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#!/usr/bin/python3
import asyncio
import asyncpg
import json
class JobQueue(object):
def __init__(self):
self._pool = None
async def connect(self, **args):
"""Connect the database."""
self._pool = await asyncpg.create_pool(**args)
async def setup(self):
"""Initialize the database."""
async with self._pool.acquire() as con:
await con.execute("""
CREATE TABLE IF NOT EXISTS
jobs (
id SERIAL,
priority INT DEFAULT 0,
status TEXT DEFAULT 'open',
type TEXT,
payload JSONB
)
""")
async def request(self, jobtype, payload, priority=0):
"""Create a new job."""
async with self._pool.acquire() as con:
await con.execute("""
INSERT INTO jobs(type, payload, priority)
VALUES($1, $2, $3)
""", jobtype, json.dumps(payload), priority)
async def acquire(self, jobtype):
"""Mark a job as running, return id, payload and priority.
Return (None, None, None) if no job is available."""
async with self._pool.acquire() as con:
while True:
try:
# do not allow async access
async with con.transaction(isolation="serializable"):
result = await con.fetchrow("""
SELECT id, payload, priority
FROM jobs WHERE
type=$1 AND status='open'
ORDER BY priority DESC
""", jobtype)
if result is None:
# no jobs available
return None, None, None
jobid, payload, priority = result
await con.execute("""
UPDATE jobs
SET status='running'
WHERE id=$1
""", jobid)
return jobid, json.loads(payload), priority
except asyncpg.exceptions.SerializationError:
# job is being picked up by another worker, try again
pass
async def finish(self, jobid):
"""Mark a job as completed."""
async with self._pool.acquire() as con:
while True:
try:
async with con.transaction(isolation="serializable"):
await con.execute("""
UPDATE jobs
SET status='finished'
WHERE id=$1
""", jobid)
return
except asyncpg.exceptions.SerializationError:
pass
async def cleanup(self):
"""Reopen all unfinished jobs."""
async with self._pool.acquire() as con:
while True:
try:
async with con.transaction(isolation="serializable"):
await con.execute("""
UPDATE jobs
SET status='open'
WHERE status='running'
""")
return
except asyncpg.exceptions.SerializationError:
pass
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