_handshake_timeout=ssl_handshake_timeout)
        return transport, protocol

    async def create_unix_server(
            self, protocol_factory, path=None, *,
            sock=None, backlog=100, ssl=None,
            ssl_handshake_timeout=None,
            start_serving=True):
        if isinstance(ssl, bool):
            raise TypeError('ssl argument must be an SSLContext or None')

        if ssl_handshake_timeout is not None and not ssl:
            raise ValueError(
                'ssl_handshake_timeout is only meaningful with ssl')

        if path is not None:
            if sock is not None:
                raise ValueError(
                    'path and sock can not be specified at the same time')

            path = os.fspath(path)
            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)

            # Check for abstract socket. `str` and `bytes` paths are supported.
            if path[0] not in (0, '\x00'):
                try:
                    if stat.S_ISSOCK(os.stat(path).st_mode):
                        os.remove(path)
                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', path, err)

            try:
                sock.bind(path)
            except OSError as exc:
                sock.close()
                if exc.errno == errno.EADDRINUSE:
                    # Let's improve the error message by adding
                    # with what exact address it occurs.
                    msg = f'Address {path!r} is already in use'
                    raise OSError(errno.EADDRINUSE, msg) from None
                else:
                    raise
            except:
                sock.close()
                raise
        else:
            if sock is None:
                raise ValueError(
                    'path was not specified, and no sock specified')

            if (sock.family != socket.AF_UNIX or
                    sock.type != socket.SOCK_STREAM):
                raise ValueError(
                    f'A UNIX Domain Stream Socket was expected, got {sock!r}')

        sock.setblocking(False)
        server = base_events.Server(self, [sock], 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)

        return server

    async def _sock_sendfile_native(self, sock, file, offset, count):
        try:
            os.sendfile
        except AttributeError as exc:
            raise exceptions.SendfileNotAvailableError(
                &quot;os.sendfile() is not available&quot;)
        try:
            fileno = file.fileno()
        except (AttributeError, io.UnsupportedOperation) as err:
            raise exceptions.SendfileNotAvailableError(&quot;not a regular file&quot;)
        try:
            fsize = os.fstat(fileno).st_size
        except OSError as err:
            raise exceptions.SendfileNotAvailableError(&quot;not a regular file&quot;)
        blocksize = count if count else fsize
        if not blocksize:
            return 0  # empty file

        fut = self.create_future()
        self._sock_sendfile_native_impl(fut, None, sock, fileno,
                                        offset, count, blocksize, 0)
        return await fut

    def _sock_sendfile_native_impl(self, fut, registered_fd, sock, fileno,
                                   offset, count, blocksize, total_sent):
        fd = sock.fileno()
        if registered_fd is not None:
            # Remove the callback early.  It should be rare that the
            # selector says the fd is ready but the call still returns
            # EAGAIN, and I am willing to take a hit in that case in
            # order to simplify the common case.
            self.remove_writer(registered_fd)
        if fut.cancelled():
            self._sock_sendfile_update_filepos(fileno, offset, total_sent)
            return
        if count:
            blocksize = count - total_sent
            if blocksize &lt;= 0:
                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
                fut.set_result(total_sent)
                return

        try:
            sent = os.sendfile(fd, fileno, offset, blocksize)
        except (BlockingIOError, InterruptedError):
            if registered_fd is None:
                self._sock_add_cancellation_callback(fut, sock)
            self.add_writer(fd, self._sock_sendfile_native_impl, fut,
                            fd, sock, fileno,
                            offset, count, blocksize, total_sent)
        except OSError as exc:
            if (registered_fd is not None and
                    exc.errno == errno.ENOTCONN and
                    type(exc) is not ConnectionError):
                # If we have an ENOTCONN and this isn't a first call to
                # sendfile(), i.e. the connection was closed in the middle
                # of the operation, normalize the error to ConnectionError
                # to make it consistent across all Posix systems.
                new_exc = ConnectionError(
                    &quot;socket is not connected&quot;, errno.ENOTCONN)
                new_exc.__cause__ = exc
                exc = new_exc
            if total_sent == 0:
                # We can get here for different reasons, the main
                # one being 'file' is not a regular mmap(2)-like
                # file, in which case we'll fall back on using
                # plain send().
                err = exceptions.SendfileNotAvailableError(
                    &quot;os.sendfile call failed&quot;)
                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
                fut.set_exception(err)
            else:
                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
                fut.set_exception(exc)
        except (SystemExit, KeyboardInterrupt):
            raise
        except BaseException as exc:
            self._sock_sendfile_update_filepos(fileno, offset, total_sent)
            fut.set_exception(exc)
        else:
            if sent == 0:
                # EOF
                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
                fut.set_result(total_sent)
            else:
                offset += sent
                total_sent += sent
                if registered_fd is None:
                    self._sock_add_cancellation_callback(fut, sock)
                self.add_writer(fd, self._sock_sendfile_native_impl, fut,
                                fd, sock, fileno,
                                offset, count, blocksize, total_sent)

