photolib/photoapp/jobs.py

import queue
import logging
import cherrypy
from photoapp.dbutils import create_db_sessionmaker, cursorwrap
from photoapp.types import Job, JobTargetType, JobTarget, JobTargetStatus, Photo, PhotoSet, Tag, TagItem
from sqlalchemy import func


logger = logging.getLogger("jobs")


class JobSubscriber(object):
    """
    adapter between cherrypy bus and JobsClient
    """
    def __init__(self, client):
        self.client = client
        cherrypy.engine.subscribe("create-job", self.create_job)  # TODO make "create-job" a const somewhere?

    def create_job(self, name, targets):
        uuid = self.client.create_job(name, targets)
        self.client.notify_server(uuid)
        return uuid


class JobsClient(object):
    def __init__(self, dbengine, notifier):
        self.engine = dbengine
        self.session = create_db_sessionmaker(self.engine)
        self.notifier = notifier

    @cursorwrap
    def create_job(self, c, name, targets):
        """
        create a new job in the database

        targets: list of dict(
            type=JobTargetType.TYPE,
            targets=[1, 2, 3]
        )
        """
        job_targets = []

        for target in targets:
            for target_id in target["targets"]:
                job_targets.append(
                    JobTarget(target_type=target["type"],
                              target=target_id)
                )

        j = Job(
            job_name=name,
            targets=job_targets,
        )

        c.add(j)
        c.commit()

        return j.uuid

    def notify_server(self, uuid):
        """
        notify the job execution server of a job that needs processing because it had been added/updated
        """
        self.notifier(uuid)


class PhotoappTask(object):
    def run_targets(self):
        raise NotImplementedError()


class LolTask(PhotoappTask):
    pass


"""
this is the list of job actions the system supports. The dict's keys match with the database Job objs' `job_name` column
"""
task_definitions = {
    "loljob": LolTask
}


class BaseJobServer(object):
    #TODO subclass this out in way that supports sqlite - below implementation's logic relies on with_for_update()
    pass


class JobServer(BaseJobServer):
    """
    job executor service. This object orchestrates job running by doing:
        - in any case, locking the job rows via sql
        - listening to notifications about new jobs
            - populate JobTargetStatus
        - looking for JobTargetStatus that can be claimed and worked on
            - executing the work
    """
    def __init__(self, dbengine):
        self.engine = dbengine
        self.session = create_db_sessionmaker(self.engine)

    def handle_notify(self, c, job_uuid):
        """
        notify the jobserver that a job needs to be processed. The job may be in any state, including locked. The job
        should be processed as follows:
        JobStatus.paused: do nothing
        JobStatus.done: do nothing
        JobStatus.error: do nothing
        JobStatus.ready: change to running state and begin processing
        JobStatus.running: begin processing.

        processing:
        - the job is added to a list of "watched" jobs
        - we issue a query looking for work
            - if no work is found, the job status is changed to Done (or error if any done work has error status?)
        """
        raise NotImplementedError()


class ThreadedJobServer(JobServer):
    def __init__(self, dbengine):
        """
        a version of the jobserver that runs as a thread
        """
        super().__init__(dbengine)
        self.notifyq = queue.Queue()
        self.work_notifyq = queue.Queue()

    @cursorwrap
    def handle_notify(self, c, job_uuid):
        # query the db for the target job, and lock it
        job = c.query(Job).filter(Job.uuid == job_uuid).first()

        # get the task we're running
        # task = task_definitions[job.job_name]()
        # logging.info("task: %s", task)

        # check if JobTargetStatus has been populated for this job
        statuses = c.query(func.count(JobTargetStatus.id)).join(JobTarget).filter(JobTarget.job_id == job.id).first()[0]

        if statuses == 0:
            # populate statuses
            logging.info("preparing statuses for job %s/%s", job.id, job.uuid)
            photo_ids = set()

            for target in c.query(JobTarget).filter(JobTarget.job_id == job.id).all():
                if target.target_type == JobTargetType.photo:
                    photo_ids.update([target.target])
                elif target.target_type == JobTargetType.photoset:
                    for photo in c.query(Photo.id).filter(Photo.set_id == target.target).all():
                        photo_ids.update([photo[0]])
                elif target.target_type == JobTargetType.tag:
                    for photo in c.query(Photo.id). \
                            join(PhotoSet).join(TagItem).join(Tag). \
                            filter(Tag.id == target.target). \
                            all():
                        photo_ids.update([photo[0]])

            for photo_id in photo_ids:
                c.add(JobTargetStatus(target_id=target.id, job_id=job.id, photo_id=photo_id))

            c.commit()  # if this fails, somebody else is handling job

    def queue_notify(self, job_uuid):
        self.notifyq.put(job_uuid)

    def run_background(self):
        from threading import Thread
        Thread(target=self.run_notifier, daemon=True).start()
        Thread(target=self.run_work, daemon=True).start()

    def run_notifier(self):
        while True:
            try:
                job_uuid = self.notifyq.get(timeout=5.0)
                self.handle_notify(job_uuid)
                self.work_notifyq.put(job_uuid)
            except queue.Empty:
                pass

    def run_work(self):
        # start a ThreadPoolExecutor
        # in a loop:
        # - poll the database for work, locking and then marking rows we claim
        # - poll self.work_notifyq
        # - submit it to the pool
        # - wait for pool results
        # - update the db with job results
        pass