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redis_connection = StrictRedis(host='redis')
# source: https://redis.io/topics/distlock
# This will be used to release lock IF AND ONLY IF we have acquired it
REMOVE_ONLY_IF_OWNER_SCRIPT = \
"""if redis.call("get",KEYS[1]) == ARGV[1] then
return redis.call("del",KEYS[1])
else
return 0
end
"""
@contextmanager
def redis_lock(lock_name, expires=60):
# first, get a random value (for ownership)
random_value = str(uuid.uuid4())
# execute SET {lock_name} {random_value} EX {expires} NX
lock_acquired = bool(
redis_connection.set(lock_name, random_value, ex=expires, nx=True)
)
logger.info(f'Lock acquired? {lock_name} for {expires} - {lock_acquired}')
yield lock_acquired
if lock_acquired:
# if lock was acquired, then try to release it BUT ONLY if we are the owner
# (i.e. value inside is identical to what we put there originally)
redis_connection.eval(REMOVE_ONLY_IF_OWNER_SCRIPT, 1, lock_name, random_value)
logger.info(f'Lock {lock_name} released!')
@app.task()
def periodic_task_with_lock():
"""
This task uses redis_lock context manager to ensure it is executed
only one at a time.
"""
with redis_lock('periodic_task_with_lock_lock', 10) as acquired:
if not acquired:
# abort if one failed to acquire the lock
logger.warning('Lock not acquired!')
return
# ok, lock acquired! Work as usual...
will_sleep_for = randint(5, 8)
logger.info(f'I will keep lock for {will_sleep_for}s')
sleep(will_sleep_for)
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