Documentation for gololang.Async

This module offers asynchronous programming helpers, especially execution context agnostic promises and futures. The provided APIs are orthogonal to the execution strategy: it is up to you to execute code from the same thread, from a separate thread, or by pushing new tasks to a service executor.

The functions and augmentations in this module often delegate to Java classes from gololang.concurrent.async.



Bridge structure to hold a reference to a Golo future and a Java future.

Instances of this struct are being returned by the enqueue augmentation on ExecutorService instances. This essentially adds the ability to:




A set of forwarding augmentations for FutureBridge instances.

The provided functions all forward to Golo futures, while cancel forwards to a Java future.

cancel(this, mayInterruptIfRunning)

fallbackTo(this, future)

filter(this, pred)

flatMap(this, fun)

map(this, fun)

onFail(this, listener)

onSet(this, listener)


Augmentation on the base Future objects provided by the gololang.concurrent.async.Future Java class.

fallbackTo(this, future)

Returns a fallback future:

filter(this, pred)

Returns a future that filters this future through the pred predicate function.

Suppose that this future is set to v:

If this future fails, so does the returned future.

flatMap(this, fun)

Similar to map, except that fun returns a future, not a value.

map(this, fun)

Returns a future whose value is mapped through the fun function.

If this future is set to v, then the returned future is set to fun(v). If it fails, the returned future is also failed with the same exception.


Augmentation on the base Promise objects provided by the gololang.concurrent.async.Promise Java class.

The promise initialize method takes one argument, a callback with two parameters, resolve and reject. Do something within the callback, then call resolve if everything worked, otherwise call reject:

let myPromise = -> promise(): initialize(|resolve, reject| {
  if everythingTurnedOutFine is true {
    resolve("Stuff worked!")
  } else {

  : onSet(|result| {
      println(result) # Stuff worked!
  : onFail(|err| {
      println(err: getMessage()) # Failed!

initialize(this, closure)

initializeWithinThread(this, closure)

You can define a promise which runs “stuff” inside a Thread


Augmentations for ExecutorService.

enqueue(this, fun)

Submits a function fun to be executed by this scheduler, and returns a FutureBridge.

fun takes no parameters, and its return value is used as a future value.

The returned FutureBridge` behaves both as a composable Golo future and as a Java future that can be cancelled.

Here is a sample usage:

# Enqueue some elaborated work
let f = executor: enqueue({
  return 666

# Watch what could happen
f: onSet(|v| -> println(v)):
   onFail(|e| -> println(e: getMessage()))

# ...but make it fail unless the CPU was too slow
f: cancel(true)



Given a collection of futures, returns a future whose value is eventually a vector with the results of these futures.


all([ setFuture(1), failedFuture(e) ])

this yields a future whose eventual value is:

vector[1, e]

Results are accumulated as futures get resolved. The last completed future triggers the calls to onSet-registered listeners on the same thread.


Given a collection of futures, returns a future whose value is set to the first completing future.

If all futures fail, then the returned future fails to a java.util.NoSuchElementException.


Returns a failed future to a throwable exception.


Returns a new promise. Promise objects have the following useful methods.

Future objects have the following methods.

reduce(futures, init, reducer)

Returns a future whose value is set to the reduction of a collection of futures.

If any future fails, then the result future fails, too. Otherwise, the returned future is set to the accumulation of the values. Listeners callbacks get executed on the thread of the completing future which is either the last successful future or the first future to fail.


Returns a future set to value.