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# -*- coding: utf-8 -*-
# daemon/runner.py
# Part of ‘python-daemon’, an implementation of PEP 3143.
#
# This is free software, and you are welcome to redistribute it under
# certain conditions; see the end of this file for copyright
# information, grant of license, and disclaimer of warranty.
""" Daemon runner library.
"""
from __future__ import (absolute_import, unicode_literals)
import errno
import os
import signal
import sys
import warnings
import lockfile
from . import pidfile
from .daemon import (
_chain_exception_from_existing_exception_context,
DaemonContext,
basestring,
unicode,
)
try:
# Python 3 standard library.
ProcessLookupError
except NameError:
# No such class in Python 2.
ProcessLookupError = NotImplemented
__metaclass__ = type
warnings.warn(
"The ‘runner’ module is not a supported API for this library.",
DeprecationWarning)
class DaemonRunnerError(Exception):
""" Abstract base class for errors from DaemonRunner. """
def __init__(self, *args, **kwargs):
self._chain_from_context()
super().__init__(*args, **kwargs)
def _chain_from_context(self):
_chain_exception_from_existing_exception_context(self, as_cause=True)
class DaemonRunnerInvalidActionError(DaemonRunnerError, ValueError):
""" Raised when specified action for DaemonRunner is invalid. """
def _chain_from_context(self):
# This exception is normally not caused by another.
_chain_exception_from_existing_exception_context(self, as_cause=False)
class DaemonRunnerStartFailureError(DaemonRunnerError, RuntimeError):
""" Raised when failure starting DaemonRunner. """
class DaemonRunnerStopFailureError(DaemonRunnerError, RuntimeError):
""" Raised when failure stopping DaemonRunner. """
class DaemonRunner:
""" Controller for a callable running in a separate background process.
The first command-line argument is the action to take:
* 'start': Become a daemon and call `app.run()`.
* 'stop': Exit the daemon process specified in the PID file.
* 'restart': Stop, then start.
"""
start_message = "started with pid {pid:d}"
def __init__(self, app):
""" Set up the parameters of a new runner.
:param app: The application instance; see below.
:return: ``None``.
The `app` argument must have the following attributes:
* `stdin_path`, `stdout_path`, `stderr_path`: Filesystem paths
to open and replace the existing `sys.stdin`, `sys.stdout`,
`sys.stderr`.
* `pidfile_path`: Absolute filesystem path to a file that will
be used as the PID file for the daemon. If ``None``, no PID
file will be used.
* `pidfile_timeout`: Used as the default acquisition timeout
value supplied to the runner's PID lock file.
* `run`: Callable that will be invoked when the daemon is
started.
"""
self.parse_args()
self.app = app
self.daemon_context = DaemonContext()
self._open_streams_from_app_stream_paths(app)
self.pidfile = None
if app.pidfile_path is not None:
self.pidfile = make_pidlockfile(
app.pidfile_path, app.pidfile_timeout)
self.daemon_context.pidfile = self.pidfile
def _open_streams_from_app_stream_paths(self, app):
""" Open the `daemon_context` streams from the paths specified.
:param app: The application instance.
Open the `daemon_context` standard streams (`stdin`,
`stdout`, `stderr`) as stream objects of the appropriate
types, from each of the corresponding filesystem paths
from the `app`.
"""
self.daemon_context.stdin = open(app.stdin_path, 'rt')
self.daemon_context.stdout = open(app.stdout_path, 'w+t')
self.daemon_context.stderr = open(
app.stderr_path, 'w+t', buffering=0)
def _usage_exit(self, argv):
""" Emit a usage message, then exit.
:param argv: The command-line arguments used to invoke the
program, as a sequence of strings.
:return: ``None``.
"""
progname = os.path.basename(argv[0])
usage_exit_code = 2
action_usage = "|".join(self.action_funcs.keys())
message = "usage: {progname} {usage}".format(
progname=progname, usage=action_usage)
emit_message(message)
sys.exit(usage_exit_code)
def parse_args(self, argv=None):
""" Parse command-line arguments.
:param argv: The command-line arguments used to invoke the
program, as a sequence of strings.
:return: ``None``.
The parser expects the first argument as the program name, the
second argument as the action to perform.
If the parser fails to parse the arguments, emit a usage
message and exit the program.
