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# Copyright 2018 gRPC authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
import os
import threading
_LOGGER = logging.getLogger(__name__)
_AWAIT_THREADS_TIMEOUT_SECONDS = 5
_TRUE_VALUES = ['yes', 'Yes', 'YES', 'true', 'True', 'TRUE', '1']
# This flag enables experimental support within gRPC Python for applications
# that will fork() without exec(). When enabled, gRPC Python will attempt to
# pause all of its internally created threads before the fork syscall proceeds.
#
# For this to be successful, the application must not have multiple threads of
# its own calling into gRPC when fork is invoked. Any callbacks from gRPC
# Python-spawned threads into user code (e.g., callbacks for asynchronous RPCs)
# must not block and should execute quickly.
#
# This flag is not supported on Windows.
_GRPC_ENABLE_FORK_SUPPORT = (
os.environ.get('GRPC_ENABLE_FORK_SUPPORT', '0')
.lower() in _TRUE_VALUES)
_GRPC_POLL_STRATEGY = os.environ.get('GRPC_POLL_STRATEGY')
cdef void __prefork() nogil:
with gil:
with _fork_state.fork_in_progress_condition:
_fork_state.fork_in_progress = True
if not _fork_state.active_thread_count.await_zero_threads(
_AWAIT_THREADS_TIMEOUT_SECONDS):
_LOGGER.error(
'Failed to shutdown gRPC Python threads prior to fork. '
'Behavior after fork will be undefined.')
cdef void __postfork_parent() nogil:
with gil:
with _fork_state.fork_in_progress_condition:
_fork_state.fork_in_progress = False
_fork_state.fork_in_progress_condition.notify_all()
cdef void __postfork_child() nogil:
with gil:
# Thread could be holding the fork_in_progress_condition inside of
# block_if_fork_in_progress() when fork occurs. Reset the lock here.
_fork_state.fork_in_progress_condition = threading.Condition()
# A thread in return_from_user_request_generator() may hold this lock
# when fork occurs.
_fork_state.active_thread_count = _ActiveThreadCount()
for state_to_reset in _fork_state.postfork_states_to_reset:
state_to_reset.reset_postfork_child()
_fork_state.fork_epoch += 1
for channel in _fork_state.channels:
channel._close_on_fork()
# TODO(ericgribkoff) Check and abort if core is not shutdown
with _fork_state.fork_in_progress_condition:
_fork_state.fork_in_progress = False
def fork_handlers_and_grpc_init():
grpc_init()
if _GRPC_ENABLE_FORK_SUPPORT:
# TODO(ericgribkoff) epoll1 is default for grpcio distribution. Decide whether to expose
# grpc_get_poll_strategy_name() from ev_posix.cc to get actual polling choice.
if _GRPC_POLL_STRATEGY is not None and _GRPC_POLL_STRATEGY != "epoll1":
_LOGGER.error(
'gRPC Python fork support is only compatible with the epoll1 '
'polling engine')
return
with _fork_state.fork_handler_registered_lock:
if not _fork_state.fork_handler_registered:
pthread_atfork(&__prefork, &__postfork_parent, &__postfork_child)
_fork_state.fork_handler_registered = True
class ForkManagedThread(object):
def __init__(self, target, args=()):
if _GRPC_ENABLE_FORK_SUPPORT:
def managed_target(*args):
try:
target(*args)
finally:
_fork_state.active_thread_count.decrement()
self._thread = threading.Thread(target=managed_target, args=args)
else:
self._thread = threading.Thread(target=target, args=args)
def setDaemon(self, daemonic):
self._thread.daemon = daemonic
def start(self):
if _GRPC_ENABLE_FORK_SUPPORT:
_fork_state.active_thread_count.increment()
self._thread.start()
def join(self):
self._thread.join()
def block_if_fork_in_progress(postfork_state_to_reset=None):
if _GRPC_ENABLE_FORK_SUPPORT:
with _fork_state.fork_in_progress_condition:
if not _fork_state.fork_in_progress:
return
if postfork_state_to_reset is not None:
_fork_state.postfork_states_to_reset.append(postfork_state_to_reset)
_fork_state.active_thread_count.decrement()
_fork_state.fork_in_progress_condition.wait()
_fork_state.active_thread_count.increment()
def enter_user_request_generator():
if _GRPC_ENABLE_FORK_SUPPORT:
_fork_state.active_thread_count.decrement()
def return_from_user_request_generator():
if _GRPC_ENABLE_FORK_SUPPORT:
_fork_state.active_thread_count.increment()
block_if_fork_in_progress()
def get_fork_epoch():
return _fork_state.fork_epoch
def is_fork_support_enabled():
return _GRPC_ENABLE_FORK_SUPPORT
def fork_register_channel(channel):
if _GRPC_ENABLE_FORK_SUPPORT:
_fork_state.channels.add(channel)
def fork_unregister_channel(channel):
if _GRPC_ENABLE_FORK_SUPPORT:
_fork_state.channels.remove(channel)
class _ActiveThreadCount(object):
def __init__(self):
self._num_active_threads = 0
self._condition = threading.Condition()
def increment(self):
with self._condition:
self._num_active_threads += 1
def decrement(self):
with self._condition:
self._num_active_threads -= 1
if self._num_active_threads == 0:
self._condition.notify_all()
def await_zero_threads(self, timeout_secs):
end_time = time.time() + timeout_secs
wait_time = timeout_secs
with self._condition:
while True:
if self._num_active_threads > 0:
self._condition.wait(wait_time)
if self._num_active_threads == 0:
return True
# Thread count may have increased before this re-obtains the
# lock after a notify(). Wait again until timeout_secs has
# elapsed.
wait_time = end_time - time.time()
if wait_time <= 0:
return False
class _ForkState(object):
def __init__(self):
self.fork_in_progress_condition = threading.Condition()
self.fork_in_progress = False
self.postfork_states_to_reset = []
self.fork_handler_registered_lock = threading.Lock()
self.fork_handler_registered = False
self.active_thread_count = _ActiveThreadCount()
self.fork_epoch = 0
self.channels = set()
_fork_state = _ForkState()
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