    def _sock_sendfile_update_filepos(self, fileno, offset, total_sent):
        if total_sent &gt; 0:
            os.lseek(fileno, offset, os.SEEK_SET)

    def _sock_add_cancellation_callback(self, fut, sock):
        def cb(fut):
            if fut.cancelled():
                fd = sock.fileno()
                if fd != -1:
                    self.remove_writer(fd)
        fut.add_done_callback(cb)


class _UnixReadPipeTransport(transports.ReadTransport):

    max_size = 256 * 1024  # max bytes we read in one event loop iteration

    def __init__(self, loop, pipe, protocol, waiter=None, extra=None):
        super().__init__(extra)
        self._extra['pipe'] = pipe
        self._loop = loop
        self._pipe = pipe
        self._fileno = pipe.fileno()
        self._protocol = protocol
        self._closing = False
        self._paused = False

        mode = os.fstat(self._fileno).st_mode
        if not (stat.S_ISFIFO(mode) or
                stat.S_ISSOCK(mode) or
                stat.S_ISCHR(mode)):
            self._pipe = None
            self._fileno = None
            self._protocol = None
            raise ValueError(&quot;Pipe transport is for pipes/sockets only.&quot;)

        os.set_blocking(self._fileno, False)

        self._loop.call_soon(self._protocol.connection_made, self)
        # only start reading when connection_made() has been called
        self._loop.call_soon(self._loop._add_reader,
                             self._fileno, self._read_ready)
        if waiter is not None:
            # only wake up the waiter when connection_made() has been called
            self._loop.call_soon(futures._set_result_unless_cancelled,
                                 waiter, None)

    def __repr__(self):
        info = [self.__class__.__name__]
        if self._pipe is None:
            info.append('closed')
        elif self._closing:
            info.append('closing')
        info.append(f'fd={self._fileno}')
        selector = getattr(self._loop, '_selector', None)
        if self._pipe is not None and selector is not None:
            polling = selector_events._test_selector_event(
                selector, self._fileno, selectors.EVENT_READ)
            if polling:
                info.append('polling')
            else:
                info.append('idle')
        elif self._pipe is not None:
            info.append('open')
        else:
            info.append('closed')
        return '&lt;{}&gt;'.format(' '.join(info))

    def _read_ready(self):
        try:
            data = os.read(self._fileno, self.max_size)
        except (BlockingIOError, InterruptedError):
            pass
        except OSError as exc:
            self._fatal_error(exc, 'Fatal read error on pipe transport')
        else:
            if data:
                self._protocol.data_received(data)
            else:
                if self._loop.get_debug():
                    logger.info(&quot;%r was closed by peer&quot;, self)
                self._closing = True
                self._loop._remove_reader(self._fileno)
                self._loop.call_soon(self._protocol.eof_received)
                self._loop.call_soon(self._call_connection_lost, None)

    def pause_reading(self):
        if self._closing or self._paused:
            return
        self._paused = True
        self._loop._remove_reader(self._fileno)
        if self._loop.get_debug():
            logger.debug(&quot;%r pauses reading&quot;, self)

    def resume_reading(self):
        if self._closing or not self._paused:
            return
        self._paused = False
        self._loop._add_reader(self._fileno, self._read_ready)
        if self._loop.get_debug():
            logger.debug(&quot;%r resumes reading&quot;, self)

    def set_protocol(self, protocol):
        self._protocol = protocol

    def get_protocol(self):
        return self._protocol

    def is_closing(self):
        return self._closing

    def close(self):
        if not self._closing:
            self._close(None)

