async-execution.md

layout	title
default	Async Execution

Async Execution

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In addition to synchronous execution, Failsafe provides several ways to perform asynchronous executions or integrate with async code.

Simple Async Execution

Async executions can be performed by using the [runAsync] or [getAsync] methods, which return a [CompletableFuture]:

CompletableFuture<Connection> future = Failsafe.with(retryPolicy).getAsync(this::connect);

CompletionStage Integration

Code that returns a [CompletionStage] can be integrated with Failsafe by using the [getStageAsync] method, which accepts a [CompletionStage][CompletionStage] [Supplier][Supplier] and returns a new [CompletableFuture] with failure handling built-in:

Failsafe.with(retryPolicy)
  .getStageAsync(this::connectAsync)
  .thenAccept(System.out::println));

Async Integration

Failsafe can also integrate with threads that are outside of its control. The [runAsyncExecution] and [getAsyncExecution] methods provide an [AsyncExecution] object that can be used to record execution results from another thread:

Failsafe.with(retryPolicy).getAsyncExecution(execution -> {
  // A method that runs in a different thread
  service.connectAsync().whenComplete((connection, exception) -> {
    execution.record(connection, exception);
  });
});

The execution will be retried, if needed, when a result or exception is recorded.

ExecutorService Configuration

By default, Failsafe performs async executions using the [ForkJoinPool]'s [common pool][common-pool], but you can also configure a specific [ScheduledExecutorService] or [ExecutorService]:

Failsafe.with(policy).with(executorService).getAsync(this::connect);

Custom Schedulers

Failsafe can integrate with libraries that use their own schedulers for async executions, such as Akka or Vert.x, by supporting a custom [Scheduler]:

Failsafe.with(policy).with(akkaScheduler).getAsync(this::connect);

See the [Vert.x example][vertx-example] of a custom scheduler implementation.

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