Class LastValue<Value>Internal

Stores the last value received, can receive at most one value per step.

Since update is only called once per step and value can only be of length 1, LastValue always stores the last value of a single node. If multiple nodes attempt to write to this channel in a single step, an error will be thrown.

Type Parameters

  • Value

Hierarchy (view full)

Constructors

constructor

Properties

UpdateType ValueType lc_graph_name value?

Methods

checkpoint consume fromCheckpoint get update

Constructors

constructor

Properties

UpdateType

UpdateType: Value

ValueType

ValueType: Value

lc_graph_name

lc_graph_name: string

The name of the channel.

Optional value

value?: Value

Methods

checkpoint

  • checkpoint(): Value

  • Return a string representation of the channel's current state.

    Returns Value

    Throws

    if the channel is empty (never updated yet), or doesn't support checkpoints.

consume

  • consume(): boolean

  • Mark the current value of the channel as consumed. By default, no-op. This is called by Pregel before the start of the next step, for all channels that triggered a node. If the channel was updated, return true.

    Returns boolean

fromCheckpoint

  • fromCheckpoint(checkpoint?): this

  • Return a new identical channel, optionally initialized from a checkpoint. Can be thought of as a "restoration" from a checkpoint which is a "snapshot" of the channel's state.

    Parameters

    • Optional checkpoint: Value

    Returns this

get

  • get(): Value

  • Return the current value of the channel.

    Returns Value

    Throws

    if the channel is empty (never updated yet).

update

  • update(values): boolean

  • Update the channel's value with the given sequence of updates. The order of the updates in the sequence is arbitrary. This method is called by Pregel for all channels at the end of each step. If there are no updates, it is called with an empty sequence.

    Raises InvalidUpdateError if the sequence of updates is invalid. Returns True if the channel was updated, False otherwise.

    Parameters

    Returns boolean

    Throws

    if the sequence of updates is invalid.

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