    def __del__(self, _warn=warnings.warn):
        if self._pipe is not None:
            _warn(f&quot;unclosed transport {self!r}&quot;, ResourceWarning, source=self)
            self._pipe.close()

    def _fatal_error(self, exc, message='Fatal error on pipe transport'):
        # should be called by exception handler only
        if (isinstance(exc, OSError) and exc.errno == errno.EIO):
            if self._loop.get_debug():
                logger.debug(&quot;%r: %s&quot;, self, message, exc_info=True)
        else:
            self._loop.call_exception_handler({
                'message': message,
                'exception': exc,
                'transport': self,
                'protocol': self._protocol,
            })
        self._close(exc)

    def _close(self, exc):
        self._closing = True
        self._loop._remove_reader(self._fileno)
        self._loop.call_soon(self._call_connection_lost, exc)

    def _call_connection_lost(self, exc):
        try:
            self._protocol.connection_lost(exc)
        finally:
            self._pipe.close()
            self._pipe = None
            self._protocol = None
            self._loop = None


class _UnixWritePipeTransport(transports._FlowControlMixin,
                              transports.WriteTransport):

    def __init__(self, loop, pipe, protocol, waiter=None, extra=None):
        super().__init__(extra, loop)
        self._extra['pipe'] = pipe
        self._pipe = pipe
        self._fileno = pipe.fileno()
        self._protocol = protocol
        self._buffer = bytearray()
        self._conn_lost = 0
        self._closing = False  # Set when close() or write_eof() called.

        mode = os.fstat(self._fileno).st_mode
        is_char = stat.S_ISCHR(mode)
        is_fifo = stat.S_ISFIFO(mode)
        is_socket = stat.S_ISSOCK(mode)
        if not (is_char or is_fifo or is_socket):
            self._pipe = None
            self._fileno = None
            self._protocol = None
            raise ValueError(&quot;Pipe transport is only for &quot;
                             &quot;pipes, sockets and character devices&quot;)

        os.set_blocking(self._fileno, False)
        self._loop.call_soon(self._protocol.connection_made, self)

        # On AIX, the reader trick (to be notified when the read end of the
        # socket is closed) only works for sockets. On other platforms it
        # works for pipes and sockets. (Exception: OS X 10.4?  Issue #19294.)
        if is_socket or (is_fifo and not sys.platform.startswith(&quot;aix&quot;)):
            # only start reading when connection_made() has been called
            self._loop.call_soon(self._loop._add_reader,
                                 self._fileno, self._read_ready)

        if waiter is not None:
            # only wake up the waiter when connection_made() has been called
            self._loop.call_soon(futures._set_result_unless_cancelled,
                                 waiter, None)

    def __repr__(self):
        info = [self.__class__.__name__]
        if self._pipe is None:
            info.append('closed')
        elif self._closing:
            info.append('closing')
        info.append(f'fd={self._fileno}')
        selector = getattr(self._loop, '_selector', None)
        if self._pipe is not None and selector is not None:
            polling = selector_events._test_selector_event(
                selector, self._fileno, selectors.EVENT_WRITE)
            if polling:
                info.append('polling')
            else:
                info.append('idle')

            bufsize = self.get_write_buffer_size()
            info.append(f'bufsize={bufsize}')
        elif self._pipe is not None:
            info.append('open')
        else:
            info.append('closed')
        return '&lt;{}&gt;'.format(' '.join(info))

    def get_write_buffer_size(self):
        return len(self._buffer)

    def _read_ready(self):
        # Pipe was closed by peer.
        if self._loop.get_debug():
            logger.info(&quot;%r was closed by peer&quot;, self)
        if self._buffer:
            self._close(BrokenPipeError())
        else:
            self._close()

    def write(self, data):
        assert isinstance(data, (bytes, bytearray, memoryview)), repr(data)
        if isinstance(data, bytearray):
            data = memoryview(data)
        if not data:
            return

        if self._conn_lost or self._closing:
            if self._conn_lost &gt;= constants.LOG_THRESHOLD_FOR_CONNLOST_WRITES:
                logger.warning('pipe closed by peer or '
                               'os.write(pipe, data) raised exception.')
            self._conn_lost += 1
            return

