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A Distributed Worker Launcher Framework

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crew_class_controller_group: Controller group class

crew_class_controller_group: Controller group class
In crew: A Distributed Worker Launcher Framework

crew_class_controller_groupR Documentation

Controller group class

Description

R6 class for controller groups.

Details

See crew_controller_group().

Active bindings

controllers

List of R6 controller objects.

relay

Relay object for event-driven programming on a downstream condition variable.

Methods

Public methods

Method new()

Multi-controller constructor.

Usage
crew_class_controller_group$new(controllers = NULL, relay = NULL)
Arguments
controllers

List of R6 controller objects.

relay

Relay object for event-driven programming on a downstream condition variable.

Returns

An R6 object with the controller group object.

Examples
if (identical(Sys.getenv("CREW_EXAMPLES"), "true")) {
persistent <- crew_controller_local(name = "persistent")
transient <- crew_controller_local(
  name = "transient",
  tasks_max = 1L
)
group <- crew_controller_group(persistent, transient)
group$start()
group$push(name = "task", command = sqrt(4), controller = "transient")
group$wait()
group$pop()
group$terminate()
}

Method validate()

Validate the client.

Usage
crew_class_controller_group$validate()
Returns

NULL (invisibly).

Method size()

Number of tasks in the selected controllers.

Usage
crew_class_controller_group$size(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

Non-negative integer, number of tasks in the controller.

Method empty()

See if the controllers are empty.

Usage
crew_class_controller_group$empty(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

A controller is empty if it has no running tasks or completed tasks waiting to be retrieved with push().

Returns

TRUE if all the selected controllers are empty, FALSE otherwise.

Method nonempty()

Check if the controller group is nonempty.

Usage
crew_class_controller_group$nonempty(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

A controller is empty if it has no running tasks or completed tasks waiting to be retrieved with push().

Returns

TRUE if the controller is empty, FALSE otherwise.

Method resolved()

Number of resolved mirai() tasks.

Usage
crew_class_controller_group$resolved(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

resolved() is cumulative: it counts all the resolved tasks over the entire lifetime of the controller session.

Returns

Non-negative integer of length 1, number of resolved mirai() tasks. The return value is 0 if the condition variable does not exist (i.e. if the client is not running).

Method unresolved()

Number of unresolved mirai() tasks.

Usage
crew_class_controller_group$unresolved(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

Non-negative integer of length 1, number of unresolved mirai() tasks.

Method saturated()

Check if a controller is saturated.

Usage
crew_class_controller_group$saturated(
  collect = NULL,
  throttle = NULL,
  controller = NULL
)
Arguments
collect

Deprecated in version 0.5.0.9003 (2023-10-02). Not used.

throttle

Deprecated in version 0.5.0.9003 (2023-10-02). Not used.

controller

Character vector of length 1 with the controller name. Set to NULL to select the default controller that push() would choose.

Details

A controller is saturated if the number of uncollected tasks is greater than or equal to the maximum number of workers. You can still push tasks to a saturated controller, but tools that use crew such as targets may choose not to (for performance and user-friendliness).

Returns

TRUE if all the selected controllers are saturated, FALSE otherwise.

Method start()

Start one or more controllers.

Usage
crew_class_controller_group$start(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

NULL (invisibly).

Method started()

Check whether all the given controllers are started.

Usage
crew_class_controller_group$started(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

Actually checks whether all the given clients are started.

Returns

TRUE if the controllers are started, FALSE if any are not.

Method launch()

Launch one or more workers on one or more controllers.

Usage
crew_class_controller_group$launch(n = 1L, controllers = NULL)
Arguments
n

Number of workers to launch in each controller selected.

controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

NULL (invisibly).

Method scale()

Automatically scale up the number of workers if needed in one or more controller objects.

Usage
crew_class_controller_group$scale(throttle = TRUE, controllers = NULL)
Arguments
throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

See the scale() method in individual controller classes.

Returns

Invisibly returns TRUE if there was any relevant auto-scaling activity (new worker launches or worker connection/disconnection events) (FALSE otherwise).

Method autoscale()

Run worker auto-scaling in a later loop.

