mtumilowicz/java11-completable-future-timeout

Three approaches to timeouts when using CompletableFuture.

java11-completable-future-timeout

Reference: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/CompletableFuture.html

preview

We have three approaches to timeouts when using CompletableFuture:

1. public T get(long timeout, TimeUnit unit) - Waits if necessary for at most the given time for this future to complete, and then returns its result, if available.
2. CompletableFuture<T> orTimeout​(long timeout, TimeUnit unit) - Exceptionally completes this CompletableFuture with a TimeoutException if not otherwise completed before the given timeout.
3. CompletableFuture<T> completeOnTimeout​(T value, long timeout, TimeUnit unit) - Completes this CompletableFuture with the given value if not otherwise completed before the given timeout.

tests

Note that 2. and 3. are better approaches because physically no exception is thrown.

• get

  @Test(expected = TimeoutException.class)
  public void get_withTimeoutException() throws InterruptedException, ExecutionException, TimeoutException {
      var future = CompletableFuture.supplyAsync(() -> {
          Delay.delay();
          return "future";
      });
  
      future.get(100, TimeUnit.MILLISECONDS);
  }
  
  @Test
  public void get_withoutTimeoutException() throws InterruptedException, ExecutionException, TimeoutException {
      var future = CompletableFuture.supplyAsync(() -> "future");
  
      assertThat(future.get(500, TimeUnit.MILLISECONDS), is("future"));
  }
  

• orTimeout

  @Test
  public void orTimeout_withTimeoutException() {
      var future = CompletableFuture.supplyAsync(() -> {
          Delay.delay();
          return "future";
      }).orTimeout(300, TimeUnit.MILLISECONDS);
      
      Delay.delay();
      
      assertTrue(future.isCompletedExceptionally());
  }
  
  @Test
  public void orTimeout_withoutTimeoutException() {
      var future = CompletableFuture.supplyAsync(() -> "future")
              .orTimeout(300, TimeUnit.MILLISECONDS);
  
      assertThat(future.join(), is("future"));
  }
  

• completeOnTimeout​

  @Test
  public void completeOnTimeout_withTimeoutException() {
      var future = CompletableFuture.supplyAsync(() -> {
          Delay.delay();
          return "future";
      }).completeOnTimeout("timeout", 300, TimeUnit.MILLISECONDS);
  
      assertThat(future.join(), is("timeout"));
  }
  
  @Test
  public void completeOnTimeout_withoutTimeoutException() {
      var future = CompletableFuture.supplyAsync(() -> "future")
              .completeOnTimeout("timeout", 300, TimeUnit.MILLISECONDS);
  
      assertThat(future.join(), is("future"));
  }