libevreactor.py

# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import atexit
from collections import deque
from functools import partial
import logging
import os
import socket
import ssl
from threading import Lock, Thread
import time

from cassandra import DependencyException
try:
    import cassandra.io.libevwrapper as libev
except ImportError:
    raise DependencyException(
        "The C extension needed to use libev was not found.  This "
        "probably means that you didn't have the required build dependencies "
        "when installing the driver.  See "
        "https://docs.datastax.com/en/developer/python-driver/latest/installation/index.html#c-extensions "
        "for instructions on installing build dependencies and building "
        "the C extension.")

from cassandra.connection import (Connection, ConnectionShutdown,
                                  NONBLOCKING, Timer, TimerManager)


log = logging.getLogger(__name__)


def _cleanup(loop):
    if loop:
        loop._cleanup()


class LibevLoop(object):

    def __init__(self):
        self._pid = os.getpid()
        self._loop = libev.Loop()
        self._notifier = libev.Async(self._loop)
        self._notifier.start()

        # prevent _notifier from keeping the loop from returning
        self._loop.unref()

        self._started = False
        self._shutdown = False
        self._lock = Lock()
        self._lock_thread = Lock()

        self._thread = None

        # set of all connections; only replaced with a new copy
        # while holding _conn_set_lock, never modified in place
        self._live_conns = set()
        # newly created connections that need their write/read watcher started
        self._new_conns = set()
        # recently closed connections that need their write/read watcher stopped
        self._closed_conns = set()
        self._conn_set_lock = Lock()

        self._preparer = libev.Prepare(self._loop, self._loop_will_run)
        # prevent _preparer from keeping the loop from returning
        self._loop.unref()
        self._preparer.start()

        self._timers = TimerManager()
        self._loop_timer = libev.Timer(self._loop, self._on_loop_timer)

    def maybe_start(self):
        should_start = False
        with self._lock:
            if not self._started:
                log.debug("Starting libev event loop")
                self._started = True
                should_start = True

        if should_start:
            with self._lock_thread:
                if not self._shutdown:
                    self._thread = Thread(target=self._run_loop, name="event_loop")
                    self._thread.daemon = True
                    self._thread.start()

        self._notifier.send()

    def _run_loop(self):
        while True:
            self._loop.start()
            # there are still active watchers, no deadlock
            with self._lock:
                if not self._shutdown and self._live_conns:
                    log.debug("Restarting event loop")
                    continue
                else:
                    # all Connections have been closed, no active watchers
                    log.debug("All Connections currently closed, event loop ended")
                    self._started = False
                    break

    def _cleanup(self):
        self._shutdown = True
        if not self._thread:
            return

        for conn in self._live_conns | self._new_conns | self._closed_conns:
            conn.close()
            for watcher in (conn._write_watcher, conn._read_watcher):
                if watcher:
                    watcher.stop()

        self.notify()  # wake the timer watcher

        # PYTHON-752 Thread might have just been created and not started
        with self._lock_thread:
            self._thread.join(timeout=1.0)

        if self._thread.is_alive():
            log.warning(
                "Event loop thread could not be joined, so shutdown may not be clean. "
                "Please call Cluster.shutdown() to avoid this.")

        log.debug("Event loop thread was joined")

    def add_timer(self, timer):
        self._timers.add_timer(timer)
        self._notifier.send()  # wake up in case this timer is earlier

    def _update_timer(self):
        if not self._shutdown:
            next_end = self._timers.service_timeouts()
            if next_end:
                self._loop_timer.start(next_end - time.time())  # timer handles negative values
        else:
            self._loop_timer.stop()

    def _on_loop_timer(self):
        self._timers.service_timeouts()

    def notify(self):
        self._notifier.send()

    def connection_created(self, conn):
        with self._conn_set_lock:
            new_live_conns = self._live_conns.copy()
            new_live_conns.add(conn)
            self._live_conns = new_live_conns

            new_new_conns = self._new_conns.copy()
            new_new_conns.add(conn)
            self._new_conns = new_new_conns

    def connection_destroyed(self, conn):
        with self._conn_set_lock:
            new_live_conns = self._live_conns.copy()
            new_live_conns.discard(conn)
            self._live_conns = new_live_conns

            new_closed_conns = self._closed_conns.copy()
            new_closed_conns.add(conn)
            self._closed_conns = new_closed_conns

        self._notifier.send()

    def _loop_will_run(self, prepare):
        changed = False
        for conn in self._live_conns:
            if not conn.deque and conn._write_watcher_is_active:
                if conn._write_watcher:
                    conn._write_watcher.stop()
                conn._write_watcher_is_active = False
                changed = True
            elif conn.deque and not conn._write_watcher_is_active:
                conn._write_watcher.start()
                conn._write_watcher_is_active = True
                changed = True

        if self._new_conns:
            with self._conn_set_lock:
                to_start = self._new_conns
                self._new_conns = set()

            for conn in to_start:
                conn._read_watcher.start()

            changed = True

        if self._closed_conns:
            with self._conn_set_lock:
                to_stop = self._closed_conns
                self._closed_conns = set()

            for conn in to_stop:
                if conn._write_watcher:
                    conn._write_watcher.stop()
                    # clear reference cycles from IO callback
                    del conn._write_watcher
                if conn._read_watcher:
                    conn._read_watcher.stop()
                    # clear reference cycles from IO callback
                    del conn._read_watcher

            changed = True

        # TODO: update to do connection management, timer updates through dedicated async 'notifier' callbacks
        self._update_timer()

        if changed:
            self._notifier.send()


