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 class
#

class ForkServer(object):

def __init__(self):
self._forkserver_address = None
self._forkserver_alive_fd = None
self._inherited_fds = None
self._lock = threading.Lock()
self._preload_modules = ['__main__']

def set_forkserver_preload(self, modules_names):
'''Set list of module names to try to load in forkserver process.'''
if not all(type(mod) is str for mod in self._preload_modules):
raise TypeError('module_names must be a list of strings')
self._preload_modules = modules_names

def get_inherited_fds(self):
'''Return list of fds inherited from parent process.

This returns None if the current process was not started by fork
server.
'''
return self._inherited_fds

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()
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
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(self):
'''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.
'''
with self._lock:
semaphore_tracker.ensure_running()
if self._forkserver_alive_fd is not None:
return

cmd = ('from multiprocessing.forkserver import main; ' +
'main(%d, %d, %r, **%r)')

if self._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, self._preload_modules,
data)
exe = spawn.get_executable()
args = [exe] + util._args_from_interpreter_flags()
args += ['-c', cmd]
pid = util.spawnv_passfds(exe, args, fds_to_pass)
except:
os.close(alive_w)
raise
finally:
os.close(alive_r)
self._forkserver_address = address
self._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:
_forkserver._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

def _serve_one(s, listener, alive_r, handler):
# 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._forkserver_alive_fd,
stfd, *_forkserver._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:]

#
#
#

_forkserver = ForkServer()
ensure_running = _forkserver.ensure_running
get_inherited_fds = _forkserver.get_inherited_fds
connect_to_new_process = _forkserver.connect_to_new_process
set_forkserver_preload = _forkserver.set_forkserver_preload