arbiter.py

# -*- coding: utf-8 -
#
# This file is part of gunicorn released under the MIT license.
# See the NOTICE for more information.
from __future__ import print_function

import errno
import os
import random
import select
import signal
import sys
import time

from gunicorn.errors import HaltServer, AppImportError
from gunicorn.pidfile import Pidfile
from gunicorn import sock, systemd, util

from gunicorn import __version__, SERVER_SOFTWARE


class Arbiter(object):
    """
    Arbiter maintain the workers processes alive. It launches or
    kills them if needed. It also manages application reloading
    via SIGHUP/USR2.
    """

    # A flag indicating if a worker failed to
    # to boot. If a worker process exist with
    # this error code, the arbiter will terminate.
    WORKER_BOOT_ERROR = 3

    # A flag indicating if an application failed to be loaded
    APP_LOAD_ERROR = 4

    START_CTX = {}

    LISTENERS = []
    WORKERS = {}
    PIPE = []

    # I love dynamic languages
    SIG_QUEUE = []
    SIGNALS = [getattr(signal, "SIG%s" % x)
               for x in "HUP QUIT INT TERM TTIN TTOU USR1 USR2 WINCH".split()]
    SIG_NAMES = dict(
        (getattr(signal, name), name[3:].lower()) for name in dir(signal)
        if name[:3] == "SIG" and name[3] != "_"
    )

    def __init__(self, app):
        os.environ["SERVER_SOFTWARE"] = SERVER_SOFTWARE

        self._num_workers = None
        self._last_logged_active_worker_count = None
        self.log = None

        self.setup(app)

        self.pidfile = None
        self.systemd = False
        self.worker_age = 0
        self.reexec_pid = 0
        self.master_pid = 0
        self.master_name = "Master"

        cwd = util.getcwd()

        args = sys.argv[:]
        args.insert(0, sys.executable)

        # init start context
        self.START_CTX = {
            "args": args,
            "cwd": cwd,
            0: sys.executable
        }

    def _get_num_workers(self):
        return self._num_workers

    def _set_num_workers(self, value):
        old_value = self._num_workers
        self._num_workers = value
        self.cfg.nworkers_changed(self, value, old_value)
    num_workers = property(_get_num_workers, _set_num_workers)

    def setup(self, app):
        self.app = app
        self.cfg = app.cfg

        if self.log is None:
            self.log = self.cfg.logger_class(app.cfg)

        # reopen files
        if 'GUNICORN_FD' in os.environ:
            self.log.reopen_files()

        self.worker_class = self.cfg.worker_class
        self.address = self.cfg.address
        self.num_workers = self.cfg.workers
        self.timeout = self.cfg.timeout
        self.proc_name = self.cfg.proc_name

        self.log.debug('Current configuration:\n{0}'.format(
            '\n'.join(
                '  {0}: {1}'.format(config, value.value)
                for config, value
                in sorted(self.cfg.settings.items(),
                          key=lambda setting: setting[1]))))

        # set enviroment' variables
        if self.cfg.env:
            for k, v in self.cfg.env.items():
                os.environ[k] = v

        if self.cfg.preload_app:
            self.app.wsgi()

    def start(self):
        """\
        Initialize the arbiter. Start listening and set pidfile if needed.
        """
        self.log.info("Starting gunicorn %s", __version__)

        if 'GUNICORN_PID' in os.environ:
            self.master_pid = int(os.environ.get('GUNICORN_PID'))
            self.proc_name = self.proc_name + ".2"
            self.master_name = "Master.2"

        self.pid = os.getpid()
        if self.cfg.pidfile is not None:
            pidname = self.cfg.pidfile
            if self.master_pid != 0:
                pidname += ".2"
            self.pidfile = Pidfile(pidname)
            self.pidfile.create(self.pid)
        self.cfg.on_starting(self)

        self.init_signals()

        if not self.LISTENERS:
            fds = None
            listen_fds = systemd.listen_fds()
            if listen_fds:
                self.systemd = True
                fds = range(systemd.SD_LISTEN_FDS_START,
                            systemd.SD_LISTEN_FDS_START + listen_fds)

            elif self.master_pid:
                fds = []
                for fd in os.environ.pop('GUNICORN_FD').split(','):
                    fds.append(int(fd))

            self.LISTENERS = sock.create_sockets(self.cfg, self.log, fds)

        listeners_str = ",".join([str(l) for l in self.LISTENERS])
        self.log.debug("Arbiter booted")
        self.log.info("Listening at: %s (%s)", listeners_str, self.pid)
        self.log.info("Using worker: %s", self.cfg.worker_class_str)

