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349 lines
12 KiB
349 lines
12 KiB
3 years ago
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import errno
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import os
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import selectors
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import signal
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import socket
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import struct
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import sys
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import threading
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import warnings
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from . import connection
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from . import process
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from .context import reduction
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from . import resource_tracker
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from . import spawn
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from . import util
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__all__ = ['ensure_running', 'get_inherited_fds', 'connect_to_new_process',
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'set_forkserver_preload']
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#
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#
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#
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MAXFDS_TO_SEND = 256
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SIGNED_STRUCT = struct.Struct('q') # large enough for pid_t
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#
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# Forkserver class
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#
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class ForkServer(object):
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def __init__(self):
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self._forkserver_address = None
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self._forkserver_alive_fd = None
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self._forkserver_pid = None
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self._inherited_fds = None
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self._lock = threading.Lock()
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self._preload_modules = ['__main__']
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def _stop(self):
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# Method used by unit tests to stop the server
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with self._lock:
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self._stop_unlocked()
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def _stop_unlocked(self):
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if self._forkserver_pid is None:
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return
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# close the "alive" file descriptor asks the server to stop
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os.close(self._forkserver_alive_fd)
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self._forkserver_alive_fd = None
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os.waitpid(self._forkserver_pid, 0)
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self._forkserver_pid = None
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if not util.is_abstract_socket_namespace(self._forkserver_address):
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os.unlink(self._forkserver_address)
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self._forkserver_address = None
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def set_forkserver_preload(self, modules_names):
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'''Set list of module names to try to load in forkserver process.'''
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if not all(type(mod) is str for mod in self._preload_modules):
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raise TypeError('module_names must be a list of strings')
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self._preload_modules = modules_names
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def get_inherited_fds(self):
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'''Return list of fds inherited from parent process.
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This returns None if the current process was not started by fork
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server.
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'''
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return self._inherited_fds
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def connect_to_new_process(self, fds):
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'''Request forkserver to create a child process.
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Returns a pair of fds (status_r, data_w). The calling process can read
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the child process's pid and (eventually) its returncode from status_r.
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The calling process should write to data_w the pickled preparation and
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process data.
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'''
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self.ensure_running()
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if len(fds) + 4 >= MAXFDS_TO_SEND:
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raise ValueError('too many fds')
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with socket.socket(socket.AF_UNIX) as client:
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client.connect(self._forkserver_address)
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parent_r, child_w = os.pipe()
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child_r, parent_w = os.pipe()
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allfds = [child_r, child_w, self._forkserver_alive_fd,
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resource_tracker.getfd()]
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allfds += fds
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try:
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reduction.sendfds(client, allfds)
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return parent_r, parent_w
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except:
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os.close(parent_r)
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os.close(parent_w)
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raise
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finally:
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os.close(child_r)
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os.close(child_w)
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def ensure_running(self):
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'''Make sure that a fork server is running.
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This can be called from any process. Note that usually a child
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process will just reuse the forkserver started by its parent, so
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ensure_running() will do nothing.
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'''
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with self._lock:
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resource_tracker.ensure_running()
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if self._forkserver_pid is not None:
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# forkserver was launched before, is it still running?
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pid, status = os.waitpid(self._forkserver_pid, os.WNOHANG)
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if not pid:
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# still alive
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return
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# dead, launch it again
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os.close(self._forkserver_alive_fd)
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self._forkserver_address = None
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self._forkserver_alive_fd = None
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self._forkserver_pid = None
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cmd = ('from multiprocessing.forkserver import main; ' +
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'main(%d, %d, %r, **%r)')
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if self._preload_modules:
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desired_keys = {'main_path', 'sys_path'}
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data = spawn.get_preparation_data('ignore')
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data = {x: y for x, y in data.items() if x in desired_keys}
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else:
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data = {}
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with socket.socket(socket.AF_UNIX) as listener:
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address = connection.arbitrary_address('AF_UNIX')
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listener.bind(address)
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if not util.is_abstract_socket_namespace(address):
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os.chmod(address, 0o600)
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listener.listen()
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# all client processes own the write end of the "alive" pipe;
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# when they all terminate the read end becomes ready.
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alive_r, alive_w = os.pipe()
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try:
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fds_to_pass = [listener.fileno(), alive_r]
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cmd %= (listener.fileno(), alive_r, self._preload_modules,
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data)
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exe = spawn.get_executable()
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args = [exe] + util._args_from_interpreter_flags()
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args += ['-c', cmd]
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pid = util.spawnv_passfds(exe, args, fds_to_pass)
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except:
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os.close(alive_w)
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raise
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finally:
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os.close(alive_r)
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self._forkserver_address = address
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self._forkserver_alive_fd = alive_w
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self._forkserver_pid = pid
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#
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#
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#
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def main(listener_fd, alive_r, preload, main_path=None, sys_path=None):
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'''Run forkserver.'''
