Async Execution

1. Simple Async Execution
2. CompletionStage Integration
3. Async Integration
4. ExecutorService Configuration
5. Custom Schedulers

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 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, 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 of a custom scheduler implementation.