        # check worker class requirements
        if hasattr(self.worker_class, "check_config"):
            self.worker_class.check_config(self.cfg, self.log)

        self.cfg.when_ready(self)

    def init_signals(self):
        """\
        Initialize master signal handling. Most of the signals
        are queued. Child signals only wake up the master.
        """
        # close old PIPE
        for p in self.PIPE:
            os.close(p)

        # initialize the pipe
        self.PIPE = pair = os.pipe()
        for p in pair:
            util.set_non_blocking(p)
            util.close_on_exec(p)

        self.log.close_on_exec()

        # initialize all signals
        for s in self.SIGNALS:
            signal.signal(s, self.signal)
        signal.signal(signal.SIGCHLD, self.handle_chld)

    def signal(self, sig, frame):
        if len(self.SIG_QUEUE) < 5:
            self.SIG_QUEUE.append(sig)
            self.wakeup()

    def run(self):
        "Main master loop."
        self.start()
        util._setproctitle("master [%s]" % self.proc_name)

        try:
            self.manage_workers()

            while True:
                self.maybe_promote_master()

                sig = self.SIG_QUEUE.pop(0) if self.SIG_QUEUE else None
                if sig is None:
                    self.sleep()
                    self.murder_workers()
                    self.manage_workers()
                    continue

                if sig not in self.SIG_NAMES:
                    self.log.info("Ignoring unknown signal: %s", sig)
                    continue

                signame = self.SIG_NAMES.get(sig)
                handler = getattr(self, "handle_%s" % signame, None)
                if not handler:
                    self.log.error("Unhandled signal: %s", signame)
                    continue
                self.log.info("Handling signal: %s", signame)
                handler()
                self.wakeup()
        except StopIteration:
            self.halt()
        except KeyboardInterrupt:
            self.halt()
        except HaltServer as inst:
            self.halt(reason=inst.reason, exit_status=inst.exit_status)
        except SystemExit:
            raise
        except Exception:
            self.log.info("Unhandled exception in main loop",
                          exc_info=True)
            self.stop(False)
            if self.pidfile is not None:
                self.pidfile.unlink()
            sys.exit(-1)

    def handle_chld(self, sig, frame):
        "SIGCHLD handling"
        self.reap_workers()
        self.wakeup()

    def handle_hup(self):
        """\
        HUP handling.
        - Reload configuration
        - Start the new worker processes with a new configuration
        - Gracefully shutdown the old worker processes
        """
        self.log.info("Hang up: %s", self.master_name)
        self.reload()

    def handle_term(self):
        "SIGTERM handling"
        raise StopIteration

    def handle_int(self):
        "SIGINT handling"
        self.stop(False)
        raise StopIteration

    def handle_quit(self):
        "SIGQUIT handling"
        self.stop(False)
        raise StopIteration

    def handle_ttin(self):
        """\
        SIGTTIN handling.
        Increases the number of workers by one.
        """
        self.num_workers += 1
        self.manage_workers()

    def handle_ttou(self):
        """\
        SIGTTOU handling.
        Decreases the number of workers by one.
        """
        if self.num_workers <= 1:
            return
        self.num_workers -= 1
        self.manage_workers()

    def handle_usr1(self):
        """\
        SIGUSR1 handling.
        Kill all workers by sending them a SIGUSR1
        """
        self.log.reopen_files()
        self.kill_workers(signal.SIGUSR1)

    def handle_usr2(self):
        """\
        SIGUSR2 handling.
        Creates a new master/worker set as a slave of the current
        master without affecting old workers. Use this to do live
        deployment with the ability to backout a change.
        """
        self.reexec()

    def handle_winch(self):
        """SIGWINCH handling"""
        if self.cfg.daemon:
            self.log.info("graceful stop of workers")
            self.num_workers = 0
            self.kill_workers(signal.SIGTERM)
        else:
            self.log.debug("SIGWINCH ignored. Not daemonized")

    def maybe_promote_master(self):
        if self.master_pid == 0:
            return

        if self.master_pid != os.getppid():
            self.log.info("Master has been promoted.")
            # reset master infos
            self.master_name = "Master"
            self.master_pid = 0
            self.proc_name = self.cfg.proc_name
            del os.environ['GUNICORN_PID']
            # rename the pidfile
            if self.pidfile is not None:
                self.pidfile.rename(self.cfg.pidfile)
            # reset proctitle
            util._setproctitle("master [%s]" % self.proc_name)

    def wakeup(self):
        """\
        Wake up the arbiter by writing to the PIPE
        """
        try:
            os.write(self.PIPE[1], b'.')
        except IOError as e:
            if e.errno not in [errno.EAGAIN, errno.EINTR]:
                raise