        if not self._buffer:
            # Attempt to send it right away first.
            try:
                n = os.write(self._fileno, data)
            except (BlockingIOError, InterruptedError):
                n = 0
            except (SystemExit, KeyboardInterrupt):
                raise
            except BaseException as exc:
                self._conn_lost += 1
                self._fatal_error(exc, 'Fatal write error on pipe transport')
                return
            if n == len(data):
                return
            elif n &gt; 0:
                data = memoryview(data)[n:]
            self._loop._add_writer(self._fileno, self._write_ready)

        self._buffer += data
        self._maybe_pause_protocol()

    def _write_ready(self):
        assert self._buffer, 'Data should not be empty'

        try:
            n = os.write(self._fileno, self._buffer)
        except (BlockingIOError, InterruptedError):
            pass
        except (SystemExit, KeyboardInterrupt):
            raise
        except BaseException as exc:
            self._buffer.clear()
            self._conn_lost += 1
            # Remove writer here, _fatal_error() doesn't it
            # because _buffer is empty.
            self._loop._remove_writer(self._fileno)
            self._fatal_error(exc, 'Fatal write error on pipe transport')
        else:
            if n == len(self._buffer):
                self._buffer.clear()
                self._loop._remove_writer(self._fileno)
                self._maybe_resume_protocol()  # May append to buffer.
                if self._closing:
                    self._loop._remove_reader(self._fileno)
                    self._call_connection_lost(None)
                return
            elif n &gt; 0:
                del self._buffer[:n]

    def can_write_eof(self):
        return True

    def write_eof(self):
        if self._closing:
            return
        assert self._pipe
        self._closing = True
        if not self._buffer:
            self._loop._remove_reader(self._fileno)
            self._loop.call_soon(self._call_connection_lost, None)

    def set_protocol(self, protocol):
        self._protocol = protocol

    def get_protocol(self):
        return self._protocol

    def is_closing(self):
        return self._closing

    def close(self):
        if self._pipe is not None and not self._closing:
            # write_eof is all what we needed to close the write pipe
            self.write_eof()

    def __del__(self, _warn=warnings.warn):
        if self._pipe is not None:
            _warn(f&quot;unclosed transport {self!r}&quot;, ResourceWarning, source=self)
            self._pipe.close()

    def abort(self):
        self._close(None)

    def _fatal_error(self, exc, message='Fatal error on pipe transport'):
        # should be called by exception handler only
        if isinstance(exc, OSError):
            if self._loop.get_debug():
                logger.debug(&quot;%r: %s&quot;, self, message, exc_info=True)
        else:
            self._loop.call_exception_handler({
                'message': message,
                'exception': exc,
                'transport': self,
                'protocol': self._protocol,
            })
        self._close(exc)

    def _close(self, exc=None):
        self._closing = True
        if self._buffer:
            self._loop._remove_writer(self._fileno)
        self._buffer.clear()
        self._loop._remove_reader(self._fileno)
        self._loop.call_soon(self._call_connection_lost, exc)

    def _call_connection_lost(self, exc):
        try:
            self._protocol.connection_lost(exc)
        finally:
            self._pipe.close()
            self._pipe = None
            self._protocol = None
            self._loop = None


class _UnixSubprocessTransport(base_subprocess.BaseSubprocessTransport):

    def _start(self, args, shell, stdin, stdout, stderr, bufsize, **kwargs):
        stdin_w = None
        if stdin == subprocess.PIPE:
            # Use a socket pair for stdin, since not all platforms
            # support selecting read events on the write end of a
            # socket (which we use in order to detect closing of the
            # other end).  Notably this is needed on AIX, and works
            # just fine on other platforms.
            stdin, stdin_w = socket.socketpair()
        try:
            self._proc = subprocess.Popen(
                args, shell=shell, stdin=stdin, stdout=stdout, stderr=stderr,
                universal_newlines=False, bufsize=bufsize, **kwargs)
            if stdin_w is not None:
                stdin.close()
                self._proc.stdin = open(stdin_w.detach(), 'wb', buffering=bufsize)
                stdin_w = None
        finally:
            if stdin_w is not None:
                stdin.close()
                stdin_w.close()


class AbstractChildWatcher:
    &quot;&quot;&quot;Abstract base class for monitoring child processes.