Usage
crew_class_controller_group$autoscale(
  loop = later::current_loop(),
  controllers = NULL
)
Arguments
loop

A later loop to run auto-scaling.

controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

NULL (invisibly).

Method descale()

Terminate the auto-scaling loop started by controller$autoscale().

Usage
crew_class_controller_group$descale(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

NULL (invisibly).

Method crashes()

Report the number of consecutive crashes of a task, summed over all selected controllers in the group.

Usage
crew_class_controller_group$crashes(name, controllers = NULL)
Arguments
name

Character string, name of the task to check.

controllers

Not used. Included to ensure the signature is compatible with the analogous method of controller groups.

Details

See the crashes_max argument of crew_controller().

Returns

Number of consecutive crashes of the named task, summed over all the controllers in the group.

Method push()

Push a task to the head of the task list.

Usage
crew_class_controller_group$push(
  command,
  data = list(),
  globals = list(),
  substitute = TRUE,
  seed = NULL,
  algorithm = NULL,
  packages = character(0),
  library = NULL,
  seconds_timeout = NULL,
  scale = TRUE,
  throttle = TRUE,
  name = NULL,
  save_command = NULL,
  controller = NULL
)
Arguments
command

Language object with R code to run.

data

Named list of local data objects in the evaluation environment.

globals

Named list of objects to temporarily assign to the global environment for the task. See the reset_globals argument of crew_controller_local().

substitute

Logical of length 1, whether to call base::substitute() on the supplied value of the command argument. If TRUE (default) then command is quoted literally as you write it, e.g. push(command = your_function_call()). If FALSE, then crew assumes command is a language object and you are passing its value, e.g. push(command = quote(your_function_call())). substitute = TRUE is appropriate for interactive use, whereas substitute = FALSE is meant for automated R programs that invoke crew controllers.

seed

Integer of length 1 with the pseudo-random number generator seed to set for the evaluation of the task. Passed to the seed argument of set.seed() if not NULL. If algorithm and seed are both NULL, then the random number generator defaults to the widely spaced worker-specific L'Ecuyer streams as supported by mirai::nextstream(). See vignette("parallel", package = "parallel") for details.

algorithm

Integer of length 1 with the pseudo-random number generator algorithm to set for the evaluation of the task. Passed to the kind argument of RNGkind() if not NULL. If algorithm and seed are both NULL, then the random number generator defaults to the recommended widely spaced worker-specific L'Ecuyer streams as supported by mirai::nextstream(). See vignette("parallel", package = "parallel") for details.

packages

Character vector of packages to load for the task.

library

Library path to load the packages. See the lib.loc argument of require().

seconds_timeout

Optional task timeout passed to the .timeout argument of mirai::mirai() (after converting to milliseconds).

scale

Logical, whether to automatically scale workers to meet demand. See the scale argument of the push() method of ordinary single controllers.

throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

name

Character string, name of the task. If NULL, a random name is automatically generated. The task name must not conflict with an existing task in the controller where it is submitted. To reuse the name, wait for the existing task to finish, then either pop() or collect() it to remove it from its controller.

save_command

Deprecated on 2025-01-22 (crew version 0.10.2.9004).

controller

Character of length 1, name of the controller to submit the task. If NULL, the controller defaults to the first controller in the list.

Returns

Invisibly return the mirai object of the pushed task. This allows you to interact with the task directly, e.g. to create a promise object with promises::as.promise().

Method synced()

Check if all controllers are synced.

Usage
crew_class_controller_group$synced(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

A controller is synced if all pushed tasks in the controller show up in the task counts in mirai::info().

Method walk()

Apply a single command to multiple inputs, and return control to the user without waiting for any task to complete.

