AWS Code Sample
Catalog demonstrates how to create a separate process to handle notification messages for an Elastic Transcoder job.

# Copyright 2010-2019, Inc. or its affiliates. All Rights Reserved. # # This file is licensed under the Apache License, Version 2.0 (the "License"). # You may not use this file except in compliance with the License. A copy of the # License is located at # # # # This file 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. from ctypes import c_bool from enum import Enum, auto import json import multiprocessing import pprint import boto3 class JobStatus(Enum): """Status of an Elastic Transcoder job""" SUCCESS = auto() # Elastic Transcoder job finished successfully ERROR = auto() # Elastic Transcoder job failed RUNNING = auto() # Job is running UNKNOWN = auto() # SqsWorker process was aborted class ProcessStatus(Enum): """Status of an SqsWorker process""" READY = auto() # Initialized, but not yet started IN_PROGRESS = auto() # Started and monitoring notifications ABORTED = auto() # Aborted before Elastic Transcoder job finished FINISHED = auto() # Finished after handling all job notifications class SqsWorker: """Monitors SQS notifications for an Elastic Transcoder job Each Elastic Transcoder job/JobMonitor must have its own SqsWorker object. The SqsWorker handles messages for the job. Messages for other jobs are ignored. The SysWorker performs its task in a separate process. The JobMonitor starts the process by calling SysWorker.start(). While the SysWorker process is handling job notifications, the JobMonitor parent process can perform other tasks, including starting new jobs with new JobMonitor and SqsWorker objects. When the Transcoder job is finished, a SysWorker flag is set. The JobMonitor parent process must periodically retrieve the current setting of the flag by calling SysWorker.finished(). When the Trancoder job has finished, the JobMonitor parent process must terminate the SysWorker process by calling SysWorker.stop(). The final result of the completed job can be retrieved by calling SysWorker.job_status(). """ def __init__(self, job_id, sqs_queue_name): """Initialize an SqsWorker object to process SQS notification messages for a particular Elastic Transcoder job. :param job_id: string; Elastic Transcoder job ID to monitor :param sqs_queue_name: string; Name of SQS queue subscribed to receive notifications for job_id """ self._job_id = job_id self._finished = multiprocessing.Value(c_bool, False) self._job_status = multiprocessing.Value('i', JobStatus.RUNNING.value) self._process_status = multiprocessing.Value('i', ProcessStatus.READY.value) self._args = (job_id, sqs_queue_name, self._finished, self._job_status, self._process_status) self._process = None def start(self): """Start a new SqsWorker process to handle the job's notifications""" if self._process is not None: raise RuntimeError('SqsQueueNotificationWorker already running.') self._process = multiprocessing.Process(target=poll_and_handle_messages, args=self._args) self._process.start() self._process_status.value = ProcessStatus.IN_PROGRESS.value def stop(self): """Stop the SqsWorker process""" if self._process is None: raise RuntimeError('SqsQueueNotificationWorker already stopped.') if self._process.is_alive(): # Aborting the process before the job is finished self._process_status.value = ProcessStatus.ABORTED.value self._job_status.value = JobStatus.UNKNOWN.value self._finished.value = True self._process.join() def finished(self): """Finished = Job completed successfully or job terminated with error or monitoring of notifications was aborted before receiving a job-completed notification """ return self._finished.value def job_status(self): return JobStatus(self._job_status.value) def process_status(self): return ProcessStatus(self._process_status.value) def __repr__(self): return f'SqsWorker(Job ID: {self._job_id}, Status: {ProcessStatus(self._process_status.value).name})' def poll_and_handle_messages(job_id, sqs_queue_name, finished, job_status, process_status): """Process SQS notifications for a particular Elastic Transcoder job This method runs as a separate process. :param job_id: string; Elastic Transcoder job ID to monitor :param sqs_queue_name: string; Name of SQS queue :param finished: boolean; Shared memory flag. While this method is running, the flag might be set externally if the JobMonitor parent process instructs us to stop before we receive notification that the job has finished. Otherwise, this method sets the finished flag when the Transcoder job finishes. :param job_status: int/JobStatus enum; Shared memory variable containing the Transcoder job status :param process_status: int/ProcessStatus enum; Shared memory variable containing the SysWorker process status """ sqs_client = boto3.client('sqs') response = sqs_client.get_queue_url(QueueName=sqs_queue_name) sqs_queue_url = response['QueueUrl'] # Loop until the job is finished or the JobMonitor parent process instructs # us to stop while not finished.value: response = sqs_client.receive_message(QueueUrl=sqs_queue_url, MaxNumberOfMessages=5, WaitTimeSeconds=5,) # Any messages received? if 'Messages' not in response: continue # Process each message for message in response['Messages']: # Extract the message part of the body notification = json.loads(json.loads(message['Body'])['Message']) # Show the notification information print('Notification:') pprint.pprint(notification) # Is the message for this job? if notification['jobId'] == job_id: # Delete the message from the queue sqs_client.delete_message(QueueUrl=sqs_queue_url, ReceiptHandle=message['ReceiptHandle']) # Did the job finish, either successfully or with error? if notification['state'] == 'COMPLETED': # Set shared memory flags job_status.value = JobStatus.SUCCESS.value process_status.value = ProcessStatus.FINISHED.value finished.value = True elif notification['state'] == 'ERROR': job_status.value = JobStatus.ERROR.value process_status.value = ProcessStatus.FINISHED.value finished.value = True

Sample Details

Service: elastictranscoder

Last tested: 2019-02-04

Author: AWS

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