def consume_use(self, trust_id):
with sql.transaction() as session:
ref = (session.query(TrustModel).with_lockmode('update').filter_by(
deleted_at=None).filter_by(id=trust_id).first())
if ref is None:
raise exception.TrustNotFound(trust_id=trust_id)
if ref.remaining_uses is None:
# unlimited uses, do nothing
pass
elif ref.remaining_uses > 0:
ref.remaining_uses -= 1
else:
raise exception.TrustUseLimitReached(trust_id=trust_id)
def consume_use(self, trust_id):
try:
orig_ref = self.db.get('trust-%s' % trust_id)
except exception.NotFound:
raise exception.TrustNotFound(trust_id=trust_id)
remaining_uses = orig_ref.get('remaining_uses')
if remaining_uses is None:
# unlimited uses, do nothing
return
elif remaining_uses > 0:
ref = copy.deepcopy(orig_ref)
ref['remaining_uses'] -= 1
self.db.set('trust-%s' % trust_id, ref)
else:
raise exception.TrustUseLimitReached(trust_id=trust_id)
def consume_use(self, trust_id):
for attempt in range(MAXIMUM_CONSUME_ATTEMPTS):
with sql.transaction() as session:
try:
query_result = (session.query(TrustModel.remaining_uses).
filter_by(id=trust_id).
filter_by(deleted_at=None).one())
except sql.NotFound:
raise exception.TrustNotFound(trust_id=trust_id)
remaining_uses = query_result.remaining_uses
if remaining_uses is None:
# unlimited uses, do nothing
break
elif remaining_uses > 0:
# NOTE(morganfainberg): use an optimistic locking method
# to ensure we only ever update a trust that has the
# expected number of remaining uses.
rows_affected = (
session.query(TrustModel).
filter_by(id=trust_id).
filter_by(deleted_at=None).
filter_by(remaining_uses=remaining_uses).
update({'remaining_uses': (remaining_uses - 1)},
synchronize_session=False))
if rows_affected == 1:
# Successfully consumed a single limited-use trust.
# Since trust_id is the PK on the Trust table, there is
# no case we should match more than 1 row in the
# update. We either update 1 row or 0 rows.
break
else:
raise exception.TrustUseLimitReached(trust_id=trust_id)
# NOTE(morganfainberg): Ensure we have a yield point for eventlet
# here. This should cost us nothing otherwise. This can be removed
# if/when oslo_db cleanly handles yields on db calls.
time.sleep(0)
else:
# NOTE(morganfainberg): In the case the for loop is not prematurely
# broken out of, this else block is executed. This means the trust
# was not unlimited nor was it consumed (we hit the maximum
# iteration limit). This is just an indicator that we were unable
# to get the optimistic lock rather than silently failing or
# incorrectly indicating a trust was consumed.
raise exception.TrustConsumeMaximumAttempt(trust_id=trust_id)