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runner.py
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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 :