Queue

The Queue block will gather incoming signals and emit a configurable 'chunk size' of signals at a configurable 'interval'. If incoming signals would overflow the queue 'capacity', the oldest signals are dropped from the queue and not emitted to the next block.

Properties

• backup_interval: Period at which queues are backed up to disk using persistance. Queues are also backed up on stop.
• capacity: Size of each queue. When the queue exceeds capacity, the oldest signals are dropped from the queue and not notified.
• chunk_size: Number of signals to emit at each interval or emit command.
• group_by: Signal attribute that determines what queue to put the signal in. Defaults to group null if attribute does not exist or group_by is unspecified.
• interval: Period at which signals are emitted from queues. If 0, signals will not be emitted only after processing imcoming signals, rather than at an interval. Note: It may be necessary to enable Auto Reload for this to work as intended.
• load_from_persistence: If True, after stopping the block, the previous state of the block (queue time remaining) will be loaded upon restart.
• reload: If True, emitted signals immediately get reloaded back into the end of the queue.
• uniqueness: If specified, each queue (i.e. group_by) will not allow multiple signals that evaluate to the same uniqueness. If a signal comes in that matches group_by and uniqueness with a signal already in the queue, then the new signal is dropped from the queue.
• update: If True and a uniqueness expression is set, incoming signals that would have been rejected by the uniqueness expression instead replace the signal that was competing with the incoming signal for uniqueness.

Inputs

• default: Any list of signals.

Outputs

• default: List of signals emitted from queues each interval period and emit command.

Commands

• emit: Emit signals off the end of the queues.
• groups: Returns a list of the block’s current signal groupings.
• remove: Remove signals from the queue group where query evaluates to True. Query uses the Expression Property syntax for evaluatuation. For example, to remove all signals, use {{True}} or to remove signals with val equal to 1 use {{$val == 1}}. If no group is specified, then all groups are inspected. Signals are not notified.
• update_props: Modify the value of a property on a started block. Parameter props is a dictionary where the key is a block property and the value is the new value. interval is the only property currently supported. When interval is updated, the recurring emit job will be cancelled and restarted, even if the new value is equal to the previous one.
• view: View signals in the queue group. If group is not specified, all signals in all queues are returned. Signals are not notified.

Dependencies

None