// Execute concurrently
crawler1.setBackground(true);
crawler2.setBackground(true);

String sessionId1 = crawler1.execute();
String sessionId2 = crawler2.execute();

crawler1.awaitTermination();
crawler2.awaitTermination();
```

### Custom Interval Control

```java
// Configure politeness policy
container.singleton("intervalController", DefaultIntervalController.class, controller -> {

    public boolean isShutdown() {
      return shutdown;
    }

    @Override
    public boolean isTerminated() {
      return shutdown;
    }

    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit) {
      return true;
    }

    @Override
    public void execute(Runnable runnable) {}

    @Override
    public <V> ListenableScheduledFuture<V> schedule(

      throw new UnsupportedOperationException();
    }

    @Override
    public boolean isTerminated() {
      throw new UnsupportedOperationException();
    }

    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit) {
      throw new UnsupportedOperationException();
    }
  }

  private static class ImmediateScheduledFuture<V> extends SimpleForwardingListenableFuture<V>

        };

    service.startAsync();
    assertFalse(service.executor().isShutdown());
    service.awaitRunning();
    service.stopAsync();
    service.awaitTerminated();
    assertTrue(executor.get().awaitTermination(100, MILLISECONDS));
  }

  public void testDefaultExecutorIsShutdownWhenServiceFails() throws Exception {
    AtomicReference<ScheduledExecutorService> executor = Atomics.newReference();

        };

    service.startAsync();
    assertFalse(service.executor().isShutdown());
    service.awaitRunning();
    service.stopAsync();
    service.awaitTerminated();
    assertTrue(executor.get().awaitTermination(100, MILLISECONDS));
  }

  public void testDefaultExecutorIsShutdownWhenServiceFails() throws Exception {
    AtomicReference<ScheduledExecutorService> executor = Atomics.newReference();

      lastDelay = delay;
      lastUnit = unit;
      return null;
    }

    // No need to test these methods as they are handled by WrappingExecutorServiceTest
    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit) {
      throw new UnsupportedOperationException();
    }

    @Override
    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)

      lastDelay = delay;
      lastUnit = unit;
      return null;
    }

    // No need to test these methods as they are handled by WrappingExecutorServiceTest
    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit) {
      throw new UnsupportedOperationException();
    }

    @Override
    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)

    public boolean isShutdown() {
      return shutdown;
    }

    @Override
    public boolean isTerminated() {
      return shutdown;
    }

    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit) {
      return true;
    }

    @Override
    public void execute(Runnable runnable) {}

    @Override
    public <V> ListenableScheduledFuture<V> schedule(

                while (!at.compareAndSet(2.0, 3.0)) {
                  Thread.yield();
                }
              }
            });

    assertTrue(at.compareAndSet(1.0, 2.0));
    awaitTermination(t);
    assertBitEquals(3.0, at.get());
  }

  /** repeated weakCompareAndSet succeeds in changing value when equal to expected */
  public void testWeakCompareAndSet() {
    double prev = Math.E;

                while (!at.compareAndSet(2.0, 3.0)) {
                  Thread.yield();
                }
              }
            });

    assertTrue(at.compareAndSet(1.0, 2.0));
    awaitTermination(t);
    assertBitEquals(3.0, at.get());
  }

  /** repeated weakCompareAndSet succeeds in changing value when equal to expected */
  public void testWeakCompareAndSet() {
    double prev = Math.E;