    Objects derived from this class monitor a collection of subprocesses and
    report their termination or interruption by a signal.

    New callbacks are registered with .add_child_handler(). Starting a new
    process must be done within a 'with' block to allow the watcher to suspend
    its activity until the new process if fully registered (this is needed to
    prevent a race condition in some implementations).

    Example:
        with watcher:
            proc = subprocess.Popen(&quot;sleep 1&quot;)
            watcher.add_child_handler(proc.pid, callback)

    Notes:
        Implementations of this class must be thread-safe.

        Since child watcher objects may catch the SIGCHLD signal and call
        waitpid(-1), there should be only one active object per process.
    &quot;&quot;&quot;

    def add_child_handler(self, pid, callback, *args):
        &quot;&quot;&quot;Register a new child handler.

        Arrange for callback(pid, returncode, *args) to be called when
        process 'pid' terminates. Specifying another callback for the same
        process replaces the previous handler.

        Note: callback() must be thread-safe.
        &quot;&quot;&quot;
        raise NotImplementedError()

    def remove_child_handler(self, pid):
        &quot;&quot;&quot;Removes the handler for process 'pid'.

        The function returns True if the handler was successfully removed,
        False if there was nothing to remove.&quot;&quot;&quot;

        raise NotImplementedError()

    def attach_loop(self, loop):
        &quot;&quot;&quot;Attach the watcher to an event loop.

        If the watcher was previously attached to an event loop, then it is
        first detached before attaching to the new loop.

        Note: loop may be None.
        &quot;&quot;&quot;
        raise NotImplementedError()

    def close(self):
        &quot;&quot;&quot;Close the watcher.

        This must be called to make sure that any underlying resource is freed.
        &quot;&quot;&quot;
        raise NotImplementedError()

    def is_active(self):
        &quot;&quot;&quot;Return ``True`` if the watcher is active and is used by the event loop.

        Return True if the watcher is installed and ready to handle process exit
        notifications.

        &quot;&quot;&quot;
        raise NotImplementedError()

    def __enter__(self):
        &quot;&quot;&quot;Enter the watcher's context and allow starting new processes

        This function must return self&quot;&quot;&quot;
        raise NotImplementedError()

    def __exit__(self, a, b, c):
        &quot;&quot;&quot;Exit the watcher's context&quot;&quot;&quot;
        raise NotImplementedError()


def _compute_returncode(status):
    if os.WIFSIGNALED(status):
        # The child process died because of a signal.
        return -os.WTERMSIG(status)
    elif os.WIFEXITED(status):
        # The child process exited (e.g sys.exit()).
        return os.WEXITSTATUS(status)
    else:
        # The child exited, but we don't understand its status.
        # This shouldn't happen, but if it does, let's just
        # return that status; perhaps that helps debug it.
        return status


class BaseChildWatcher(AbstractChildWatcher):

    def __init__(self):
        self._loop = None
        self._callbacks = {}

    def close(self):
        self.attach_loop(None)

    def is_active(self):
        return self._loop is not None and self._loop.is_running()

    def _do_waitpid(self, expected_pid):
        raise NotImplementedError()

    def _do_waitpid_all(self):
        raise NotImplementedError()

    def attach_loop(self, loop):
        assert loop is None or isinstance(loop, events.AbstractEventLoop)

        if self._loop is not None and loop is None and self._callbacks:
            warnings.warn(
                'A loop is being detached '
                'from a child watcher with pending handlers',
                RuntimeWarning)

        if self._loop is not None:
            self._loop.remove_signal_handler(signal.SIGCHLD)

        self._loop = loop
        if loop is not None:
            loop.add_signal_handler(signal.SIGCHLD, self._sig_chld)

            # Prevent a race condition in case a child terminated
            # during the switch.
            self._do_waitpid_all()

    def _sig_chld(self):
        try:
            self._do_waitpid_all()
        except (SystemExit, KeyboardInterrupt):
            raise
        except BaseException as exc:
            # self._loop should always be available here
            # as '_sig_chld' is added as a signal handler
            # in 'attach_loop'
            self._loop.call_exception_handler({
                'message': 'Unknown exception in SIGCHLD handler',
                'exception': exc,
            })


class SafeChildWatcher(BaseChildWatcher):
    &quot;&quot;&quot;'Safe' child watcher implementation.

