Autoscaler

Background thread to autoscale pool workers.

Attributes

Attribute	Type	Description
pool	ProcessPool	The process pool instance that this thread manages and scales based on workload.
mutex	threading.Lock = threading.Lock()	A threading lock used to ensure thread-safe operations when scaling or updating concurrency limits.
max_concurrency	int	The upper limit on the number of concurrent worker processes allowed in the pool.
min_concurrency	int = 0	The lower limit on the number of concurrent worker processes to maintain in the pool.
keepalive	float = AUTOSCALE_KEEPALIVE	The minimum time interval in seconds required between a scale-up event and a subsequent scale-down event.
_last_scale_up	float = null	A monotonic timestamp recording the last time the pool size was increased to prevent premature scaling down.
worker	[Worker](../../events/state/worker.md?sid=celery_events_state_worker) = null	The worker instance associated with this autoscaler, used to update consumer prefetch counts during scaling.

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Constructor

Signature

def Autoscaler(
    pool: object,
    max_concurrency: int,
    min_concurrency: int = 0,
    worker: object = None,
    keepalive: float = AUTOSCALE_KEEPALIVE,
    mutex: threading.Lock = None
)

Parameters

Name	Type	Description
pool	object	The process pool to be managed by the autoscaler.
max_concurrency	int	The maximum number of worker processes allowed in the pool.
min_concurrency	int = 0	The minimum number of worker processes to maintain.
worker	object = None	The worker instance associated with this autoscaler.
keepalive	float = AUTOSCALE_KEEPALIVE	The time interval to wait before scaling down processes.
mutex	threading.Lock = None	An optional mutex for thread-safe operations; defaults to a new threading.Lock.

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Methods

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body()

@classmethod
def body() - > null

Executes the main loop of the background thread to periodically evaluate and perform scaling operations.

Returns

Type	Description
null	Nothing is returned as this method runs in a continuous loop.

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maybe_scale()

@classmethod
def maybe_scale(
    req: object = null
) - > null

Triggers a scaling check and ensures the worker pool maintains its required state if scaling occurs.

Parameters

Name	Type	Description
req	object = null	The request object currently being processed, used to trigger scaling logic.

Returns

Type	Description
null	Nothing is returned.

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update()

@classmethod
def update(
    max: integer = null,
    min: integer = null
) - > tuple

Updates the concurrency boundaries and immediately adjusts the pool size if the current process count falls outside new limits.

Parameters

Name	Type	Description
max	integer = null	The new maximum number of concurrent worker processes allowed.
min	integer = null	The new minimum number of concurrent worker processes to maintain.

Returns

Type	Description
tuple	A tuple containing the updated (max_concurrency, min_concurrency) values.

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scale_up()

@classmethod
def scale_up(
    n: integer
) - > null

Increases the number of worker processes and updates the timestamp of the last scale-up event.

Parameters

Name	Type	Description
n	integer	The number of additional worker processes to spawn.

Returns

Type	Description
null	Nothing is returned.

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scale_down()

@classmethod
def scale_down(
    n: integer
) - > null

Decreases the number of worker processes, provided that the keepalive interval since the last scale-up has elapsed.

Parameters

Name	Type	Description
n	integer	The number of worker processes to terminate.

Returns

Type	Description
null	Nothing is returned.

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info()

@classmethod
def info() - > dict

Returns a dictionary containing the current configuration and operational status of the autoscaler.

Returns

Type	Description
dict	A dictionary with keys 'max', 'min', 'current', and 'qty' representing the autoscaler's state.

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qty()

@classmethod
def qty() - > integer

Calculates the number of reserved requests currently waiting to be processed.

Returns

Type	Description
integer	The count of requests currently in the reserved state.

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processes()

@classmethod
def processes() - > integer

Retrieves the current number of active worker processes in the pool.

Returns

Type	Description
integer	The total count of processes currently managed by the pool.

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