X-Git-Url: https://git.josue.xyz/?p=dotfiles%2F.git;a=blobdiff_plain;f=.local%2Flib%2Fpython2.7%2Fsite-packages%2Ftrollius%2Funix_events.py;fp=.local%2Flib%2Fpython2.7%2Fsite-packages%2Ftrollius%2Funix_events.py;h=cdefacad0b4886a8a6cd71c9d694fef4861366fb;hp=0000000000000000000000000000000000000000;hb=be62f45026507330c54b0d3ace90aceb312e1841;hpb=812379a745a7f23788c538f26d71c84232bf09cc

diff --git a/.local/lib/python2.7/site-packages/trollius/unix_events.py b/.local/lib/python2.7/site-packages/trollius/unix_events.py
new file mode 100644
index 00000000..cdefacad
--- /dev/null
+++ b/.local/lib/python2.7/site-packages/trollius/unix_events.py
@@ -0,0 +1,1034 @@
+"""Selector event loop for Unix with signal handling."""
+from __future__ import absolute_import
+
+import errno
+import os
+import signal
+import socket
+import stat
+import subprocess
+import sys
+import threading
+import warnings
+
+
+from . import base_events
+from . import base_subprocess
+from . import compat
+from . import constants
+from . import coroutines
+from . import events
+from . import futures
+from . import selector_events
+from . import selectors
+from . import transports
+from .compat import flatten_bytes
+from .coroutines import coroutine, From, Return
+from .log import logger
+from .py33_exceptions import (
+    reraise, wrap_error,
+    BlockingIOError, BrokenPipeError, ConnectionResetError,
+    InterruptedError, ChildProcessError)
+
+
+__all__ = ['SelectorEventLoop',
+           'AbstractChildWatcher', 'SafeChildWatcher',
+           'FastChildWatcher', 'DefaultEventLoopPolicy',
+           ]
+
+if sys.platform == 'win32':  # pragma: no cover
+    raise ImportError('Signals are not really supported on Windows')
+
+
+if compat.PY33:
+    def _sighandler_noop(signum, frame):
+        """Dummy signal handler."""
+        pass
+
+
+class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
+    """Unix event loop.
+
+    Adds signal handling and UNIX Domain Socket support to SelectorEventLoop.
+    """
+
+    def __init__(self, selector=None):
+        super(_UnixSelectorEventLoop, self).__init__(selector)
+        self._signal_handlers = {}
+
+    def _socketpair(self):
+        return socket.socketpair()
+
+    def close(self):
+        super(_UnixSelectorEventLoop, self).close()
+        for sig in list(self._signal_handlers):
+            self.remove_signal_handler(sig)
+
+    # On Python <= 3.2, the C signal handler of Python writes a null byte into
+    # the wakeup file descriptor. We cannot retrieve the signal numbers from
+    # the file descriptor.
+    if compat.PY33:
+        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)
+        self._signal_handlers[sig] = handle
+
+        try:
+            if compat.PY33:
+                # On Python 3.3 and newer, the C signal handler writes the
+                # signal number into the wakeup file descriptor and then calls
+                # Py_AddPendingCall() to schedule the Python signal handler.
+                #
+                # Register a dummy signal handler to ask Python to write the
+                # signal number into the wakup file descriptor.
+                # _process_self_data() will read signal numbers from this file
+                # descriptor to handle signals.
+                signal.signal(sig, _sighandler_noop)
+            else:
+                # On Python 3.2 and older, the C signal handler first calls
+                # Py_AddPendingCall() to schedule the Python signal handler,
+                # and then write a null byte into the wakeup file descriptor.
+                signal.signal(sig, self._handle_signal)
+
+            # Set SA_RESTART to limit EINTR occurrences.
+            signal.siginterrupt(sig, False)
+        except (RuntimeError, OSError) as exc:
+            # On Python 2, signal.signal(signal.SIGKILL, signal.SIG_IGN) raises
+            # RuntimeError(22, 'Invalid argument'). On Python 3,
+            # OSError(22, 'Invalid argument') is raised instead.