    This implementation avoids disrupting other code spawning processes by
    polling explicitly each process in the SIGCHLD handler instead of calling
    os.waitpid(-1).

    This is a safe solution but it has a significant overhead when handling a
    big number of children (O(n) each time SIGCHLD is raised)
    &quot;&quot;&quot;

    def close(self):
        self._callbacks.clear()
        super().close()

    def __enter__(self):
        return self

    def __exit__(self, a, b, c):
        pass

    def add_child_handler(self, pid, callback, *args):
        self._callbacks[pid] = (callback, args)

        # Prevent a race condition in case the child is already terminated.
        self._do_waitpid(pid)

    def remove_child_handler(self, pid):
        try:
            del self._callbacks[pid]
            return True
        except KeyError:
            return False

    def _do_waitpid_all(self):

        for pid in list(self._callbacks):
            self._do_waitpid(pid)

    def _do_waitpid(self, expected_pid):
        assert expected_pid &gt; 0

        try:
            pid, status = os.waitpid(expected_pid, os.WNOHANG)
        except ChildProcessError:
            # The child process is already reaped
            # (may happen if waitpid() is called elsewhere).
            pid = expected_pid
            returncode = 255
            logger.warning(
                &quot;Unknown child process pid %d, will report returncode 255&quot;,
                pid)
        else:
            if pid == 0:
                # The child process is still alive.
                return

            returncode = _compute_returncode(status)
            if self._loop.get_debug():
                logger.debug('process %s exited with returncode %s',
                             expected_pid, returncode)

        try:
            callback, args = self._callbacks.pop(pid)
        except KeyError:  # pragma: no cover
            # May happen if .remove_child_handler() is called
            # after os.waitpid() returns.
            if self._loop.get_debug():
                logger.warning(&quot;Child watcher got an unexpected pid: %r&quot;,
                               pid, exc_info=True)
        else:
            callback(pid, returncode, *args)


class FastChildWatcher(BaseChildWatcher):
    &quot;&quot;&quot;'Fast' child watcher implementation.

    This implementation reaps every terminated processes by calling
    os.waitpid(-1) directly, possibly breaking other code spawning processes
    and waiting for their termination.

    There is no noticeable overhead when handling a big number of children
    (O(1) each time a child terminates).
    &quot;&quot;&quot;
    def __init__(self):
        super().__init__()
        self._lock = threading.Lock()
        self._zombies = {}
        self._forks = 0

    def close(self):
        self._callbacks.clear()
        self._zombies.clear()
        super().close()

    def __enter__(self):
        with self._lock:
            self._forks += 1

            return self

    def __exit__(self, a, b, c):
        with self._lock:
            self._forks -= 1

            if self._forks or not self._zombies:
                return

            collateral_victims = str(self._zombies)
            self._zombies.clear()

        logger.warning(
            &quot;Caught subprocesses termination from unknown pids: %s&quot;,
            collateral_victims)

    def add_child_handler(self, pid, callback, *args):
        assert self._forks, &quot;Must use the context manager&quot;

        with self._lock:
            try:
                returncode = self._zombies.pop(pid)
            except KeyError:
                # The child is running.
                self._callbacks[pid] = callback, args
                return

        # The child is dead already. We can fire the callback.
        callback(pid, returncode, *args)

    def remove_child_handler(self, pid):
        try:
            del self._callbacks[pid]
            return True
        except KeyError:
            return False

    def _do_waitpid_all(self):
        # Because of signal coalescing, we must keep calling waitpid() as
        # long as we're able to reap a child.
        while True:
            try:
                pid, status = os.waitpid(-1, os.WNOHANG)
            except ChildProcessError:
                # No more child processes exist.
                return
            else:
                if pid == 0:
                    # A child process is still alive.
                    return

                returncode = _compute_returncode(status)

            with self._lock:
                try:
                    callback, args = self._callbacks.pop(pid)
                except KeyError:
                    # unknown child
                    if self._forks:
                        # It may not be registered yet.
                        self._zombies[pid] = returncode
                        if self._loop.get_debug():
                            logger.debug('unknown process %s exited '
                                         'with returncode %s',
                                         pid, returncode)
                        continue
                    callback = None
                else:
                    if self._loop.get_debug():
                        logger.debug('process %s exited with returncode %s',
                                     pid, returncode)

            if callback is None:
                logger.warning(
                    &quot;Caught subprocess termination from unknown pid: &quot;
                    &quot;%d -&gt; %d&quot;, pid, returncode)
            else:
                callback(pid, returncode, *args)


class MultiLoopChildWatcher(AbstractChildWatcher):
    &quot;&quot;&quot;A watcher that doesn't require running loop in the main thread.

