nd Dart ](https://dart.dev/articles/event-loop/) : Learn how Dart handles the event queue and microtask queue, so you can write better asynchronous code with fewer surprises. 

  * [ test package: Asynchronous Tests ](https://pub.dev/packages/test) : How to test asynchronous code. 

##  Classes

[ Completer ](dart-async/Completer-class.html) < T  >

     A way to produce Future objects and to complete them later with a value or error. 
[ EventSink ](dart-async/EventSink-class.html) < T  >

     A [ Sink ](dart-core/Sink-class.html) that supports adding errors. 
[ Future ](dart-async/Future-class.html) < T  >

     The result of an asynchronous computation. 
[ FutureOr ](dart-async/FutureOr-class.html) < T  >

     A type representing values that are either ` Future<T> ` or ` T ` . 
[ MultiStreamController ](dart-async/MultiStreamController-class.html) < T  >

     An enhanced stream controller provided by [ Stream.multi ](dart-async/Stream/Stream.multi.html) . 
[ Stream ](dart-async/Stream-class.html) < T  >

     A source of asynchronous data events. 
[ StreamConsumer ](dart-async/StreamConsumer-class.html) < S  >

     Abstract interface for a "sink" accepting multiple entire streams. 
[ StreamController ](dart-async/StreamController-class.html) < T  >

     A controller with the stream it controls. 
[ StreamIterator ](dart-async/StreamIterator-class.html) < T  >

     An [ Iterator ](dart-core/Iterator-class.html) -like interface for the values of a [ Stream ](dart-async/Stream-class.html) . 
[ StreamSink ](dart-async/StreamSink-class.html) < S  >

     A object that accepts stream events both synchronously and asynchronously. 
[ StreamSubscription ](dart-async/StreamSubscription-class.html) < T  >

     A subscription on events from a [ Stream ](dart-async/Stream-class.html) . 
[ StreamTransformer ](dart-async/StreamTransformer-class.html) < S  ,  T  >

     Transforms a Stream. 
[ StreamTransformerBase ](dart-async/StreamTransformerBase-class.html) < S  ,
T  >

     Base class for implementing [ StreamTransformer ](dart-async/StreamTransformer-class.html) . 
[ StreamView ](dart-async/StreamView-class.html) < T  >

     [ Stream ](dart-async/Stream-class.html) wrapper that only exposes the [ Stream ](dart-async/Stream-class.html) interface. 
[ SynchronousStreamController ](dart-async/SynchronousStreamController-
class.html) < T  >

     A stream controller that delivers its events synchronously. 
[ Timer ](dart-async/Timer-class.html)

     A countdown timer that can be configured to fire once or repeatedly. 
[ Zone ](dart-async/Zone-class.html)

     A zone represents an environment that remains stable across asynchronous calls. 
[ ZoneDelegate ](dart-async/ZoneDelegate-class.html)

     An adapted view of the parent zone. 
[ ZoneSpecification ](dart-async/ZoneSpecification-class.html)

     A parameter object with custom zone function handlers for [ Zone.fork ](dart-async/Zone/fork.html) . 

##  Extensions

[ FutureExtensions ](dart-async/FutureExtensions.html)

     Convenience methods on futures. 
[ FutureIterable ](dart-async/FutureIterable.html)

    
[ FutureRecord2 ](dart-async/FutureRecord2.html)

     Parallel operations on a record of futures. 
[ FutureRecord3 ](dart-async/FutureRecord3.html)

     Parallel operations on a record of futures. 
[ FutureRecord4 ](dart-async/FutureRecord4.html)

     Parallel operations on a record of futures. 
[ FutureRecord5 ](dart-async/FutureRecord5.html)

     Parallel operations on a record of futures. 
[ FutureRecord6 ](dart-async/FutureRecord6.html)

     Parallel operations on a record of futures. 
[ FutureRecord7 ](dart-async/FutureRecord7.html)

     Parallel operations on a record of futures. 
[ FutureRecord8 ](dart-async/FutureRecord8.html)

     Parallel operations on a record of futures. 
[ FutureRecord9 ](dart-async/FutureRecord9.html)

     Parallel operations on a record of futures. 

##  Functions

[ runZoned ](dart-async/runZoned.html) < R  > (  R  body  (),  {