Asynchronous workers and tasks


_ <- fat.async


The async library introduces two types: Worker and Task


The Worker is a simple wrapper around an asynchronous operation.


Name Signature Brief
Worker (task: Method) Builds a Worker in standby mode

Prototype members

Name Signature Brief
start (): Worker Begins the task
cancel (): Void Cancels the task
await (): Worker Waits for task completion
isDone (): Boolean Checks if the task has completed
hasStarted Boolean Set by start method
hasAwaited Boolean Set by await method
isCanceled Boolean Set by cancel method
result Any Set by await method


A Task represents a time-constrained asynchronous operation. It uses two Workers, one for the task itself and another for the timeout timer.


Name Signature Brief
Task (task: Method, wait: Number) Builds a Task in standby mode

The Task constructor takes two arguments:

  • task: The method to be executed asynchronously (the method may not take arguments directly, but you may curry those in using two arrows on the definition -> ->).
  • wait (optional): The timeout in milliseconds. If the task does not finish within this time, it is cancelled. The default is 40,000ms (40 seconds).

Prototype members

Name Signature Brief
start (): Task Begins the task and its timer
cancel (): Void Cancels the task and its timer
await (): Task Waits for task completion or timeout
isDone Boolean Set true if task has been completed
hasTimedOut Boolean Set true if task timed out
result Any Set by await method

Standalone Method

Name Signature Brief
selfCancel (): * Terminates the execution of the thread

Usage Notes

Worker instances are mapped to system threads on a one-to-one basis and get executed as per the system's scheduling. This implies that their execution may not always be immediate. To wait for the result of a Worker or Task, employ the await method.


_    <- fat.async
math <- fat.math
time <- fat.time

# Define a slow task
slowTask = -> {
  waitTime = math.random * 5000  # Wait up to 5 seconds

# Start the task as a Worker
worker = Worker(slowTask).start

# Get the worker result
result1 = worker.await.result  # blocks until task is done

# Start a task with timeout
task = Task(slowTask, 3000).start

# Get the task result
result2 = task.await.result  # blocks until task is done or timeout occurs

the Task's await method will raise AsyncError if the task times out before completion

See also

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