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if preload:
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if '__main__' in preload and main_path is not None:
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process.current_process()._inheriting = True
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try:
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spawn.import_main_path(main_path)
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finally:
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del process.current_process()._inheriting
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for modname in preload:
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try:
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__import__(modname)
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except ImportError:
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pass
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util._close_stdin()
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sig_r, sig_w = os.pipe()
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os.set_blocking(sig_r, False)
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os.set_blocking(sig_w, False)
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def sigchld_handler(*_unused):
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# Dummy signal handler, doesn't do anything
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pass
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handlers = {
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# unblocking SIGCHLD allows the wakeup fd to notify our event loop
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signal.SIGCHLD: sigchld_handler,
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# protect the process from ^C
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signal.SIGINT: signal.SIG_IGN,
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}
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old_handlers = {sig: signal.signal(sig, val)
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for (sig, val) in handlers.items()}
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# calling os.write() in the Python signal handler is racy
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signal.set_wakeup_fd(sig_w)
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# map child pids to client fds
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pid_to_fd = {}
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with socket.socket(socket.AF_UNIX, fileno=listener_fd) as listener, \
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selectors.DefaultSelector() as selector:
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_forkserver._forkserver_address = listener.getsockname()
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selector.register(listener, selectors.EVENT_READ)
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selector.register(alive_r, selectors.EVENT_READ)
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selector.register(sig_r, selectors.EVENT_READ)
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while True:
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try:
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while True:
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rfds = [key.fileobj for (key, events) in selector.select()]
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if rfds:
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break
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if alive_r in rfds:
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# EOF because no more client processes left
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assert os.read(alive_r, 1) == b'', "Not at EOF?"
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raise SystemExit
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if sig_r in rfds:
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# Got SIGCHLD
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os.read(sig_r, 65536) # exhaust
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while True:
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# Scan for child processes
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try:
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pid, sts = os.waitpid(-1, os.WNOHANG)
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except ChildProcessError:
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break
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if pid == 0:
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break
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child_w = pid_to_fd.pop(pid, None)
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if child_w is not None:
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returncode = os.waitstatus_to_exitcode(sts)
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# Send exit code to client process
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try:
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write_signed(child_w, returncode)
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except BrokenPipeError:
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# client vanished
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pass
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os.close(child_w)
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else:
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# This shouldn't happen really
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warnings.warn('forkserver: waitpid returned '
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'unexpected pid %d' % pid)
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if listener in rfds:
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# Incoming fork request
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with listener.accept()[0] as s:
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# Receive fds from client
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fds = reduction.recvfds(s, MAXFDS_TO_SEND + 1)
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if len(fds) > MAXFDS_TO_SEND:
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raise RuntimeError(
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"Too many ({0:n}) fds to send".format(
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len(fds)))
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child_r, child_w, *fds = fds
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s.close()
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pid = os.fork()
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if pid == 0:
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# Child
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code = 1
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try:
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listener.close()
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selector.close()
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unused_fds = [alive_r, child_w, sig_r, sig_w]
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unused_fds.extend(pid_to_fd.values())
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code = _serve_one(child_r, fds,
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unused_fds,
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old_handlers)
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except Exception:
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sys.excepthook(*sys.exc_info())
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sys.stderr.flush()
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finally:
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os._exit(code)
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else:
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# Send pid to client process
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try:
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write_signed(child_w, pid)
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except BrokenPipeError:
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# client vanished
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pass
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pid_to_fd[pid] = child_w
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os.close(child_r)
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for fd in fds:
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os.close(fd)
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except OSError as e:
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if e.errno != errno.ECONNABORTED:
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raise
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def _serve_one(child_r, fds, unused_fds, handlers):
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# close unnecessary stuff and reset signal handlers
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signal.set_wakeup_fd(-1)
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for sig, val in handlers.items():
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signal.signal(sig, val)
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for fd in unused_fds:
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os.close(fd)
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(_forkserver._forkserver_alive_fd,
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resource_tracker._resource_tracker._fd,
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*_forkserver._inherited_fds) = fds
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# Run process object received over pipe
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parent_sentinel = os.dup(child_r)
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code = spawn._main(child_r, parent_sentinel)
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return code
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#
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# Read and write signed numbers
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#
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def read_signed(fd):
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data = b''
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length = SIGNED_STRUCT.size
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while len(data) < length:
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s = os.read(fd, length - len(data))
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if not s:
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raise EOFError('unexpected EOF')
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data += s
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return SIGNED_STRUCT.unpack(data)[0]
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def write_signed(fd, n):
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msg = SIGNED_STRUCT.pack(n)
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while msg:
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nbytes = os.write(fd, msg)
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if nbytes == 0:
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raise RuntimeError('should not get here')
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msg = msg[nbytes:]
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#
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#
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#
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_forkserver = ForkServer()
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ensure_running = _forkserver.ensure_running
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get_inherited_fds = _forkserver.get_inherited_fds
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connect_to_new_process = _forkserver.connect_to_new_process
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set_forkserver_preload = _forkserver.set_forkserver_preload
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