Sync contrib/tools/python3 layout with upstream

* Move src/ subdir contents to the top of the layout
* Rename self-written lib -> lib2 to avoid CaseFolding warning from the VCS
* Regenerate contrib/libs/python proxy-headers accordingly
4ccc62ac1511abcf0fed14ccade38e984e088f1e

1 files changed, 1500 insertions, 0 deletions

diff --git a/contrib/tools/python3/Lib/asyncio/unix_events.py b/contrib/tools/python3/Lib/asyncio/unix_events.py
new file mode 100644
index 0000000000..f2e920ada4
--- /dev/null
+++ b/contrib/tools/python3/Lib/asyncio/unix_events.py
@@ -0,0 +1,1500 @@
+"""Selector event loop for Unix with signal handling."""
+
+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', 'PidfdChildWatcher',
+    'MultiLoopChildWatcher', 'ThreadedChildWatcher',
+    'DefaultEventLoopPolicy',
+)
+
+
+if sys.platform == 'win32':  # pragma: no cover
+    raise ImportError('Signals are not really supported on Windows')
+
+
+def _sighandler_noop(signum, frame):
+    """Dummy signal handler."""
+    pass
+
+
+def waitstatus_to_exitcode(status):
+    try:
+        return os.waitstatus_to_exitcode(status)
+    except ValueError:
+        # 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 _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
+    """Unix event loop.
+
+    Adds signal handling and UNIX Domain Socket support to SelectorEventLoop.
+    """
+
+    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"Closing the loop {self!r} "
+                              f"on interpreter shutdown "
+                              f"stage, skipping signal handlers removal",
+                              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):
+        """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.
+        """
+        if (coroutines.iscoroutine(callback) or
+                coroutines.iscoroutinefunction(callback)):
+            raise TypeError("coroutines cannot be used "
+                            "with add_signal_handler()")
+        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):
+        """Internal helper that is the actual signal handler."""
+        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):
+        """Remove a handler for a signal.  UNIX only.
+
+        Return True if a signal handler was removed, False if not.
+        """
+        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):
+        """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.
+        """
+        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 warnings.catch_warnings():
+            warnings.simplefilter('ignore', DeprecationWarning)
+            watcher = events.get_child_watcher()
+
+        with 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("asyncio.get_child_watcher() is not activated, "
+                                "subprocess support is not installed.")
+            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,
+            ssl_shutdown_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 ssl_shutdown_timeout is not None:
+                raise ValueError(
+                    'ssl_shutdown_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,
+            ssl_shutdown_timeout=ssl_shutdown_timeout)
+        return transport, protocol
+
+    async def create_unix_server(
+            self, protocol_factory, path=None, *,
+            sock=None, backlog=100, ssl=None,
+            ssl_handshake_timeout=None,
+            ssl_shutdown_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 ssl_shutdown_timeout is not None and not ssl:
+            raise ValueError(
+                'ssl_shutdown_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,
+                                    ssl_shutdown_timeout)
+        if start_serving:
+            server._start_serving()
+            # Skip one loop iteration so that all 'loop.add_reader'
+            # go through.
+            await tasks.sleep(0)
+
+        return server
+
+    async def _sock_sendfile_native(self, sock, file, offset, count):
+        try:
+            os.sendfile
+        except AttributeError:
+            raise exceptions.SendfileNotAvailableError(
+                "os.sendfile() is not available")
+        try:
+            fileno = file.fileno()
+        except (AttributeError, io.UnsupportedOperation) as err:
+            raise exceptions.SendfileNotAvailableError("not a regular file")
+        try:
+            fsize = os.fstat(fileno).st_size
+        except OSError:
+            raise exceptions.SendfileNotAvailableError("not a regular file")
+        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 <= 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(
+                    "socket is not connected", 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(
+                    "os.sendfile call failed")
+                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 > 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("Pipe transport is for pipes/sockets only.")
+
+        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._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 _add_reader(self, fd, callback):
+        if not self.is_reading():
+            return
+        self._loop._add_reader(fd, callback)
+
+    def is_reading(self):
+        return not self._paused and not self._closing
+
+    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 '<{}>'.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("%r was closed by peer", 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 not self.is_reading():
+            return
+        self._paused = True
+        self._loop._remove_reader(self._fileno)
+        if self._loop.get_debug():
+            logger.debug("%r pauses reading", 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("%r resumes reading", 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"unclosed transport {self!r}", 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("%r: %s", 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("Pipe transport is only for "
+                             "pipes, sockets and character devices")
+
+        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("aix")):
+            # 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 '<{}>'.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("%r was closed by peer", 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 >= 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 > 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 > 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"unclosed transport {self!r}", 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("%r: %s", 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 and sys.platform.startswith('aix'):
+            # Use a socket pair for stdin on AIX, since it does not
+            # support selecting read events on the write end of a
+            # socket (which we use in order to detect closing of the
+            # other end).
