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# -*- coding: utf-8 -*-
# daemon/
# Part of python-daemon, an implementation of PEP 3143.
# Copyright © 2009–2010 Ben Finney <>
# 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 Python Software Foundation License, version 2 or
# later as published by the Python Software Foundation.
# No warranty expressed or implied. See the file LICENSE.PSF-2 for details.
""" Daemon runner library.
import sys
import os
import signal
import errno
import pidlockfile
from daemon import DaemonContext
class DaemonRunnerError(Exception):
""" Abstract base class for errors from DaemonRunner. """
class DaemonRunnerInvalidActionError(ValueError, DaemonRunnerError):
""" Raised when specified action for DaemonRunner is invalid. """
class DaemonRunnerStartFailureError(RuntimeError, DaemonRunnerError):
""" Raised when failure starting DaemonRunner. """
class DaemonRunnerStopFailureError(RuntimeError, DaemonRunnerError):
""" Raised when failure stopping DaemonRunner. """
class DaemonRunner(object):
""" 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 ``.
* '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.
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
self.parse_args() = app
self.daemon_context = DaemonContext()
self.daemon_context.stdin = open(app.stdin_path, 'r')
self.daemon_context.stdout = open(app.stdout_path, 'w+')
self.daemon_context.stderr = open(
app.stderr_path, 'w+', buffering=0)
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 _usage_exit(self, argv):
""" Emit a usage message, then exit.
progname = os.path.basename(argv[0])
usage_exit_code = 2
action_usage = "|".join(self.action_funcs.keys())
message = "usage: %(progname)s %(action_usage)s" % vars()
def parse_args(self, argv=None):
""" Parse command-line arguments.
if argv is None:
argv = sys.argv
min_args = 2
if len(argv) < min_args:
self.action = argv[1]
if self.action not in self.action_funcs:
def _start(self):
""" Open the daemon context and run the application.
if is_pidfile_stale(self.pidfile):
except pidlockfile.AlreadyLocked:
pidfile_path = self.pidfile.path
raise DaemonRunnerStartFailureError(
"PID file %(pidfile_path)r already locked" % vars())
pid = os.getpid()
message = self.start_message % vars()
def _terminate_daemon_process(self):
""" Terminate the daemon process specified in the current PID file.
pid = self.pidfile.read_pid()
os.kill(pid, signal.SIGTERM)
except OSError, exc:
raise DaemonRunnerStopFailureError(
"Failed to terminate %(pid)d: %(exc)s" % vars())
def _stop(self):
""" Exit the daemon process specified in the current PID file.
if not self.pidfile.is_locked():
pidfile_path = self.pidfile.path
raise DaemonRunnerStopFailureError(
"PID file %(pidfile_path)r not locked" % vars())
if is_pidfile_stale(self.pidfile):
def _restart(self):
""" Stop, then start.
action_funcs = {
'start': _start,
'stop': _stop,
'restart': _restart,
def _get_action_func(self):
""" Return the function for the specified action.
Raises ``DaemonRunnerInvalidActionError`` if the action is
func = self.action_funcs[self.action]
except KeyError:
raise DaemonRunnerInvalidActionError(
"Unknown action: %(action)r" % vars(self))
return func
def do_action(self):
""" Perform the requested action.
func = self._get_action_func()
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)s\n" % vars())
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" % vars())
raise error
if not os.path.isabs(path):
error = ValueError("Not an absolute path: %(path)r" % vars())
raise error
lockfile = pidlockfile.TimeoutPIDLockFile(path, acquire_timeout)
return lockfile
def is_pidfile_stale(pidfile):
""" Determine whether a PID file is stale.
Return ``True`` (“stale”) if the contents of the PID file are
valid but do not match the PID of a currently-running process;
otherwise return ``False``.
result = False
pidfile_pid = pidfile.read_pid()
if pidfile_pid is not None:
os.kill(pidfile_pid, signal.SIG_DFL)
except OSError, exc:
if exc.errno == errno.ESRCH:
# The specified PID does not exist
result = True
return result