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+# -*- coding: utf-8 -*-
+
+# daemon/runner.py
+# Part of ‘python-daemon’, an implementation of PEP 3143.
+#
+# Copyright © 2009–2015 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.
+
+""" Daemon runner library.
+ """
+
+from __future__ import (absolute_import, unicode_literals)
+
+import sys
+import os
+import signal
+import errno
+try:
+ # Python 3 standard library.
+ ProcessLookupError
+except NameError:
+ # No such class in Python 2.
+ ProcessLookupError = NotImplemented
+
+import lockfile
+
+from . import pidfile
+from .daemon import (basestring, unicode)
+from .daemon import DaemonContext
+from .daemon import _chain_exception_from_existing_exception_context
+
+
+class DaemonRunnerError(Exception):
+ """ Abstract base class for errors from DaemonRunner. """
+
+ def __init__(self, *args, **kwargs):
+ self._chain_from_context()
+
+ super(DaemonRunnerError, self).__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.
+
+ """
+
+ __metaclass__ = type
+
+ 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.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)
+
+ 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.
+
+ :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
+
+
+# Local variables:
+# coding: utf-8
+# mode: python
+# End:
+# vim: fileencoding=utf-8 filetype=python :