+            exc_type, exc_value, tb = sys.exc_info()
+
+            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 isinstance(exc, RuntimeError) or exc.errno == errno.EINVAL:
+                raise RuntimeError('sig {0} cannot be caught'.format(sig))
+            else:
+                reraise(exc_type, exc_value, tb)
+
+    def _handle_signal(self, sig, frame=None):
+        """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('sig {0} cannot be caught'.format(sig))
+            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('sig must be an int, not {0!r}'.format(sig))
+
+        if not (1 <= sig < signal.NSIG):
+            raise ValueError(
+                'sig {0} out of range(1, {1})'.format(sig, signal.NSIG))
+
+    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)
+
+    @coroutine
+    def _make_subprocess_transport(self, protocol, args, shell,
+                                   stdin, stdout, stderr, bufsize,
+                                   extra=None, **kwargs):
+        with events.get_child_watcher() as watcher:
+            waiter = futures.Future(loop=self)
+            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:
+                yield From(waiter)
+            except Exception as exc:
+                # Workaround CPython bug #23353: using yield/yield-from in an
+                # except block of a generator doesn't clear properly
+                # sys.exc_info()
+                err = exc
+            else:
+                err = None
+
+            if err is not None:
+                transp.close()
+                yield From(transp._wait())
+                raise err
+
+        raise Return(transp)
+
+    def _child_watcher_callback(self, pid, returncode, transp):
+        self.call_soon_threadsafe(transp._process_exited, returncode)
+
+    @coroutine
+    def create_unix_connection(self, protocol_factory, path,
+                               ssl=None, sock=None,
+                               server_hostname=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 path is not None:
+            if sock is not None:
+                raise ValueError(
+                    'path and sock can not be specified at the same time')
+
+            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM, 0)
+            try:
+                sock.setblocking(False)
+                yield From(self.sock_connect(sock, path))
+            except:
+                sock.close()
+                raise
+
+        else:
+            if sock is None:
+                raise ValueError('no path and sock were specified')
+            sock.setblocking(False)
+
+        transport, protocol = yield From(self._create_connection_transport(
+            sock, protocol_factory, ssl, server_hostname))
+        raise Return(transport, protocol)
+
+    @coroutine
+    def create_unix_server(self, protocol_factory, path=None,
+                           sock=None, backlog=100, ssl=None):
+        if isinstance(ssl, bool):
+            raise TypeError('ssl argument must be an SSLContext or None')
+
+        if path is not None:
+            if sock is not None:
+                raise ValueError(
+                    'path and sock can not be specified at the same time')
+
+            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+
+            try:
+                sock.bind(path)
+            except socket.error as exc:
+                sock.close()
+                if exc.errno == errno.EADDRINUSE:
+                    # Let's improve the error message by adding
+                    # with what exact address it occurs.
+                    msg = 'Address {0!r} is already in use'.format(path)
+                    raise OSError(errno.EADDRINUSE, msg)
+                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:
+                raise ValueError(
+                    'A UNIX Domain Socket was expected, got {0!r}'.format(sock))
+
+        server = base_events.Server(self, [sock])
+        sock.listen(backlog)
+        sock.setblocking(False)
+        self._start_serving(protocol_factory, sock, ssl, server)
+        return server
+
+
+if hasattr(os, 'set_blocking'):
+    # Python 3.5 and newer
+    def _set_nonblocking(fd):
+        os.set_blocking(fd, False)
+else:
+    import fcntl
+
+    def _set_nonblocking(fd):
+        flags = fcntl.fcntl(fd, fcntl.F_GETFL)
+        flags = flags | os.O_NONBLOCK
+        fcntl.fcntl(fd, fcntl.F_SETFL, flags)
+
+
+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(_UnixReadPipeTransport, self).__init__(extra)
+        self._extra['pipe'] = pipe
+        self._loop = loop
+        self._pipe = pipe
+        self._fileno = pipe.fileno()
+        mode = os.fstat(self._fileno).st_mode
+        if not (stat.S_ISFIFO(mode) or
+                stat.S_ISSOCK(mode) or
+                stat.S_ISCHR(mode)):
+            raise ValueError("Pipe transport is for pipes/sockets only.")