Usage
crew_class_controller_group$walk(
  command,
  iterate,
  data = list(),
  globals = list(),
  substitute = TRUE,
  seed = NULL,
  algorithm = NULL,
  packages = character(0),
  library = NULL,
  seconds_timeout = NULL,
  names = NULL,
  save_command = NULL,
  verbose = interactive(),
  scale = TRUE,
  throttle = TRUE,
  controller = NULL
)
Arguments
command

Language object with R code to run.

iterate

Named list of vectors or lists to iterate over. For example, to run function calls f(x = 1, y = "a") and f(x = 2, y = "b"), set command to f(x, y), and set iterate to list(x = c(1, 2), y = c("a", "b")). The individual function calls are evaluated as f(x = iterate$x[[1]], y = iterate$y[[1]]) and f(x = iterate$x[[2]], y = iterate$y[[2]]). All the elements of iterate must have the same length. If there are any name conflicts between iterate and data, iterate takes precedence.

data

Named list of constant local data objects in the evaluation environment. Objects in this list are treated as single values and are held constant for each iteration of the map.

globals

Named list of constant objects to temporarily assign to the global environment for each task. This list should include any functions you previously defined in the global environment which are required to run tasks. See the reset_globals argument of crew_controller_local(). Objects in this list are treated as single values and are held constant for each iteration of the map.

substitute

Logical of length 1, whether to call base::substitute() on the supplied value of the command argument. If TRUE (default) then command is quoted literally as you write it, e.g. push(command = your_function_call()). If FALSE, then crew assumes command is a language object and you are passing its value, e.g. push(command = quote(your_function_call())). substitute = TRUE is appropriate for interactive use, whereas substitute = FALSE is meant for automated R programs that invoke crew controllers.

seed

Integer of length 1 with the pseudo-random number generator seed to set for the evaluation of the task. Passed to the seed argument of set.seed() if not NULL. If algorithm and seed are both NULL, then the random number generator defaults to the recommended widely spaced worker-specific L'Ecuyer streams as supported by mirai::nextstream(). See vignette("parallel", package = "parallel") for details.

algorithm

Integer of length 1 with the pseudo-random number generator algorithm to set for the evaluation of the task. Passed to the kind argument of RNGkind() if not NULL. If algorithm and seed are both NULL, then the random number generator defaults to the recommended widely spaced worker-specific L'Ecuyer streams as supported by mirai::nextstream(). See vignette("parallel", package = "parallel") for details.

packages

Character vector of packages to load for the task.

library

Library path to load the packages. See the lib.loc argument of require().

seconds_timeout

Optional task timeout passed to the .timeout argument of mirai::mirai() (after converting to milliseconds).

names

Optional character of length 1, name of the element of iterate with names for the tasks. If names is supplied, then iterate[[names]] must be a character vector.

save_command

Deprecated on 2025-01-22 (crew version 0.10.2.9004).

verbose

Logical of length 1, whether to print to a progress bar when pushing tasks.

scale

Logical, whether to automatically scale workers to meet demand. See also the throttle argument.

throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

controller

Character of length 1, name of the controller to submit the tasks. If NULL, the controller defaults to the first controller in the list.

Details

In contrast to walk(), map() blocks the local R session and waits for all tasks to complete.

Returns

Invisibly returns a list of mirai task objects for the newly created tasks. The order of tasks in the list matches the order of data in the iterate argument.

Method map()

Apply a single command to multiple inputs.

Usage
crew_class_controller_group$map(
  command,
  iterate,
  data = list(),
  globals = list(),
  substitute = TRUE,
  seed = NULL,
  algorithm = NULL,
  packages = character(0),
  library = NULL,
  seconds_interval = NULL,
  seconds_timeout = NULL,
  names = NULL,
  save_command = NULL,
  error = "stop",
  warnings = TRUE,
  verbose = interactive(),
  scale = TRUE,
  throttle = TRUE,
  controller = NULL
)
Arguments
command

Language object with R code to run.

iterate

Named list of vectors or lists to iterate over. For example, to run function calls f(x = 1, y = "a") and f(x = 2, y = "b"), set command to f(x, y), and set iterate to list(x = c(1, 2), y = c("a", "b")). The individual function calls are evaluated as f(x = iterate$x[[1]], y = iterate$y[[1]]) and f(x = iterate$x[[2]], y = iterate$y[[2]]). All the elements of iterate must have the same length. If there are any name conflicts between iterate and data, iterate takes precedence.

data

Named list of constant local data objects in the evaluation environment. Objects in this list are treated as single values and are held constant for each iteration of the map.

globals

Named list of constant objects to temporarily assign to the global environment for each task. This list should include any functions you previously defined in the global environment which are required to run tasks. See the reset_globals argument of crew_controller_local(). Objects in this list are treated as single values and are held constant for each iteration of the map.

