3a23c54723
The beat schedule is set to once per minute for each of the three environment provisioning tasks. Adding a beat schedule surfaced two problems that are addressed here with the following changes: - Commit the SQLALchemy session in order to release the environment lock. Otherwise the change to the `claimed_until` field is not persisted. - Set `none_as_null` on the JSOB fields on the `Environment`. This avoids problems with querying on Postgres JSON fields that are empty. This also adds a small change to the development command for the Celery worker. Multiple child processes were executing the beat jobs, which lead to exceptions for environment locks and confusing log output. This contrains the dev command to a single Celery worker.
51 lines
1.6 KiB
Python
51 lines
1.6 KiB
Python
from sqlalchemy import func, sql, Interval, and_, or_
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from contextlib import contextmanager
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from atst.database import db
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from atst.domain.exceptions import ClaimFailedException
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@contextmanager
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def claim_for_update(resource, minutes=30):
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"""
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Claim a mutually exclusive expiring hold on a resource.
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Uses the database as a central source of time in case the server clocks have drifted.
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Args:
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resource: A SQLAlchemy model instance with a `claimed_until` attribute.
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minutes: The maximum amount of time, in minutes, to hold the claim.
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"""
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Model = resource.__class__
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claim_until = func.now() + func.cast(
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sql.functions.concat(minutes, " MINUTES"), Interval
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)
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# Optimistically query for and update the resource in question. If it's
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# already claimed, `rows_updated` will be 0 and we can give up.
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rows_updated = (
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db.session.query(Model)
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.filter(
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and_(
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Model.id == resource.id,
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or_(Model.claimed_until == None, Model.claimed_until <= func.now()),
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)
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)
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.update({"claimed_until": claim_until}, synchronize_session="fetch")
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)
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if rows_updated < 1:
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raise ClaimFailedException(resource)
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# Fetch the claimed resource
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claimed = db.session.query(Model).filter_by(id=resource.id).one()
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try:
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# Give the resource to the caller.
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yield claimed
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finally:
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# Release the claim.
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db.session.query(Model).filter(Model.id == resource.id).filter(
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Model.claimed_until != None
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).update({"claimed_until": None}, synchronize_session="fetch")
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db.session.commit()
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