+        _set_nonblocking(self._fileno)
+        self._protocol = protocol
+        self._closing = 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(waiter._set_result_unless_cancelled, None)
+
+    def __repr__(self):
+        info = [self.__class__.__name__]
+        if self._pipe is None:
+            info.append('closed')
+        elif self._closing:
+            info.append('closing')
+        info.append('fd=%s' % self._fileno)
+        if self._pipe is not None:
+            polling = selector_events._test_selector_event(
+                          self._loop._selector,
+                          self._fileno, selectors.EVENT_READ)
+            if polling:
+                info.append('polling')
+            else:
+                info.append('idle')
+        else:
+            info.append('closed')
+        return '<%s>' % ' '.join(info)
+
+    def _read_ready(self):
+        try:
+            data = wrap_error(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):
+        self._loop.remove_reader(self._fileno)
+
+    def resume_reading(self):
+        self._loop.add_reader(self._fileno, self._read_ready)
+
+    def close(self):
+        if not self._closing:
+            self._close(None)
+
+    # On Python 3.3 and older, objects with a destructor part of a reference
+    # cycle are never destroyed. It's not more the case on Python 3.4 thanks
+    # to the PEP 442.
+    if compat.PY34:
+        def __del__(self):
+            if self._pipe is not None:
+                warnings.warn("unclosed transport %r" % self, ResourceWarning)
+                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(_UnixWritePipeTransport, self).__init__(extra, loop)
+        self._extra['pipe'] = pipe
+        self._pipe = pipe
+        self._fileno = pipe.fileno()
+        mode = os.fstat(self._fileno).st_mode
+        is_socket = stat.S_ISSOCK(mode)
+        if not (is_socket or
+                stat.S_ISFIFO(mode) or
+                stat.S_ISCHR(mode)):
+            raise ValueError("Pipe transport is only for "
+                             "pipes, sockets and character devices")
+        _set_nonblocking(self._fileno)
+        self._protocol = protocol
+        self._buffer = []
+        self._conn_lost = 0
+        self._closing = False  # Set when close() or write_eof() called.
+
+        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 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(waiter._set_result_unless_cancelled, None)
+
+    def __repr__(self):
+        info = [self.__class__.__name__]
+        if self._pipe is None:
+            info.append('closed')
+        elif self._closing:
+            info.append('closing')
+        info.append('fd=%s' % self._fileno)
+        if self._pipe is not None:
+            polling = selector_events._test_selector_event(
+                          self._loop._selector,
+                          self._fileno, selectors.EVENT_WRITE)
+            if polling:
+                info.append('polling')
+            else:
+                info.append('idle')
+
+            bufsize = self.get_write_buffer_size()
+            info.append('bufsize=%s' % bufsize)
+        else:
+            info.append('closed')
+        return '<%s>' % ' '.join(info)
+
+    def get_write_buffer_size(self):
+        return sum(len(data) for data in 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):
+        data = flatten_bytes(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 = wrap_error(os.write, self._fileno, data)
+            except (BlockingIOError, InterruptedError):
+                n = 0
+            except Exception 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 = data[n:]
+            self._loop.add_writer(self._fileno, self._write_ready)
+
+        self._buffer.append(data)
+        self._maybe_pause_protocol()
+
+    def _write_ready(self):
+        data = b''.join(self._buffer)
+        assert data, 'Data should not be empty'
+
+        del self._buffer[:]
+        try:
+            n = wrap_error(os.write, self._fileno, data)
+        except (BlockingIOError, InterruptedError):
+            self._buffer.append(data)
+        except Exception as exc:
+            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(data):
+                self._loop.remove_writer(self._fileno)
+                self._maybe_resume_protocol()  # May append to buffer.
+                if not self._buffer and self._closing:
+                    self._loop.remove_reader(self._fileno)
+                    self._call_connection_lost(None)
+                return
+            elif n > 0:
+                data = data[n:]
+
+            self._buffer.append(data)  # Try again later.