+            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:
+    """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("sleep 1")
+            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.
+    """
+
+    def __init_subclass__(cls) -> None:
+        if cls.__module__ != __name__:
+            warnings._deprecated("AbstractChildWatcher",
+                             "{name!r} is deprecated as of Python 3.12 and will be "
+                             "removed in Python {remove}.",
+                              remove=(3, 14))
+
+    def add_child_handler(self, pid, callback, *args):
+        """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.
+        """
+        raise NotImplementedError()
+
+    def remove_child_handler(self, pid):
+        """Removes the handler for process 'pid'.
+
+        The function returns True if the handler was successfully removed,
+        False if there was nothing to remove."""
+
+        raise NotImplementedError()
+
+    def attach_loop(self, loop):
+        """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.
+        """
+        raise NotImplementedError()
+
+    def close(self):
+        """Close the watcher.
+
+        This must be called to make sure that any underlying resource is freed.
+        """
+        raise NotImplementedError()
+
+    def is_active(self):
+        """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.
+
+        """
+        raise NotImplementedError()
+
+    def __enter__(self):
+        """Enter the watcher's context and allow starting new processes
+
+        This function must return self"""
+        raise NotImplementedError()
+
+    def __exit__(self, a, b, c):
+        """Exit the watcher's context"""
+        raise NotImplementedError()
+
+
+class PidfdChildWatcher(AbstractChildWatcher):
+    """Child watcher implementation using Linux's pid file descriptors.
+
+    This child watcher polls process file descriptors (pidfds) to await child
+    process termination. In some respects, PidfdChildWatcher is a "Goldilocks"
+    child watcher implementation. It doesn't require signals or threads, doesn't
+    interfere with any processes launched outside the event loop, and scales
+    linearly with the number of subprocesses launched by the event loop. The
+    main disadvantage is that pidfds are specific to Linux, and only work on
+    recent (5.3+) kernels.
+    """
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_traceback):
+        pass
+
+    def is_active(self):
+        return True
+
+    def close(self):
+        pass
+
+    def attach_loop(self, loop):
+        pass
+
+    def add_child_handler(self, pid, callback, *args):
+        loop = events.get_running_loop()
+        pidfd = os.pidfd_open(pid)
+        loop._add_reader(pidfd, self._do_wait, pid, pidfd, callback, args)
+
+    def _do_wait(self, pid, pidfd, callback, args):
+        loop = events.get_running_loop()
+        loop._remove_reader(pidfd)
+        try:
+            _, status = os.waitpid(pid, 0)
+        except ChildProcessError:
+            # The child process is already reaped
+            # (may happen if waitpid() is called elsewhere).
+            returncode = 255
+            logger.warning(
+                "child process pid %d exit status already read: "
+                " will report returncode 255",
+                pid)
+        else:
+            returncode = waitstatus_to_exitcode(status)
+
+        os.close(pidfd)
+        callback(pid, returncode, *args)
+
+    def remove_child_handler(self, pid):
+        # asyncio never calls remove_child_handler() !!!
+        # The method is no-op but is implemented because
+        # abstract base classes require it.
+        return True
+
+
+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):
+    """'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)
+    """
+
+    def __init__(self):
+        super().__init__()
+        warnings._deprecated("SafeChildWatcher",
+                             "{name!r} is deprecated as of Python 3.12 and will be "
+                             "removed in Python {remove}.",
+                              remove=(3, 14))
+
+    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 > 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(
+                "Unknown child process pid %d, will report returncode 255",
+                pid)
+        else:
+            if pid == 0:
+                # The child process is still alive.
+                return
+
+            returncode = waitstatus_to_exitcode(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("Child watcher got an unexpected pid: %r",
+                               pid, exc_info=True)
+        else:
+            callback(pid, returncode, *args)
+
+
+class FastChildWatcher(BaseChildWatcher):
+    """'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).
