Hackery to override the stdlib's forkserver
The stdlib insists on creating multiple forkservers and semaphore trackers for each sub-sub-process launched. This isn't ideal since it costs each `tractor` sub-actor an additional 2 more processes then necessary and is confusing when viewed as a process tree (eg. via `pstree`). The majority of the change is simply avoiding the call to `forkserver.ensure_running()` and `semaphore_tracker.ensure_running()` in `ForkServer.connect_new_process()` and instead treating the user like an adult and expecting those calls to be made *once* in the parent most process (i.e. what `multiprocessing` calls the `MainProcess`). Really a proper patch should be made against cpython which allows for similar manual management of the server along with a mechanism to communicate forkserver and semaphore tracker fd info to sub-processes such that further calls to `Process.start()` work as expected. Relates to #6forkserver_singleton
Tyler Goodlet
parent
d6d7fea708
commit
f46d5b2b62
|
|
@ -0,0 +1,275 @@
|
|||
"""
|
||||
This is near-copy of the 3.8 stdlib's ``multiprocessing.forkserver.py``
|
||||
with some hackery to prevent any more then a single forkserver and
|
||||
semaphore tracker per ``MainProcess``.
|
||||
"""
|
||||
import os
|
||||
import socket
|
||||
import signal
|
||||
import struct
|
||||
import sys
|
||||
import errno
|
||||
import selectors
|
||||
import warnings
|
||||
|
||||
from multiprocessing import (
|
||||
forkserver, semaphore_tracker, spawn, process, util
|
||||
)
|
||||
from multiprocessing.forkserver import (
|
||||
ForkServer, MAXFDS_TO_SEND, write_unsigned,
|
||||
# _serve_one,
|
||||
)
|
||||
from multiprocessing.context import reduction
|
||||
|
||||
|
||||
# taken from 3.8
|
||||
SIGNED_STRUCT = struct.Struct('q') # large enough for pid_t
|
||||
|
||||
|
||||
class AdultForkServer(ForkServer):
|
||||
|
||||
def connect_to_new_process(self, fds):
|
||||
'''Request forkserver to create a child process.
|
||||
|
||||
Returns a pair of fds (status_r, data_w). The calling process can read
|
||||
the child process's pid and (eventually) its returncode from status_r.
|
||||
The calling process should write to data_w the pickled preparation and
|
||||
process data.
|
||||
'''
|
||||
# self.ensure_running() # treat our users like adults expecting
|
||||
# them to spawn the server on their own
|
||||
if len(fds) + 4 >= MAXFDS_TO_SEND:
|
||||
raise ValueError('too many fds')
|
||||
with socket.socket(socket.AF_UNIX) as client:
|
||||
client.connect(self._forkserver_address)
|
||||
parent_r, child_w = os.pipe()
|
||||
child_r, parent_w = os.pipe()
|
||||
allfds = [child_r, child_w, self._forkserver_alive_fd,
|
||||
semaphore_tracker.getfd()]
|
||||
allfds += fds
|
||||
|
||||
# This is the only part changed
|
||||
try:
|
||||
while True:
|
||||
try:
|
||||
reduction.sendfds(client, allfds)
|
||||
break
|
||||
except OSError as err:
|
||||
if err.args[0] == 9:
|
||||
print(f"Bad FD {err}")
|
||||
client = socket.socket(socket.AF_UNIX)
|
||||
client.connect(self._forkserver_address)
|
||||
continue
|
||||
raise
|
||||
# This is the only part changed
|
||||
|
||||
return parent_r, parent_w
|
||||
except Exception:
|
||||
os.close(parent_r)
|
||||
os.close(parent_w)
|
||||
raise
|
||||
finally:
|
||||
os.close(child_r)
|
||||
os.close(child_w)
|
||||
|
||||
|
||||
def main(listener_fd, alive_r, preload, main_path=None, sys_path=None):
|
||||
'''Run forkserver.'''
|
||||
if preload:
|
||||
if '__main__' in preload and main_path is not None:
|
||||
process.current_process()._inheriting = True
|
||||
try:
|
||||
spawn.import_main_path(main_path)
|
||||
finally:
|
||||
del process.current_process()._inheriting
|
||||
for modname in preload:
|
||||
try:
|
||||
__import__(modname)
|
||||
except ImportError:
|
||||
pass
|
||||
|
||||
util._close_stdin()
|
||||
|
||||
sig_r, sig_w = os.pipe()
|
||||
os.set_blocking(sig_r, False)
|
||||
os.set_blocking(sig_w, False)
|
||||
|
||||
def sigchld_handler(*_unused):
|
||||
# Dummy signal handler, doesn't do anything
|
||||
pass
|
||||
|
||||
handlers = {
|
||||
# unblocking SIGCHLD allows the wakeup fd to notify our event loop
|
||||
signal.SIGCHLD: sigchld_handler,
|
||||
# protect the process from ^C
|
||||
signal.SIGINT: signal.SIG_IGN,
|
||||
}
|
||||
old_handlers = {sig: signal.signal(sig, val)
|
||||
for (sig, val) in handlers.items()}
|
||||
|
||||
# calling os.write() in the Python signal handler is racy
|
||||
signal.set_wakeup_fd(sig_w)
|
||||
|
||||
# map child pids to client fds
|
||||
pid_to_fd = {}
|
||||
|
||||
with socket.socket(socket.AF_UNIX, fileno=listener_fd) as listener, \
|
||||
selectors.DefaultSelector() as selector:
|
||||
_forkserver._forkserver_address = listener.getsockname()
|
||||
|
||||
selector.register(listener, selectors.EVENT_READ)
|
||||
selector.register(alive_r, selectors.EVENT_READ)
|
||||
selector.register(sig_r, selectors.EVENT_READ)
|
||||
|
||||
while True:
|
||||
try:
|
||||
while True:
|
||||
rfds = [key.fileobj for (key, events) in selector.select()]
|
||||
if rfds:
|
||||
break
|
||||
|
||||
if alive_r in rfds:
|
||||
# EOF because no more client processes left
|
||||
assert os.read(alive_r, 1) == b'', "Not at EOF?"
|
||||
raise SystemExit
|
||||
|
||||
if sig_r in rfds:
|
||||
# Got SIGCHLD
|
||||
os.read(sig_r, 65536) # exhaust
|
||||
while True:
|
||||
# Scan for child processes
|
||||
try:
|
||||
pid, sts = os.waitpid(-1, os.WNOHANG)
|
||||
except ChildProcessError:
|
||||
break
|
||||
if pid == 0:
|
||||
break
|
||||
child_w = pid_to_fd.pop(pid, None)
|
||||
if child_w is not None:
|
||||
if os.WIFSIGNALED(sts):
|
||||
returncode = -os.WTERMSIG(sts)
|
||||
else:
|
||||
if not os.WIFEXITED(sts):
|
||||
raise AssertionError(
|
||||
"Child {0:n} status is {1:n}".format(
|
||||
pid, sts))
|
||||
returncode = os.WEXITSTATUS(sts)
|
||||
# Send exit code to client process
|
||||
try:
|
||||
# write_signed(child_w, returncode)
|
||||
write_unsigned(child_w, returncode)
|
||||
except BrokenPipeError:
|
||||
# client vanished
|
||||
pass
|
||||
os.close(child_w)
|
||||
else:
|
||||
# This shouldn't happen really
|
||||
warnings.warn('forkserver: waitpid returned '
|
||||
'unexpected pid %d' % pid)
|
||||
|
||||
if listener in rfds:
|
||||
# Incoming fork request
|
||||
with listener.accept()[0] as s:
|
||||
|
||||
# Thing changed - be tolerant of socket disconnects
|
||||
try:
|
||||
# Receive fds from client
|
||||
fds = reduction.recvfds(s, MAXFDS_TO_SEND + 1)
|
||||
except EOFError:
|
||||
# broken socket due to reconnection on client-side
|
||||
continue
|
||||
# Thing changed - be tolerant of socket disconnects
|
||||
|
||||
if len(fds) > MAXFDS_TO_SEND:
|
||||
raise RuntimeError(
|
||||
"Too many ({0:n}) fds to send".format(
|
||||
len(fds)))
|
||||
child_r, child_w, *fds = fds
|
||||
s.close()
|
||||
pid = os.fork()
|
||||
if pid == 0:
|
||||
# Child
|
||||
code = 1
|
||||
try:
|
||||
listener.close()
|
||||
selector.close()
|
||||
unused_fds = [alive_r, child_w, sig_r, sig_w]
|
||||
unused_fds.extend(pid_to_fd.values())
|
||||
code = _serve_one(child_r, fds,
|
||||
unused_fds,
|
||||
old_handlers)
|
||||
except Exception:
|
||||
sys.excepthook(*sys.exc_info())
|
||||
sys.stderr.flush()
|
||||
finally:
|
||||
os._exit(code)
|
||||
else:
|
||||
# Send pid to client process
|
||||
try:
|
||||
# write_signed(child_w, pid)
|
||||
write_unsigned(child_w, pid)
|
||||
except BrokenPipeError:
|
||||
# client vanished
|
||||
pass
|
||||
pid_to_fd[pid] = child_w
|
||||
os.close(child_r)
|
||||
for fd in fds:
|
||||
os.close(fd)
|
||||
|
||||
except OSError as e:
|
||||
if e.errno != errno.ECONNABORTED:
|
||||
raise
|
||||
|
||||
|
||||
def _serve_one(child_r, fds, unused_fds, handlers):
|
||||
# close unnecessary stuff and reset signal handlers
|
||||
signal.set_wakeup_fd(-1)
|
||||
for sig, val in handlers.items():
|
||||
signal.signal(sig, val)
|
||||
for fd in unused_fds:
|
||||
os.close(fd)
|
||||
|
||||
(_forkserver._forkserver_alive_fd,
|
||||
semaphore_tracker._semaphore_tracker._fd,
|
||||
*_forkserver._inherited_fds) = fds
|
||||
|
||||
# Run process object received over pipe
|
||||
code = spawn._main(child_r)
|
||||
|
||||
return code
|
||||
|
||||
|
||||
def write_signed(fd, n):
|
||||
msg = SIGNED_STRUCT.pack(n)
|
||||
while msg:
|
||||
nbytes = os.write(fd, msg)
|
||||
if nbytes == 0:
|
||||
raise RuntimeError('should not get here')
|
||||
msg = msg[nbytes:]
|
||||
|
||||
|
||||
class AdultSemaphoreTracker(semaphore_tracker.SemaphoreTracker):
|
||||
"""Stop GD ensuring everything is running...
|
||||
"""
|
||||
def getfd(self):
|
||||
# self.ensure_running()
|
||||
return self._fd
|
||||
|
||||
|
||||
# override the stdlib's stuff
|
||||
_semaphore_tracker = AdultSemaphoreTracker()
|
||||
semaphore_tracker._semaphore_tracker = _semaphore_tracker
|
||||
semaphore_tracker.ensure_running = _semaphore_tracker.ensure_running
|
||||
semaphore_tracker.register = _semaphore_tracker.register
|
||||
semaphore_tracker.unregister = _semaphore_tracker.unregister
|
||||
semaphore_tracker.getfd = _semaphore_tracker.getfd
|
||||
|
||||
|
||||
_forkserver = AdultForkServer()
|
||||
forkserver._forkserver = _forkserver
|
||||
forkserver.main = main
|
||||
forkserver._serve_one = _serve_one
|
||||
forkserver.ensure_running = _forkserver.ensure_running
|
||||
forkserver.get_inherited_fds = _forkserver.get_inherited_fds
|
||||
forkserver.connect_to_new_process = _forkserver.connect_to_new_process
|
||||
forkserver.set_forkserver_preload = _forkserver.set_forkserver_preload
|
||||
Loading…
Reference in New Issue