+
+    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 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()
+
+    # On Python 3.3 and older, objects with a destructor part of a reference
+    # cycle are never destroyed. It's not more the case on Python 3.4 thanks
+    # to the PEP 442.
+    if compat.PY34:
+        def __del__(self):
+            if self._pipe is not None:
+                warnings.warn("unclosed transport %r" % self, ResourceWarning)
+                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, (BrokenPipeError, ConnectionResetError)):
+            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)
+        del self._buffer[:]
+        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
+
+
+if hasattr(os, 'set_inheritable'):
+    # Python 3.4 and newer
+    _set_inheritable = os.set_inheritable
+else:
+    import fcntl
+
+    def _set_inheritable(fd, inheritable):
+        cloexec_flag = getattr(fcntl, 'FD_CLOEXEC', 1)
+
+        old = fcntl.fcntl(fd, fcntl.F_GETFD)
+        if not inheritable:
+            fcntl.fcntl(fd, fcntl.F_SETFD, old | cloexec_flag)
+        else:
+            fcntl.fcntl(fd, fcntl.F_SETFD, old & ~cloexec_flag)
+
+
+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 = self._loop._socketpair()
+
+            # Mark the write end of the stdin pipe as non-inheritable,
+            # needed by close_fds=False on Python 3.3 and older
+            # (Python 3.4 implements the PEP 446, socketpair returns
+            # non-inheritable sockets)
+            _set_inheritable(stdin_w.fileno(), False)
+        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:
+            # Retrieve the file descriptor from stdin_w, stdin_w should not
+            # "own" the file descriptor anymore: closing stdin_fd file
+            # descriptor must close immediatly the file
+            stdin.close()
+            if hasattr(stdin_w, 'detach'):
+                stdin_fd = stdin_w.detach()
+                self._proc.stdin = os.fdopen(stdin_fd, 'wb', bufsize)
+            else:
+                stdin_dup = os.dup(stdin_w.fileno())
+                stdin_w.close()
+                self._proc.stdin = os.fdopen(stdin_dup, 'wb', bufsize)
+
+
+class AbstractChildWatcher(object):
+    """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 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 __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 BaseChildWatcher(AbstractChildWatcher):
+
+    def __init__(self):
+        self._loop = None
+
+    def close(self):
+        self.attach_loop(None)
+
+    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:
+            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 Exception 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,
+            })
+
+    def _compute_returncode(self, 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 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(SafeChildWatcher, self).__init__()
+        self._callbacks = {}
+
+    def close(self):
+        self._callbacks.clear()
+        super(SafeChildWatcher, self).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 = self._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("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(FastChildWatcher, self).__init__()
+        self._callbacks = {}
+        self._lock = threading.Lock()
+        self._zombies = {}
+        self._forks = 0
+
+    def close(self):
+        self._callbacks.clear()
+        self._zombies.clear()
+        super(FastChildWatcher, self).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 = wrap_error(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 = self._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(
+                    "Caught subprocess termination from unknown pid: "
+                    "%d -> %d", pid, returncode)
+            else:
+                callback(pid, returncode, *args)
+
+
+class _UnixDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
+    """UNIX event loop policy with a watcher for child processes."""
+    _loop_factory = _UnixSelectorEventLoop
+
+    def __init__(self):
+        super(_UnixDefaultEventLoopPolicy, self).__init__()
+        self._watcher = None
+
+    def _init_watcher(self):
+        with events._lock:
+            if self._watcher is None:  # pragma: no branch
+                self._watcher = SafeChildWatcher()
+                if isinstance(threading.current_thread(),
+                              threading._MainThread):
+                    self._watcher.attach_loop(self._local._loop)
+
+    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(_UnixDefaultEventLoopPolicy, self).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):
+        """Get the watcher for child processes.
+
+        If not yet set, a SafeChildWatcher object is automatically created.
+        """
+        if self._watcher is None:
+            self._init_watcher()
+
+        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
+
+SelectorEventLoop = _UnixSelectorEventLoop
+DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy