if (lookup == null) {
            return customLifecycles != null ? customLifecycles : new HashMap<>();
        }

        // Lifecycles cannot be cached as extensions might add custom lifecycles later in the execution.
        try {
            return registry != null
                    ? registry.stream().collect(Collectors.toMap(lf -> lf.id(), lf -> new Lifecycle(registry, lf)))

        } else {
          /* Someone beat us to it! Trying again...
           *
           * Technically this loop not guaranteed to terminate, so theoretically (extremely
           * unlikely) this thread might starve, but even then, there is always going to be another
           * thread doing progress here.
           */
        }
      }
    }
  }

  /**

    // Test that listeners added both before and after the value is available
    // get called correctly.
    for (int i = 0; i < 20; i++) {

      // Right in the middle start up a thread to close the latch.
      if (i == 10) {
        new Thread(() -> latch.countDown()).start();
      }

      future.addListener(listenerLatch::countDown, exec);
    }

 * </blockquote>
 *
 *  * The hostname of this machine is <code>JMORRIS2</code>. It is
 * a member of the group(a.k.a workgroup and domain) <code>BILLING-NY</code>. To
 * obtain an {@link java.net.InetAddress} for a host one might do:
 *
 * <pre>
 *
 * InetAddress addr = NbtAddress.getByName("jmorris2").getInetAddress();
 * </pre>
 *
 *  * From a UNIX platform with Samba installed you can perform similar

This includes, for example:

* Email notifications sent after performing an action:
    * As connecting to an email server and sending an email tends to be "slow" (several seconds), you can return the response right away and send the email notification in the background.
* Processing data:

   * Returns the current sum. The returned value is NOT an atomic snapshot; invocation in
   * the absence of concurrent updates returns an accurate result, but concurrent updates that occur
   * while the sum is being calculated might not be incorporated.
   *
   * @return the sum
   */
  @Override
  public long sum() {
    long sum = base;
    Cell[] as = cells;
    if (as != null) {
      int n = as.length;

          canUseHeaderValue = false
        } else {
          headerValue = value
        }
      }
      name.equals("Pragma", ignoreCase = true) -> {
        // Might specify additional cache-control params. We invalidate just in case.
        canUseHeaderValue = false
      }
      else -> {
        continue@loop
      }
    }

    var pos = 0

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

## Use cases { #use-cases }

Some use cases include:

            }

            startLatch.countDown();
            executor.shutdown();
            assertTrue(executor.awaitTermination(5, TimeUnit.SECONDS));

            // Some operations might succeed before key wipe, some might fail after
            // At minimum, we expect some activity (not all operations should be no-ops)
            int totalOperations = successCount.get() + failureCount.get();

            //
            // We promise this because, once we cancel that Future, we would no longer be able to
            // tell when any underlying work it is doing is done. Thus, we might start a new task
            // while that underlying work is still running.
            //
            // So that is why we cancel only in the case of CAS success.
            taskFuture.cancel(false);
          }