substitute

Logical of length 1, whether to call base::substitute() on the supplied value of the command argument. If TRUE (default) then command is quoted literally as you write it, e.g. push(command = your_function_call()). If FALSE, then crew assumes command is a language object and you are passing its value, e.g. push(command = quote(your_function_call())). substitute = TRUE is appropriate for interactive use, whereas substitute = FALSE is meant for automated R programs that invoke crew controllers.

seed

Integer of length 1 with the pseudo-random number generator seed to set for the evaluation of the task. Passed to the seed argument of set.seed() if not NULL. If algorithm and seed are both NULL, then the random number generator defaults to the recommended widely spaced worker-specific L'Ecuyer streams as supported by mirai::nextstream(). See vignette("parallel", package = "parallel") for details.

algorithm

Integer of length 1 with the pseudo-random number generator algorithm to set for the evaluation of the task. Passed to the kind argument of RNGkind() if not NULL. If algorithm and seed are both NULL, then the random number generator defaults to the recommended widely spaced worker-specific L'Ecuyer streams as supported by mirai::nextstream(). See vignette("parallel", package = "parallel") for details.

packages

Character vector of packages to load for the task.

library

Library path to load the packages. See the lib.loc argument of require().

seconds_interval

Deprecated on 2025-01-17 (crew version 0.10.2.9003). Instead, the seconds_interval argument passed to crew_controller_group() is used as seconds_max in a crew_throttle() object which orchestrates exponential backoff.

seconds_timeout

Optional task timeout passed to the .timeout argument of mirai::mirai() (after converting to milliseconds).

names

Optional character of length 1, name of the element of iterate with names for the tasks. If names is supplied, then iterate[[names]] must be a character vector.

save_command

Deprecated on 2025-01-22 (crew version 0.10.2.9004).

error

Character vector of length 1, choice of action if a task has an error. Possible values:

  • "stop": throw an error in the main R session instead of returning a value. In case of an error, the results from the last errored map() are in the error field of the controller, e.g. controller_object$error. To reduce memory consumption, set controller_object$error <- NULL after you are finished troubleshooting.

  • "warn": throw a warning. This allows the return value with all the error messages and tracebacks to be generated.

  • "silent": do nothing special.

warnings

Logical of length 1, whether to throw a warning in the interactive session if at least one task encounters an error.

verbose

Logical of length 1, whether to print progress messages.

scale

Logical, whether to automatically scale workers to meet demand. See also the throttle argument.

throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

controller

Character of length 1, name of the controller to submit the tasks. If NULL, the controller defaults to the first controller in the list.

Details

The idea comes from functional programming: for example, the map() function from the purrr package.

Returns

A tibble of results and metadata: one row per task and columns corresponding to the output of pop().

Method pop()

Pop a completed task from the results data frame.

Usage
crew_class_controller_group$pop(
  scale = TRUE,
  collect = NULL,
  throttle = TRUE,
  error = NULL,
  controllers = NULL
)
Arguments
scale

Logical, whether to automatically scale workers to meet demand. See the scale argument of the pop() method of ordinary single controllers.

collect

Deprecated in version 0.5.0.9003 (2023-10-02). Not used.

throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

error

NULL or character of length 1, choice of action if the popped task threw an error. Possible values:

  • "stop": throw an error in the main R session instead of returning a value.

  • "warn": throw a warning.

  • NULL or "silent": do not react to errors.

controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

If there is no task to collect, return NULL. Otherwise, return a one-row tibble with the same columns as pop() for ordinary controllers.

Method collect()

Pop all available task results and return them in a tidy tibble.

Usage
crew_class_controller_group$collect(
  scale = TRUE,
  throttle = TRUE,
  error = NULL,
  controllers = NULL
)
Arguments
scale

Logical of length 1, whether to automatically call scale() to auto-scale workers to meet the demand of the task load.

throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

error

NULL or character of length 1, choice of action if the popped task threw an error. Possible values:

  • "stop": throw an error in the main R session instead of returning a value.

  • "warn": throw a warning.

  • NULL or "silent": do not react to errors.

controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

A tibble of results and metadata of all resolved tasks, with one row per task. Returns NULL if there are no available results.