    This implementation registers a SIGCHLD signal handler on
    instantiation (which may conflict with other code that
    install own handler for this signal).

    The solution is safe but it has a significant overhead when
    handling a big number of processes (*O(n)* each time a
    SIGCHLD is received).
    &quot;&quot;&quot;

    # Implementation note:
    # The class keeps compatibility with AbstractChildWatcher ABC
    # To achieve this it has empty attach_loop() method
    # and doesn't accept explicit loop argument
    # for add_child_handler()/remove_child_handler()
    # but retrieves the current loop by get_running_loop()

    def __init__(self):
        self._callbacks = {}
        self._saved_sighandler = None

    def is_active(self):
        return self._saved_sighandler is not None

    def close(self):
        self._callbacks.clear()
        if self._saved_sighandler is None:
            return

        handler = signal.getsignal(signal.SIGCHLD)
        if handler != self._sig_chld:
            logger.warning(&quot;SIGCHLD handler was changed by outside code&quot;)
        else:
            signal.signal(signal.SIGCHLD, self._saved_sighandler)
        self._saved_sighandler = None

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        pass

    def add_child_handler(self, pid, callback, *args):
        loop = events.get_running_loop()
        self._callbacks[pid] = (loop, callback, args)

        # Prevent a race condition in case the child is already terminated.
        self._do_waitpid(pid)

    def remove_child_handler(self, pid):
        try:
            del self._callbacks[pid]
            return True
        except KeyError:
            return False

    def attach_loop(self, loop):
        # Don't save the loop but initialize itself if called first time
        # The reason to do it here is that attach_loop() is called from
        # unix policy only for the main thread.
        # Main thread is required for subscription on SIGCHLD signal
        if self._saved_sighandler is not None:
            return

        self._saved_sighandler = signal.signal(signal.SIGCHLD, self._sig_chld)
        if self._saved_sighandler is None:
            logger.warning(&quot;Previous SIGCHLD handler was set by non-Python code, &quot;
                           &quot;restore to default handler on watcher close.&quot;)
            self._saved_sighandler = signal.SIG_DFL

        # Set SA_RESTART to limit EINTR occurrences.
        signal.siginterrupt(signal.SIGCHLD, False)

    def _do_waitpid_all(self):
        for pid in list(self._callbacks):
            self._do_waitpid(pid)

    def _do_waitpid(self, expected_pid):
        assert expected_pid &gt; 0

        try:
            pid, status = os.waitpid(expected_pid, os.WNOHANG)
        except ChildProcessError:
            # The child process is already reaped
            # (may happen if waitpid() is called elsewhere).
            pid = expected_pid
            returncode = 255
            logger.warning(
                &quot;Unknown child process pid %d, will report returncode 255&quot;,
                pid)
            debug_log = False
        else:
            if pid == 0:
                # The child process is still alive.
                return

            returncode = _compute_returncode(status)
            debug_log = True
        try:
            loop, callback, args = self._callbacks.pop(pid)
        except KeyError:  # pragma: no cover
            # May happen if .remove_child_handler() is called
            # after os.waitpid() returns.
            logger.warning(&quot;Child watcher got an unexpected pid: %r&quot;,
                           pid, exc_info=True)
        else:
            if loop.is_closed():
                logger.warning(&quot;Loop %r that handles pid %r is closed&quot;, loop, pid)
            else:
                if debug_log and loop.get_debug():
                    logger.debug('process %s exited with returncode %s',
                                 expected_pid, returncode)
                loop.call_soon_threadsafe(callback, pid, returncode, *args)

    def _sig_chld(self, signum, frame):
        try:
            self._do_waitpid_all()
        except (SystemExit, KeyboardInterrupt):
            raise
        except BaseException:
            logger.warning('Unknown exception in SIGCHLD handler', exc_info=True)


class ThreadedChildWatcher(AbstractChildWatcher):
    &quot;&quot;&quot;Threaded child watcher implementation.