    def halt(self, reason=None, exit_status=0):
        """ halt arbiter """
        self.stop()
        self.log.info("Shutting down: %s", self.master_name)
        if reason is not None:
            self.log.info("Reason: %s", reason)
        if self.pidfile is not None:
            self.pidfile.unlink()
        self.cfg.on_exit(self)
        sys.exit(exit_status)

    def sleep(self):
        """\
        Sleep until PIPE is readable or we timeout.
        A readable PIPE means a signal occurred.
        """
        try:
            ready = select.select([self.PIPE[0]], [], [], 1.0)
            if not ready[0]:
                return
            while os.read(self.PIPE[0], 1):
                pass
        except (select.error, OSError) as e:
            # TODO: select.error is a subclass of OSError since Python 3.3.
            error_number = getattr(e, 'errno', e.args[0])
            if error_number not in [errno.EAGAIN, errno.EINTR]:
                raise
        except KeyboardInterrupt:
            sys.exit()

    def stop(self, graceful=True):
        """\
        Stop workers

        :attr graceful: boolean, If True (the default) workers will be
        killed gracefully  (ie. trying to wait for the current connection)
        """

        unlink = self.reexec_pid == self.master_pid == 0 and not self.systemd
        sock.close_sockets(self.LISTENERS, unlink)

        self.LISTENERS = []
        sig = signal.SIGTERM
        if not graceful:
            sig = signal.SIGQUIT
        limit = time.time() + self.cfg.graceful_timeout
        # instruct the workers to exit
        self.kill_workers(sig)
        # wait until the graceful timeout
        while self.WORKERS and time.time() < limit:
            time.sleep(0.1)

        self.kill_workers(signal.SIGKILL)

    def reexec(self):
        """\
        Relaunch the master and workers.
        """
        if self.reexec_pid != 0:
            self.log.warning("USR2 signal ignored. Child exists.")
            return

        if self.master_pid != 0:
            self.log.warning("USR2 signal ignored. Parent exists.")
            return

        master_pid = os.getpid()
        self.reexec_pid = os.fork()
        if self.reexec_pid != 0:
            return

        self.cfg.pre_exec(self)

        environ = self.cfg.env_orig.copy()
        environ['GUNICORN_PID'] = str(master_pid)

        if self.systemd:
            environ['LISTEN_PID'] = str(os.getpid())
            environ['LISTEN_FDS'] = str(len(self.LISTENERS))
        else:
            environ['GUNICORN_FD'] = ','.join(
                str(l.fileno()) for l in self.LISTENERS)

        os.chdir(self.START_CTX['cwd'])

        # exec the process using the original environment
        os.execvpe(self.START_CTX[0], self.START_CTX['args'], environ)

    def reload(self):
        old_address = self.cfg.address

        # reset old environment
        for k in self.cfg.env:
            if k in self.cfg.env_orig:
                # reset the key to the value it had before
                # we launched gunicorn
                os.environ[k] = self.cfg.env_orig[k]
            else:
                # delete the value set by gunicorn
                try:
                    del os.environ[k]
                except KeyError:
                    pass

        # reload conf
        self.app.reload()
        self.setup(self.app)

        # reopen log files
        self.log.reopen_files()

        # do we need to change listener ?
        if old_address != self.cfg.address:
            # close all listeners
            for l in self.LISTENERS:
                l.close()
            # init new listeners
            self.LISTENERS = sock.create_sockets(self.cfg, self.log)
            listeners_str = ",".join([str(l) for l in self.LISTENERS])
            self.log.info("Listening at: %s", listeners_str)

        # do some actions on reload
        self.cfg.on_reload(self)

        # unlink pidfile
        if self.pidfile is not None:
            self.pidfile.unlink()

        # create new pidfile
        if self.cfg.pidfile is not None:
            self.pidfile = Pidfile(self.cfg.pidfile)
            self.pidfile.create(self.pid)

