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92 lines
3.2 KiB
Python
92 lines
3.2 KiB
Python
# dispatcharr/persistent_lock.py
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import uuid
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import redis
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class PersistentLock:
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"""
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A persistent, auto-expiring lock that uses Redis.
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Usage:
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1. Instantiate with a Redis client, a unique lock key (e.g. "lock:account:123"),
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and an optional timeout (in seconds).
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2. Call acquire() to try to obtain the lock.
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3. Optionally, periodically call refresh() to extend the lock's lifetime.
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4. When finished, call release() to free the lock.
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"""
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def __init__(self, redis_client: redis.Redis, lock_key: str, lock_timeout: int = 120):
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"""
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Initialize the lock.
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:param redis_client: An instance of redis.Redis.
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:param lock_key: The unique key for the lock.
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:param lock_timeout: Time-to-live for the lock in seconds.
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"""
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self.redis_client = redis_client
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self.lock_key = lock_key
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self.lock_timeout = lock_timeout
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self.lock_token = None
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self.has_lock = False
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def has_lock(self) -> bool:
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return self.has_lock
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def acquire(self) -> bool:
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"""
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Attempt to acquire the lock. Returns True if successful.
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"""
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self.lock_token = str(uuid.uuid4())
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# Set the lock with NX (only if not exists) and EX (expire time)
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result = self.redis_client.set(self.lock_key, self.lock_token, nx=True, ex=self.lock_timeout)
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if result is not None:
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self.has_lock = True
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return result is not None
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def refresh(self) -> bool:
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"""
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Refresh the lock's expiration time if this instance owns the lock.
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Returns True if the expiration was successfully extended.
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"""
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current_value = self.redis_client.get(self.lock_key)
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if current_value and current_value.decode("utf-8") == self.lock_token:
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self.redis_client.expire(self.lock_key, self.lock_timeout)
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self.has_lock = False
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return True
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return False
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def release(self) -> bool:
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"""
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Release the lock only if owned by this instance.
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Returns True if the lock was successfully released.
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"""
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# Use a Lua script for atomicity: only delete if the token matches.
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lua_script = """
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if redis.call("get", KEYS[1]) == ARGV[1] then
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return redis.call("del", KEYS[1])
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else
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return 0
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end
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"""
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release_lock = self.redis_client.register_script(lua_script)
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result = release_lock(keys=[self.lock_key], args=[self.lock_token])
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return result == 1
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# Example usage (for testing purposes only):
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if __name__ == "__main__":
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# Connect to Redis on localhost; adjust connection parameters as needed.
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client = redis.Redis(host="localhost", port=6379, db=0)
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lock = PersistentLock(client, "lock:example_account", lock_timeout=120)
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if lock.acquire():
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print("Lock acquired successfully!")
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# Do work here...
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# Optionally refresh the lock periodically:
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if lock.refresh():
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print("Lock refreshed.")
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# Finally, release the lock:
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if lock.release():
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print("Lock released.")
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else:
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print("Failed to release lock.")
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else:
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print("Failed to acquire lock.")
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