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author | Richard van der Hoff <1389908+richvdh@users.noreply.github.com> | 2020-08-04 10:03:41 +0100 |
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committer | GitHub <noreply@github.com> | 2020-08-04 10:03:41 +0100 |
commit | 916cf2d439c406dd08310714ae31216608ea6fa6 (patch) | |
tree | 1b7207659c07dfe86483b22abd305b5f32e9cb14 /synapse/util | |
parent | Remove signature check on v1 identity server lookups (#8001) (diff) | |
download | synapse-916cf2d439c406dd08310714ae31216608ea6fa6.tar.xz |
re-implement daemonize (#8011)
This has long been something I've wanted to do. Basically the `Daemonize` code is both too flexible and not flexible enough, in that it offers a bunch of features that we don't use (changing UID, closing FDs in the child, logging to syslog) and doesn't offer a bunch that we could do with (redirecting stdout/err to a file instead of /dev/null; having the parent not exit until the child is running). As a first step, I've lifted the Daemonize code and removed the bits we don't use. This should be a non-functional change. Fixing everything else will come later.
Diffstat (limited to '')
-rw-r--r-- | synapse/util/daemonize.py | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/synapse/util/daemonize.py b/synapse/util/daemonize.py new file mode 100644 index 0000000000..a7913fa1af --- /dev/null +++ b/synapse/util/daemonize.py @@ -0,0 +1,131 @@ +# -*- coding: utf-8 -*- +# Copyright (c) 2012, 2013, 2014 Ilya Otyutskiy <ilya.otyutskiy@icloud.com> +# Copyright 2020 The Matrix.org Foundation C.I.C. +# +# 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 atexit +import fcntl +import logging +import os +import signal +import sys + + +def daemonize_process(pid_file: str, logger: logging.Logger, chdir: str = "/") -> None: + """daemonize the current process + + This calls fork(), and has the main process exit. When it returns we will be + running in the child process. + """ + + # If pidfile already exists, we should read pid from there; to overwrite it, if + # locking will fail, because locking attempt somehow purges the file contents. + if os.path.isfile(pid_file): + with open(pid_file, "r") as pid_fh: + old_pid = pid_fh.read() + + # Create a lockfile so that only one instance of this daemon is running at any time. + try: + lock_fh = open(pid_file, "w") + except IOError: + print("Unable to create the pidfile.") + sys.exit(1) + + try: + # Try to get an exclusive lock on the file. This will fail if another process + # has the file locked. + fcntl.flock(lock_fh, fcntl.LOCK_EX | fcntl.LOCK_NB) + except IOError: + print("Unable to lock on the pidfile.") + # We need to overwrite the pidfile if we got here. + # + # XXX better to avoid overwriting it, surely. this looks racey as the pid file + # could be created between us trying to read it and us trying to lock it. + with open(pid_file, "w") as pid_fh: + pid_fh.write(old_pid) + sys.exit(1) + + # Fork, creating a new process for the child. + process_id = os.fork() + + if process_id != 0: + # parent process + sys.exit(0) + + # This is the child process. Continue. + + # Stop listening for signals that the parent process receives. + # This is done by getting a new process id. + # setpgrp() is an alternative to setsid(). + # setsid puts the process in a new parent group and detaches its controlling + # terminal. + + os.setsid() + + # point stdin, stdout, stderr at /dev/null + devnull = "/dev/null" + if hasattr(os, "devnull"): + # Python has set os.devnull on this system, use it instead as it might be + # different than /dev/null. + devnull = os.devnull + + devnull_fd = os.open(devnull, os.O_RDWR) + os.dup2(devnull_fd, 0) + os.dup2(devnull_fd, 1) + os.dup2(devnull_fd, 2) + os.close(devnull_fd) + + # now that we have redirected stderr to /dev/null, any uncaught exceptions will + # get sent to /dev/null, so make sure we log them. + # + # (we don't normally expect reactor.run to raise any exceptions, but this will + # also catch any other uncaught exceptions before we get that far.) + + def excepthook(type_, value, traceback): + logger.critical("Unhanded exception", exc_info=(type_, value, traceback)) + + sys.excepthook = excepthook + + # Set umask to default to safe file permissions when running as a root daemon. 027 + # is an octal number which we are typing as 0o27 for Python3 compatibility. + os.umask(0o27) + + # Change to a known directory. If this isn't done, starting a daemon in a + # subdirectory that needs to be deleted results in "directory busy" errors. + os.chdir(chdir) + + try: + lock_fh.write("%s" % (os.getpid())) + lock_fh.flush() + except IOError: + logger.error("Unable to write pid to the pidfile.") + print("Unable to write pid to the pidfile.") + sys.exit(1) + + # write a log line on SIGTERM. + def sigterm(signum, frame): + logger.warning("Caught signal %s. Stopping daemon." % signum) + sys.exit(0) + + signal.signal(signal.SIGTERM, sigterm) + + # Cleanup pid file at exit. + def exit(): + logger.warning("Stopping daemon.") + os.remove(pid_file) + sys.exit(0) + + atexit.register(exit) + + logger.warning("Starting daemon.") |