        # set new proc_name
        util._setproctitle("master [%s]" % self.proc_name)

        # spawn new workers
        for _ in range(self.cfg.workers):
            self.spawn_worker()

        # manage workers
        self.manage_workers()

    def murder_workers(self):
        """\
        Kill unused/idle workers
        """
        if not self.timeout:
            return
        workers = list(self.WORKERS.items())
        for (pid, worker) in workers:
            try:
                if time.time() - worker.tmp.last_update() <= self.timeout:
                    continue
            except (OSError, ValueError):
                continue

            if not worker.aborted:
                self.log.critical("WORKER TIMEOUT (pid:%s)", pid)
                worker.aborted = True
                self.kill_worker(pid, signal.SIGABRT)
            else:
                self.kill_worker(pid, signal.SIGKILL)

    def reap_workers(self):
        """\
        Reap workers to avoid zombie processes
        """
        try:
            while True:
                wpid, status = os.waitpid(-1, os.WNOHANG)
                if not wpid:
                    break
                if self.reexec_pid == wpid:
                    self.reexec_pid = 0
                else:
                    # A worker was terminated. If the termination reason was
                    # that it could not boot, we'll shut it down to avoid
                    # infinite start/stop cycles.
                    exitcode = status >> 8
                    if exitcode == self.WORKER_BOOT_ERROR:
                        reason = "Worker failed to boot."
                        raise HaltServer(reason, self.WORKER_BOOT_ERROR)
                    if exitcode == self.APP_LOAD_ERROR:
                        reason = "App failed to load."
                        raise HaltServer(reason, self.APP_LOAD_ERROR)

                    worker = self.WORKERS.pop(wpid, None)
                    if not worker:
                        continue
                    worker.tmp.close()
                    self.cfg.child_exit(self, worker)
        except OSError as e:
            if e.errno != errno.ECHILD:
                raise

    def manage_workers(self):
        """\
        Maintain the number of workers by spawning or killing
        as required.
        """
        if len(self.WORKERS.keys()) < self.num_workers:
            self.spawn_workers()

        workers = self.WORKERS.items()
        workers = sorted(workers, key=lambda w: w[1].age)
        while len(workers) > self.num_workers:
            (pid, _) = workers.pop(0)
            self.kill_worker(pid, signal.SIGTERM)

        active_worker_count = len(workers)
        if self._last_logged_active_worker_count != active_worker_count:
            self._last_logged_active_worker_count = active_worker_count
            self.log.debug("{0} workers".format(active_worker_count),
                           extra={"metric": "gunicorn.workers",
                                  "value": active_worker_count,
                                  "mtype": "gauge"})

    def spawn_worker(self):
        self.worker_age += 1
        worker = self.worker_class(self.worker_age, self.pid, self.LISTENERS,
                                   self.app, self.timeout / 2.0,
                                   self.cfg, self.log)
        self.cfg.pre_fork(self, worker)
        pid = os.fork()
        if pid != 0:
            worker.pid = pid
            self.WORKERS[pid] = worker
            return pid

        # Do not inherit the temporary files of other workers
        for sibling in self.WORKERS.values():
            sibling.tmp.close()
        
        # Process Child
        worker.pid = os.getpid()
        try:
            util._setproctitle("worker [%s]" % self.proc_name)
            self.log.info("Booting worker with pid: %s", worker.pid)
            self.cfg.post_fork(self, worker)
            worker.init_process()
            sys.exit(0)
        except SystemExit:
            raise
        except AppImportError as e:
            self.log.debug("Exception while loading the application",
                           exc_info=True)
            print("%s" % e, file=sys.stderr)
            sys.stderr.flush()
            sys.exit(self.APP_LOAD_ERROR)
        except Exception as e:
            self.log.exception("Exception in worker process", exc_info=e)
            if not worker.booted:
                sys.exit(self.WORKER_BOOT_ERROR)
            sys.exit(-1)
        finally:
            self.log.info("Worker exiting (pid: %s)", worker.pid)
            try:
                worker.tmp.close()
                self.cfg.worker_exit(self, worker)
            except Exception as e:
                self.log.warning("Exception during worker exit", exc_info=e)

    def spawn_workers(self):
        """\
        Spawn new workers as needed.

        This is where a worker process leaves the main loop
        of the master process.
        """

        for _ in range(self.num_workers - len(self.WORKERS.keys())):
            self.spawn_worker()
            time.sleep(0.1 * random.random())

    def kill_workers(self, sig):
        """\
        Kill all workers with the signal `sig`
        :attr sig: `signal.SIG*` value
        """
        worker_pids = list(self.WORKERS.keys())
        for pid in worker_pids:
            self.kill_worker(pid, sig)

    def kill_worker(self, pid, sig):
        """\
        Kill a worker

        :attr pid: int, worker pid
        :attr sig: `signal.SIG*` value
         """
        try:
            os.kill(pid, sig)
        except OSError as e:
            if e.errno == errno.ESRCH:
                try:
                    worker = self.WORKERS.pop(pid)
                    worker.tmp.close()
                    self.cfg.worker_exit(self, worker)
                    return
                except (KeyError, OSError):
                    return
            raise