import logging import json import signal import sys from threading import Event, Lock from apscheduler.schedulers.background import BackgroundScheduler from datetime import datetime, timedelta from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler from threading import Thread from time import sleep from data.model import db logger = logging.getLogger(__name__) class JobException(Exception): """ A job exception is an exception that is caused by something being malformed in the job. When a worker raises this exception the job will be terminated and the retry will not be returned to the queue. """ pass class WorkerUnhealthyException(Exception): """ When this exception is raised, the worker is no longer healthy and will not accept any more work. When this is raised while processing a queue item, the item should be returned to the queue along with another retry. """ pass class WorkerStatusServer(HTTPServer): def __init__(self, worker, *args, **kwargs): HTTPServer.__init__(self, *args, **kwargs) self.worker = worker class WorkerStatusHandler(BaseHTTPRequestHandler): def do_GET(self): if self.path == '/status': # Return the worker status code = 200 if self.server.worker.is_healthy() else 503 self.send_response(code) self.send_header('Content-Type', 'text/plain') self.end_headers() self.wfile.write('OK') elif self.path == '/terminate': # Return whether it is safe to terminate the worker process code = 200 if self.server.worker.is_terminated() else 503 self.send_response(code) else: self.send_error(404) def do_POST(self): if self.path == '/terminate': try: self.server.worker.join() self.send_response(200) except: self.send_response(500) else: self.send_error(404) class Worker(object): def __init__(self, queue, poll_period_seconds=30, reservation_seconds=300, watchdog_period_seconds=60): self._sched = BackgroundScheduler() self._poll_period_seconds = poll_period_seconds self._reservation_seconds = reservation_seconds self._watchdog_period_seconds = watchdog_period_seconds self._stop = Event() self._terminated = Event() self._queue = queue self._current_item_lock = Lock() self.current_queue_item = None def process_queue_item(self, job_details): """ Return True if complete, False if it should be retried. """ raise NotImplementedError('Workers must implement run.') def watchdog(self): """ Function that gets run once every watchdog_period_seconds. """ pass def _close_db_handle(self): if not db.is_closed(): logger.debug('Disconnecting from database.') db.close() def is_healthy(self): return not self._stop.is_set() def is_terminated(self): return self._terminated.is_set() def extend_processing(self, seconds_from_now): with self._current_item_lock: if self.current_queue_item is not None: self._queue.extend_processing(self.current_queue_item, seconds_from_now) def run_watchdog(self): logger.debug('Running watchdog.') try: self.watchdog() except WorkerUnhealthyException: logger.error('The worker has encountered an error and will not take new jobs.') self.mark_current_incomplete(restore_retry=True) self._stop.set() def poll_queue(self): logger.debug('Getting work item from queue.') with self._current_item_lock: self.current_queue_item = self._queue.get() while True: # Retrieve the current item in the queue over which to operate. We do so under # a lock to make sure we are always retrieving an item when in a healthy state. current_queue_item = None with self._current_item_lock: current_queue_item = self.current_queue_item if current_queue_item is None: break logger.debug('Queue gave us some work: %s', current_queue_item.body) job_details = json.loads(current_queue_item.body) try: self.process_queue_item(job_details) self.mark_current_complete() except JobException: logger.warning('An error occurred processing request: %s', current_queue_item.body) self.mark_current_incomplete(restore_retry=False) except WorkerUnhealthyException: logger.error('The worker has encountered an error and will not take new jobs. Job is being requeued.') self._stop.set() self.mark_current_incomplete(restore_retry=True) finally: # Close the db handle periodically self._close_db_handle() if not self._stop.is_set(): with self._current_item_lock: self.current_queue_item = self._queue.get(processing_time=self._reservation_seconds) if not self._stop.is_set(): logger.debug('No more work.') def update_queue_metrics(self): self._queue.update_metrics() def start(self, start_status_server_port=None): if start_status_server_port is not None: # Start a status server on a thread server_address = ('', start_status_server_port) httpd = WorkerStatusServer(self, server_address, WorkerStatusHandler) server_thread = Thread(target=httpd.serve_forever) server_thread.daemon = True server_thread.start() logger.debug("Scheduling worker.") soon = datetime.now() + timedelta(seconds=.001) self._sched.start() self._sched.add_job(self.poll_queue, 'interval', seconds=self._poll_period_seconds, start_date=soon) self._sched.add_job(self.update_queue_metrics, 'interval', seconds=60, start_date=soon) self._sched.add_job(self.run_watchdog, 'interval', seconds=self._watchdog_period_seconds) signal.signal(signal.SIGTERM, self.terminate) signal.signal(signal.SIGINT, self.terminate) while not self._stop.wait(1): pass logger.debug('Waiting for running tasks to complete.') self._sched.shutdown() logger.debug('Finished.') self._terminated.set() # Wait forever if we're running a server while start_status_server_port is not None: sleep(60) def mark_current_incomplete(self, restore_retry=False): with self._current_item_lock: if self.current_queue_item is not None: self._queue.incomplete(self.current_queue_item, restore_retry=restore_retry) self.current_queue_item = None def mark_current_complete(self): with self._current_item_lock: if self.current_queue_item is not None: self._queue.complete(self.current_queue_item) self.current_queue_item = None def terminate(self, signal_num=None, stack_frame=None, graceful=False): if self._terminated.is_set(): sys.exit(1) else: logger.debug('Shutting down worker.') self._stop.set() if not graceful: # Give back the retry that we took for this queue item so that if it were down to zero # retries it will still be picked up by another worker self.mark_current_incomplete() def join(self): self.terminate(graceful=True)