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R6 Class Representing a Task List

Source: R/task_list.R
TaskList.Rd

A TaskList stores and retrieves one or more tasks.

Details

The TaskList class is used as a storage class. It provides a container that holds a collection of Task objects, along with a collection of methods for adding, removing, and getting Tasks. It can also report on the status of the Tasks contained within the list and retrieve results from those Tasks. What it cannot do is manage interactions with Workers or arrange for the Tasks to be executed. That's the job of the Queue.

Methods

Public methods

Method new()

Create a new task list

Usage

TaskList$new()

Method length()

Return the number of tasks in the list

Usage

TaskList$length()

Returns

Integer

Method add_task()

Add a task to the TaskList

Usage

TaskList$add_task(task)

Arguments

task

The Task object to be added

Method remove_task()

This method removes one or more tasks from the TaskList.

Usage

TaskList$remove_task(x)

Arguments

x

Indices of the tasks to be removed

Method get_task()

Return a single Task contained in the TaskList. The Task is not removed from the TaskList, and has reference semantics: if the listed task is completed by a Worker, then the status of any Task returned by this method will update automatically

Usage

TaskList$get_task(x)

Arguments

x

The index the task to return

Returns

A Task object

Method get_state()

Return the status of all tasks in the TaskList.

Usage

TaskList$get_state()

Returns

A character vector specifying the completion status for all listed tasks

Method get_tasks_in_state()

Return a list of tasks in a given state

Usage

TaskList$get_tasks_in_state(x)

Arguments

x

The name of the state (e.g., "waiting")

Returns

A TaskList object

Method retrieve()

Retrieves the current state of all tasks.

Usage

TaskList$retrieve()

Returns

Returns a tibble containing the results of all tasks and various other useful metadata. Contains one row per task in the TaskList, and the following columns:

  • task_id A character string specifying the task identifiers

  • worker_id An integer specifying the worker process ids (pid)

  • state A character string indicating the status of each task ("created", "waiting", "assigned", "running", or "done")

  • result A list containing the function outputs, or NULL

  • runtime Completion time for the task (NA if the task is not done)

  • fun A list containing the functions

  • args A list containing the arguments passed to each function

  • created The time at which each task was created

  • queued The time at which each task was added to a Queue

  • assigned The time at which each task was assigned to a Worker

  • started The time at which a Worker called each function

  • finished The time at which a Worker output was returned for the task

  • code The status code returned by the callr R session (integer)

  • message The message returned by the callr R session (character)

  • stdout List column containing the contents of stdout during function execution

  • stderr List column containing the contents of stderr during function execution

  • error List column containing NULL values

If all tasks have completed this output is the same as the output as the run() method for a Queue object.

Note: at present there is one field from the callr rsession::read() method that isn't captured here, and that's the error field. I'll add that after I've finished wrapping my head around what that actually does. The error column, at present, is included only as a placeholder

Method clone()

The objects of this class are cloneable with this method.

Usage

TaskList$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.