Skip to contents

Create a controller object from a client and launcher.

Source: R/crew_controller.R
crew_controller.Rd

This function is for developers of crew launcher plugins. Users should use a specific controller helper such as crew_controller_local().

Usage

crew_controller(
  client,
  launcher,
  crashes_max = 5L,
  backup = NULL,
  auto_scale = NULL
)

Arguments

client

An R6 client object created by crew_client().

launcher

An R6 launcher object created by one of the crew_launcher_*() functions such as crew_launcher_local().

crashes_max

In rare cases, a worker may exit unexpectedly before it completes its current task. If this happens, pop() returns a status of "crash" instead of "error" for the task. The controller does not automatically retry the task, but you can retry it manually by calling push() again and using the same task name as before. (However, targets pipelines running crew do automatically retry tasks whose workers crashed.)

crashes_max is a non-negative integer, and it sets the maximum number of allowable consecutive crashes for a given task. If a task's worker crashes more than crashes_max times in a row, then pop() throws an error when it tries to return the results of the task.

backup

An optional crew controller object, or NULL to omit. If supplied, the backup controller runs any pushed tasks that have already reached crashes_max consecutive crashes. Using backup, you can create a chain of controllers with different levels of resources (such as worker memory and CPUs) so that a task that fails on one controller can retry using incrementally more powerful workers. All controllers in a backup chain should be part of the same controller group (see crew_controller_group()) so you can call the group-level pop() and collect() methods to make sure you get results regardless of which controller actually ended up running the task.

Limitations of backup: * crashes_max needs to be positive in order for backup to be used. Otherwise, every task would always skip the current controller and go to backup. * backup cannot be a controller group. It must be an ordinary controller.

auto_scale

Deprecated. Use the scale argument of push(), pop(), and wait() instead.

See also

Other controller: crew_class_controller

Examples

if (identical(Sys.getenv("CREW_EXAMPLES"), "true")) {
client <- crew_client()
launcher <- crew_launcher_local()
controller <- crew_controller(client = client, launcher = launcher)
controller$start()
controller$push(name = "task", command = sqrt(4))
controller$wait()
controller$pop()
controller$terminate()
}