Method wait()

Wait for tasks.

Usage
crew_class_controller_group$wait(
  mode = "all",
  seconds_interval = NULL,
  seconds_timeout = Inf,
  scale = TRUE,
  throttle = TRUE,
  controllers = NULL
)
Arguments
mode

Character string, name of the waiting condition. wait(mode = "all") waits until all tasks in the mirai compute profile resolve, and wait(mode = "one") waits until at least one task is available to push() or collect() from the controller. The former still works if the controller is not the only means of submitting tasks to the compute profile, whereas the latter assumes only the controller submits tasks.

seconds_interval

Deprecated on 2025-01-17 (crew version 0.10.2.9003). Instead, the seconds_interval argument passed to crew_controller_group() is used as seconds_max in a crew_throttle() object which orchestrates exponential backoff.

seconds_timeout

Timeout length in seconds waiting for results to become available.

scale

Logical of length 1, whether to call scale_later() on each selected controller to schedule auto-scaling. See the scale argument of the wait() method of ordinary single controllers.

throttle

TRUE to skip auto-scaling if it already happened within the last polling interval. FALSE to auto-scale every time scale() is called. Throttling avoids overburdening the local R process.

controllers

Character vector of controller names. Set to NULL to select all controllers.

Details

The wait() method blocks the calling R session until the condition in the mode argument is met. During the wait, wait() iteratively auto-scales the workers.

Returns

A logical of length 1, invisibly. wait(mode = "all") returns TRUE if all tasks in the mirai compute profile have resolved (FALSE otherwise). wait(mode = "one") returns TRUE if the controller is ready to pop or collect at least one resolved task (FALSE otherwise). wait(mode = "one") assumes all tasks were submitted through the controller and not by other means.

Method push_backlog()

Push the name of a task to the backlog.

Usage
crew_class_controller_group$push_backlog(name, controller = NULL)
Arguments
name

Character of length 1 with the task name to push to the backlog.

controller

Character vector of length 1 with the controller name. Set to NULL to select the default controller that push_backlog() would choose.

Details

pop_backlog() pops the tasks that can be pushed without saturating the controller.

Returns

NULL (invisibly).

Method pop_backlog()

Pop the task names from the head of the backlog which can be pushed without saturating the controller.

Usage
crew_class_controller_group$pop_backlog(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

Character vector of task names which can be pushed to the controller without saturating it. If the controller is saturated, character(0L) is returned.

Method summary()

Summarize the workers of one or more controllers.

Usage
crew_class_controller_group$summary(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

A data frame of aggregated worker summary statistics of all the selected controllers. It has one row per worker, and the rows are grouped by controller. See the documentation of the summary() method of the controller class for specific information about the columns in the output.

Method pids()

Deprecated on 2025-08-26 in crew version 1.2.1.9005.

Usage
crew_class_controller_group$pids(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

The integer process ID of the current process.

Method terminate()

Terminate the workers and disconnect the client for one or more controllers.

Usage
crew_class_controller_group$terminate(controllers = NULL)
Arguments
controllers

Character vector of controller names. Set to NULL to select all controllers.

Returns

NULL (invisibly).

See Also

Other controller_group: crew_controller_group()

Examples

if (identical(Sys.getenv("CREW_EXAMPLES"), "true")) {
persistent <- crew_controller_local(name = "persistent")
transient <- crew_controller_local(
  name = "transient",
  tasks_max = 1L
)
group <- crew_controller_group(persistent, transient)
group$start()
group$push(name = "task", command = sqrt(4), controller = "transient")
group$wait()
group$pop()
group$terminate()
}

## ------------------------------------------------
## Method `crew_class_controller_group$new`
## ------------------------------------------------

if (identical(Sys.getenv("CREW_EXAMPLES"), "true")) {
persistent <- crew_controller_local(name = "persistent")
transient <- crew_controller_local(
  name = "transient",
  tasks_max = 1L
)
group <- crew_controller_group(persistent, transient)
group$start()
group$push(name = "task", command = sqrt(4), controller = "transient")
group$wait()
group$pop()
group$terminate()
}

crew documentation built on Sept. 4, 2026, 9:07 a.m.

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