+    """
+    def __init__(self):
+        super().__init__()
+        self._lock = threading.Lock()
+        self._zombies = {}
+        self._forks = 0
+        warnings._deprecated("FastChildWatcher",
+                             "{name!r} is deprecated as of Python 3.12 and will be "
+                             "removed in Python {remove}.",
+                              remove=(3, 14))
+
+    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(
+            "Caught subprocesses termination from unknown pids: %s",
+            collateral_victims)
+
+    def add_child_handler(self, pid, callback, *args):
+        assert self._forks, "Must use the context manager"
+
+        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 = waitstatus_to_exitcode(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(
+                    "Caught subprocess termination from unknown pid: "
+                    "%d -> %d", pid, returncode)
+            else:
+                callback(pid, returncode, *args)
+
+
+class MultiLoopChildWatcher(AbstractChildWatcher):
+    """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).
+    """
+
+    # 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
+        warnings._deprecated("MultiLoopChildWatcher",
+                             "{name!r} is deprecated as of Python 3.12 and will be "
+                             "removed in Python {remove}.",
+                              remove=(3, 14))
+
+    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("SIGCHLD handler was changed by outside code")
+        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("Previous SIGCHLD handler was set by non-Python code, "
+                           "restore to default handler on watcher close.")
+            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 > 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(
+                "Unknown child process pid %d, will report returncode 255",
+                pid)
+            debug_log = False
+        else:
+            if pid == 0:
+                # The child process is still alive.
+                return
+
+            returncode = waitstatus_to_exitcode(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("Child watcher got an unexpected pid: %r",
+                           pid, exc_info=True)
+        else:
+            if loop.is_closed():
+                logger.warning("Loop %r that handles pid %r is closed", 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):
+    """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.
+    """
+
+    def __init__(self):
+        self._pid_counter = itertools.count(0)
+        self._threads = {}
+
+    def is_active(self):
+        return True
+
+    def close(self):
+        pass
+
+    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"{self.__class__} has registered but not finished child processes",
+                  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"asyncio-waitpid-{next(self._pid_counter)}",
+                                  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 classes require it.
+        return True
+
+    def attach_loop(self, loop):
+        pass
+
+    def _do_waitpid(self, loop, expected_pid, callback, args):
+        assert expected_pid > 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(
+                "Unknown child process pid %d, will report returncode 255",
+                pid)
+        else:
+            returncode = waitstatus_to_exitcode(status)
+            if loop.get_debug():
+                logger.debug('process %s exited with returncode %s',
+                             expected_pid, returncode)
+
+        if loop.is_closed():
+            logger.warning("Loop %r that handles pid %r is closed", loop, pid)
+        else:
+            loop.call_soon_threadsafe(callback, pid, returncode, *args)
+
+        self._threads.pop(expected_pid)
+
+def can_use_pidfd():
+    if not hasattr(os, 'pidfd_open'):
+        return False
+    try:
+        pid = os.getpid()
+        os.close(os.pidfd_open(pid, 0))
+    except OSError:
+        # blocked by security policy like SECCOMP
+        return False
+    return True
+
+
+class _UnixDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
+    """UNIX event loop policy with a watcher for child processes."""
+    _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
+                if can_use_pidfd():
+                    self._watcher = PidfdChildWatcher()
+                else:
+                    self._watcher = ThreadedChildWatcher()
+
+    def set_event_loop(self, loop):
+        """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.
+        """
+
+        super().set_event_loop(loop)
+
+        if (self._watcher is not None and
+                threading.current_thread() is threading.main_thread()):
+            self._watcher.attach_loop(loop)
+
+    def get_child_watcher(self):
+        """Get the watcher for child processes.
+
+        If not yet set, a ThreadedChildWatcher object is automatically created.
+        """
+        if self._watcher is None:
+            self._init_watcher()
+
+        warnings._deprecated("get_child_watcher",
+                            "{name!r} is deprecated as of Python 3.12 and will be "
+                            "removed in Python {remove}.", remove=(3, 14))
+        return self._watcher
+
+    def set_child_watcher(self, watcher):
+        """Set the watcher for child processes."""
+
+        assert watcher is None or isinstance(watcher, AbstractChildWatcher)
+
+        if self._watcher is not None:
+            self._watcher.close()
+
+        self._watcher = watcher
+        warnings._deprecated("set_child_watcher",
+                            "{name!r} is deprecated as of Python 3.12 and will be "
+                            "removed in Python {remove}.", remove=(3, 14))
+
+
+SelectorEventLoop = _UnixSelectorEventLoop
+DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy