cpython/Lib/multiprocessing/forkserver.py

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import errno
import os
import selectors
import signal
import socket
import struct
import sys
import threading
from . import connection
from . import process
from . import reduction
from . import semaphore_tracker
from . import spawn
from . import util
__all__ = ['ensure_running', 'get_inherited_fds', 'connect_to_new_process',
'set_forkserver_preload']
#
#
#
MAXFDS_TO_SEND = 256
UNSIGNED_STRUCT = struct.Struct('Q') # large enough for pid_t
_forkserver_address = None
_forkserver_alive_fd = None
_inherited_fds = None
_lock = threading.Lock()
_preload_modules = ['__main__']
#
# Public function
#
def set_forkserver_preload(modules_names):
'''Set list of module names to try to load in forkserver process.'''
global _preload_modules
_preload_modules = modules_names
def get_inherited_fds():
'''Return list of fds inherited from parent process.
This returns None if the current process was not started by fork server.
'''
return _inherited_fds
def connect_to_new_process(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.
'''
if len(fds) + 4 >= MAXFDS_TO_SEND:
raise ValueError('too many fds')
with socket.socket(socket.AF_UNIX) as client:
client.connect(_forkserver_address)
parent_r, child_w = os.pipe()
child_r, parent_w = os.pipe()
allfds = [child_r, child_w, _forkserver_alive_fd,
semaphore_tracker._semaphore_tracker_fd]
allfds += fds
try:
reduction.sendfds(client, allfds)
return parent_r, parent_w
except:
os.close(parent_r)
os.close(parent_w)
raise
finally:
os.close(child_r)
os.close(child_w)
def ensure_running():
'''Make sure that a fork server is running.
This can be called from any process. Note that usually a child
process will just reuse the forkserver started by its parent, so
ensure_running() will do nothing.
'''
global _forkserver_address, _forkserver_alive_fd
with _lock:
if _forkserver_alive_fd is not None:
return
assert all(type(mod) is str for mod in _preload_modules)
cmd = ('from multiprocessing.forkserver import main; ' +
'main(%d, %d, %r, **%r)')
if _preload_modules:
desired_keys = {'main_path', 'sys_path'}
data = spawn.get_preparation_data('ignore')
data = dict((x,y) for (x,y) in data.items() if x in desired_keys)
else:
data = {}
with socket.socket(socket.AF_UNIX) as listener:
address = connection.arbitrary_address('AF_UNIX')
listener.bind(address)
os.chmod(address, 0o600)
listener.listen(100)
# all client processes own the write end of the "alive" pipe;
# when they all terminate the read end becomes ready.
alive_r, alive_w = os.pipe()
try:
fds_to_pass = [listener.fileno(), alive_r]
cmd %= (listener.fileno(), alive_r, _preload_modules, data)
exe = spawn.get_executable()
args = [exe] + util._args_from_interpreter_flags() + ['-c', cmd]
pid = util.spawnv_passfds(exe, args, fds_to_pass)
except:
os.close(alive_w)
raise
finally:
os.close(alive_r)
_forkserver_address = address
_forkserver_alive_fd = alive_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
# close sys.stdin
if sys.stdin is not None:
try:
sys.stdin.close()
sys.stdin = open(os.devnull)
except (OSError, ValueError):
pass
# ignoring SIGCHLD means no need to reap zombie processes
handler = signal.signal(signal.SIGCHLD, signal.SIG_IGN)
with socket.socket(socket.AF_UNIX, fileno=listener_fd) as listener, \
selectors.DefaultSelector() as selector:
global _forkserver_address
_forkserver_address = listener.getsockname()
selector.register(listener, selectors.EVENT_READ)
selector.register(alive_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''
raise SystemExit
assert listener in rfds
with listener.accept()[0] as s:
code = 1
if os.fork() == 0:
try:
_serve_one(s, listener, alive_r, handler)
except Exception:
sys.excepthook(*sys.exc_info())
sys.stderr.flush()
finally:
os._exit(code)
except InterruptedError:
pass
except OSError as e:
if e.errno != errno.ECONNABORTED:
raise
#
# Code to bootstrap new process
#
def _serve_one(s, listener, alive_r, handler):
global _inherited_fds, _forkserver_alive_fd
# close unnecessary stuff and reset SIGCHLD handler
listener.close()
os.close(alive_r)
signal.signal(signal.SIGCHLD, handler)
# receive fds from parent process
fds = reduction.recvfds(s, MAXFDS_TO_SEND + 1)
s.close()
assert len(fds) <= MAXFDS_TO_SEND
child_r, child_w, _forkserver_alive_fd, stfd, *_inherited_fds = fds
semaphore_tracker._semaphore_tracker_fd = stfd
# send pid to client processes
write_unsigned(child_w, os.getpid())
# reseed random number generator
if 'random' in sys.modules:
import random
random.seed()
# run process object received over pipe
code = spawn._main(child_r)
# write the exit code to the pipe
write_unsigned(child_w, code)
#
# Read and write unsigned numbers
#
def read_unsigned(fd):
data = b''
length = UNSIGNED_STRUCT.size
while len(data) < length:
while True:
try:
s = os.read(fd, length - len(data))
except InterruptedError:
pass
else:
break
if not s:
raise EOFError('unexpected EOF')
data += s
return UNSIGNED_STRUCT.unpack(data)[0]
def write_unsigned(fd, n):
msg = UNSIGNED_STRUCT.pack(n)
while msg:
while True:
try:
nbytes = os.write(fd, msg)
except InterruptedError:
pass
else:
break
if nbytes == 0:
raise RuntimeError('should not get here')
msg = msg[nbytes:]