_global_loop = None
atexit.register(lambda: _cleanup(_global_loop))


class LibevConnection(Connection):
    """
    An implementation of :class:`.Connection` that uses libev for its event loop.
    """
    _write_watcher_is_active = False
    _read_watcher = None
    _write_watcher = None
    _socket = None

    @classmethod
    def initialize_reactor(cls):
        global _global_loop
        if not _global_loop:
            _global_loop = LibevLoop()
        else:
            if _global_loop._pid != os.getpid():
                log.debug("Detected fork, clearing and reinitializing reactor state")
                cls.handle_fork()
                _global_loop = LibevLoop()

    @classmethod
    def handle_fork(cls):
        global _global_loop
        if _global_loop:
            _global_loop._cleanup()
            _global_loop = None

    @classmethod
    def create_timer(cls, timeout, callback):
        timer = Timer(timeout, callback)
        _global_loop.add_timer(timer)
        return timer

    def __init__(self, *args, **kwargs):
        Connection.__init__(self, *args, **kwargs)

        self.deque = deque()
        self._deque_lock = Lock()
        self._connect_socket()
        self._socket.setblocking(0)

        with _global_loop._lock:
            self._read_watcher = libev.IO(self._socket.fileno(), libev.EV_READ, _global_loop._loop, self.handle_read)
            self._write_watcher = libev.IO(self._socket.fileno(), libev.EV_WRITE, _global_loop._loop, self.handle_write)

        self._send_options_message()

        _global_loop.connection_created(self)

        # start the global event loop if needed
        _global_loop.maybe_start()

    def close(self):
        with self.lock:
            if self.is_closed:
                return
            self.is_closed = True

        log.debug("Closing connection (%s) to %s", id(self), self.endpoint)

        _global_loop.connection_destroyed(self)
        self._socket.close()
        log.debug("Closed socket to %s", self.endpoint)

        # don't leave in-progress operations hanging
        if not self.is_defunct:
            self.error_all_requests(
                ConnectionShutdown("Connection to %s was closed" % self.endpoint))

    def handle_write(self, watcher, revents, errno=None):
        if revents & libev.EV_ERROR:
            if errno:
                exc = IOError(errno, os.strerror(errno))
            else:
                exc = Exception("libev reported an error")

            self.defunct(exc)
            return

        while True:
            try:
                with self._deque_lock:
                    next_msg = self.deque.popleft()
            except IndexError:
                if not self._socket_writable:
                    self._socket_writable = True
                return

            try:
                sent = self._socket.send(next_msg)
            except socket.error as err:
                if (err.args[0] in NONBLOCKING or
                        err.args[0] in (ssl.SSL_ERROR_WANT_READ, ssl.SSL_ERROR_WANT_WRITE)):
                    if err.args[0] in NONBLOCKING:
                        self._socket_writable = False
                    with self._deque_lock:
                        self.deque.appendleft(next_msg)
                else:
                    self.defunct(err)
                return
            else:
                if sent < len(next_msg):
                    with self._deque_lock:
                        self.deque.appendleft(next_msg[sent:])
                    # we've seen some cases that 0 is returned instead of NONBLOCKING. But usually,
                    # we don't expect this to happen. https://bugs.python.org/issue20951
                    if sent == 0:
                        self._socket_writable = False
                        return

    def handle_read(self, watcher, revents, errno=None):
        if revents & libev.EV_ERROR:
            if errno:
                exc = IOError(errno, os.strerror(errno))
            else:
                exc = Exception("libev reported an error")

            self.defunct(exc)
            return
        try:
            while True:
                buf = self._socket.recv(self.in_buffer_size)
                self._iobuf.write(buf)
                if len(buf) < self.in_buffer_size:
                    break
        except socket.error as err:
            if isinstance(err, ssl.SSLError):
                if err.args[0] in (ssl.SSL_ERROR_WANT_READ, ssl.SSL_ERROR_WANT_WRITE):
                    if not self._iobuf.tell():
                        return
                else:
                    self.defunct(err)
                    return
            elif err.args[0] in NONBLOCKING:
                if not self._iobuf.tell():
                    return
            else:
                self.defunct(err)
                return

        if self._iobuf.tell():
            self.process_io_buffer()
        else:
            log.debug("Connection %s closed by server", self)
            self.close()

    def push(self, data):
        sabs = self.out_buffer_size
        if len(data) > sabs:
            chunks = []
            for i in range(0, len(data), sabs):
                chunks.append(data[i:i + sabs])
        else:
            chunks = [data]

        with self._deque_lock:
            self.deque.extend(chunks)
            _global_loop.notify()