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# Copyright 2019-present MongoDB, Inc.
#
# 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.
"""Support for spawning a daemon process.
PyMongo only attempts to spawn the mongocryptd daemon process when automatic
client-side field level encryption is enabled. See
:ref:`automatic-client-side-encryption` for more info.
"""
import os
import subprocess
import sys
import time
# The maximum amount of time to wait for the intermediate subprocess.
_WAIT_TIMEOUT = 10
_THIS_FILE = os.path.realpath(__file__)
if sys.version_info[0] < 3:
def _popen_wait(popen, timeout):
"""Implement wait timeout support for Python 2."""
from pymongo.monotonic import time as _time
deadline = _time() + timeout
# Initial delay of 1ms
delay = .0005
while True:
returncode = popen.poll()
if returncode is not None:
return returncode
remaining = deadline - _time()
if remaining <= 0:
# Just return None instead of raising an error.
return None
delay = min(delay * 2, remaining, .5)
time.sleep(delay)
else:
def _popen_wait(popen, timeout):
"""Implement wait timeout support for Python 3."""
try:
return popen.wait(timeout=timeout)
except subprocess.TimeoutExpired:
# Silence TimeoutExpired errors.
return None
def _silence_resource_warning(popen):
"""Silence Popen's ResourceWarning.
Note this should only be used if the process was created as a daemon.
"""
# Set the returncode to avoid this warning when popen is garbage collected:
# "ResourceWarning: subprocess XXX is still running".
# See https://bugs.python.org/issue38890 and
# https://bugs.python.org/issue26741.
popen.returncode = 0
if sys.platform == 'win32':
# On Windows we spawn the daemon process simply by using DETACHED_PROCESS.
_DETACHED_PROCESS = getattr(subprocess, 'DETACHED_PROCESS', 0x00000008)
def _spawn_daemon(args):
"""Spawn a daemon process (Windows)."""
with open(os.devnull, 'r+b') as devnull:
popen = subprocess.Popen(
args,
creationflags=_DETACHED_PROCESS,
stdin=devnull, stderr=devnull, stdout=devnull)
_silence_resource_warning(popen)
else:
# On Unix we spawn the daemon process with a double Popen.
# 1) The first Popen runs this file as a Python script using the current
# interpreter.
# 2) The script then decouples itself and performs the second Popen to
# spawn the daemon process.
# 3) The original process waits up to 10 seconds for the script to exit.
#
# Note that we do not call fork() directly because we want this procedure
# to be safe to call from any thread. Using Popen instead of fork also
# avoids triggering the application's os.register_at_fork() callbacks when
# we spawn the mongocryptd daemon process.
def _spawn(args):
"""Spawn the process and silence stdout/stderr."""
with open(os.devnull, 'r+b') as devnull:
return subprocess.Popen(
args,
close_fds=True,
stdin=devnull, stderr=devnull, stdout=devnull)
def _spawn_daemon_double_popen(args):
"""Spawn a daemon process using a double subprocess.Popen."""
spawner_args = [sys.executable, _THIS_FILE]
spawner_args.extend(args)
temp_proc = subprocess.Popen(spawner_args, close_fds=True)
# Reap the intermediate child process to avoid creating zombie
# processes.
_popen_wait(temp_proc, _WAIT_TIMEOUT)
def _spawn_daemon(args):
"""Spawn a daemon process (Unix)."""
# "If Python is unable to retrieve the real path to its executable,
# sys.executable will be an empty string or None".
if sys.executable:
_spawn_daemon_double_popen(args)
else:
# Fallback to spawn a non-daemon process without silencing the
# resource warning. We do not use fork here because it is not
# safe to call from a thread on all systems.
# Unfortunately, this means that:
# 1) If the parent application is killed via Ctrl-C, the
# non-daemon process will also be killed.
# 2) Each non-daemon process will hang around as a zombie process
# until the main application exits.
_spawn(args)
if __name__ == '__main__':
# Attempt to start a new session to decouple from the parent.
if hasattr(os, 'setsid'):
try:
os.setsid()
except OSError:
pass
# We are performing a double fork (Popen) to spawn the process as a
# daemon so it is safe to ignore the resource warning.
_silence_resource_warning(_spawn(sys.argv[1:]))
os._exit(0)