"""
if argv is None:
argv = sys.argv
min_args = 2
if len(argv) < min_args:
self._usage_exit(argv)
self.action = unicode(argv[1])
if self.action not in self.action_funcs:
self._usage_exit(argv)
def _start(self):
""" Open the daemon context and run the application.
:return: ``None``.
:raises DaemonRunnerStartFailureError: If the PID file cannot
be locked by this process.
"""
if is_pidfile_stale(self.pidfile):
self.pidfile.break_lock()
try:
self.daemon_context.open()
except lockfile.AlreadyLocked:
error = DaemonRunnerStartFailureError(
"PID file {pidfile.path!r} already locked".format(
pidfile=self.pidfile))
raise error
pid = os.getpid()
message = self.start_message.format(pid=pid)
emit_message(message)
self.app.run()
def _terminate_daemon_process(self):
""" Terminate the daemon process specified in the current PID file.
:return: ``None``.
:raises DaemonRunnerStopFailureError: If terminating the daemon
fails with an OS error.
"""
pid = self.pidfile.read_pid()
try:
os.kill(pid, signal.SIGTERM)
except OSError as exc:
error = DaemonRunnerStopFailureError(
"Failed to terminate {pid:d}: {exc}".format(
pid=pid, exc=exc))
raise error
def _stop(self):
""" Exit the daemon process specified in the current PID file.
:return: ``None``.
:raises DaemonRunnerStopFailureError: If the PID file is not
already locked.
"""
if not self.pidfile.is_locked():
error = DaemonRunnerStopFailureError(
"PID file {pidfile.path!r} not locked".format(
pidfile=self.pidfile))
raise error
if is_pidfile_stale(self.pidfile):
self.pidfile.break_lock()
else:
self._terminate_daemon_process()
def _restart(self):
""" Stop, then start.
"""
self._stop()
self._start()
action_funcs = {
'start': _start,
'stop': _stop,
'restart': _restart,
}
def _get_action_func(self):
""" Get the function for the specified action.
:return: The function object corresponding to the specified
action.
:raises DaemonRunnerInvalidActionError: if the action is
unknown.
The action is specified by the `action` attribute, which is set
during `parse_args`.
"""
try:
func = self.action_funcs[self.action]
except KeyError:
error = DaemonRunnerInvalidActionError(
"Unknown action: {action!r}".format(
action=self.action))
raise error
return func
def do_action(self):
""" Perform the requested action.
:return: ``None``.
The action is specified by the `action` attribute, which is set
during `parse_args`.
"""
func = self._get_action_func()
func(self)
def emit_message(message, stream=None):
""" Emit a message to the specified stream (default `sys.stderr`). """
if stream is None:
stream = sys.stderr
stream.write("{message}\n".format(message=message))
stream.flush()
def make_pidlockfile(path, acquire_timeout):
""" Make a PIDLockFile instance with the given filesystem path. """
if not isinstance(path, basestring):
error = ValueError("Not a filesystem path: {path!r}".format(
path=path))
raise error
if not os.path.isabs(path):
error = ValueError("Not an absolute path: {path!r}".format(
path=path))
raise error
lockfile = pidfile.TimeoutPIDLockFile(path, acquire_timeout)
return lockfile
def is_pidfile_stale(pidfile):
""" Determine whether a PID file is stale.
:return: ``True`` iff the PID file is stale; otherwise ``False``.
The PID file is “stale” if its contents are valid but do not
match the PID of a currently-running process.
"""
result = False
pidfile_pid = pidfile.read_pid()
if pidfile_pid is not None:
try:
os.kill(pidfile_pid, signal.SIG_DFL)
except ProcessLookupError:
# The specified PID does not exist.
result = True
except OSError as exc:
if exc.errno == errno.ESRCH:
# Under Python 2, process lookup error is an OSError.
# The specified PID does not exist.
result = True
return result
# Copyright © 2009–2019 Ben Finney <ben+python@benfinney.id.au>
# Copyright © 2007–2008 Robert Niederreiter, Jens Klein
# Copyright © 2003 Clark Evans
# Copyright © 2002 Noah Spurrier
# Copyright © 2001 Jürgen Hermann
#
# This is free software: you may copy, modify, and/or distribute this work
# under the terms of the Apache License, version 2.0 as published by the
# Apache Software Foundation.
# No warranty expressed or implied. See the file ‘LICENSE.ASF-2’ for details.
# Local variables:
# coding: utf-8
# mode: python
# End:
# vim: fileencoding=utf-8 filetype=python :
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