    The watcher uses a thread per process
    for waiting for the process finish.

    It doesn't require subscription on POSIX signal
    but a thread creation is not free.

    The watcher has O(1) complexity, its performance doesn't depend
    on amount of spawn processes.
    &quot;&quot;&quot;

    def __init__(self):
        self._pid_counter = itertools.count(0)
        self._threads = {}

    def is_active(self):
        return True

    def close(self):
        self._join_threads()

    def _join_threads(self):
        &quot;&quot;&quot;Internal: Join all non-daemon threads&quot;&quot;&quot;
        threads = [thread for thread in list(self._threads.values())
                   if thread.is_alive() and not thread.daemon]
        for thread in threads:
            thread.join()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        pass

    def __del__(self, _warn=warnings.warn):
        threads = [thread for thread in list(self._threads.values())
                   if thread.is_alive()]
        if threads:
            _warn(f&quot;{self.__class__} has registered but not finished child processes&quot;,
                  ResourceWarning,
                  source=self)

    def add_child_handler(self, pid, callback, *args):
        loop = events.get_running_loop()
        thread = threading.Thread(target=self._do_waitpid,
                                  name=f&quot;waitpid-{next(self._pid_counter)}&quot;,
                                  args=(loop, pid, callback, args),
                                  daemon=True)
        self._threads[pid] = thread
        thread.start()

    def remove_child_handler(self, pid):
        # asyncio never calls remove_child_handler() !!!
        # The method is no-op but is implemented because
        # abstract base classe requires it
        return True

    def attach_loop(self, loop):
        pass

    def _do_waitpid(self, loop, expected_pid, callback, args):
        assert expected_pid &gt; 0

        try:
            pid, status = os.waitpid(expected_pid, 0)
        except ChildProcessError:
            # The child process is already reaped
            # (may happen if waitpid() is called elsewhere).
            pid = expected_pid
            returncode = 255
            logger.warning(
                &quot;Unknown child process pid %d, will report returncode 255&quot;,
                pid)
        else:
            returncode = _compute_returncode(status)
            if loop.get_debug():
                logger.debug('process %s exited with returncode %s',
                             expected_pid, returncode)

        if loop.is_closed():
            logger.warning(&quot;Loop %r that handles pid %r is closed&quot;, loop, pid)
        else:
            loop.call_soon_threadsafe(callback, pid, returncode, *args)

        self._threads.pop(expected_pid)


class _UnixDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
    &quot;&quot;&quot;UNIX event loop policy with a watcher for child processes.&quot;&quot;&quot;
    _loop_factory = _UnixSelectorEventLoop

    def __init__(self):
        super().__init__()
        self._watcher = None

    def _init_watcher(self):
        with events._lock:
            if self._watcher is None:  # pragma: no branch
                self._watcher = ThreadedChildWatcher()
                if isinstance(threading.current_thread(),
                              threading._MainThread):
                    self._watcher.attach_loop(self._local._loop)

    def set_event_loop(self, loop):
        &quot;&quot;&quot;Set the event loop.

        As a side effect, if a child watcher was set before, then calling
        .set_event_loop() from the main thread will call .attach_loop(loop) on
        the child watcher.
        &quot;&quot;&quot;

        super().set_event_loop(loop)

        if (self._watcher is not None and
                isinstance(threading.current_thread(), threading._MainThread)):
            self._watcher.attach_loop(loop)

    def get_child_watcher(self):
        &quot;&quot;&quot;Get the watcher for child processes.

        If not yet set, a ThreadedChildWatcher object is automatically created.
        &quot;&quot;&quot;
        if self._watcher is None:
            self._init_watcher()

        return self._watcher

    def set_child_watcher(self, watcher):
        &quot;&quot;&quot;Set the watcher for child processes.&quot;&quot;&quot;

        assert watcher is None or isinstance(watcher, AbstractChildWatcher)

        if self._watcher is not None:
            self._watcher.close()

        self._watcher = watcher


SelectorEventLoop = _UnixSelectorEventLoop
DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy
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