static final VarHandle valueUpdater;

    static {
      MethodHandles.Lookup lookup = MethodHandles.lookup();
      try {
        waiterThreadUpdater = lookup.findVarHandle(Waiter.class, "thread", Thread.class);
        waiterNextUpdater = lookup.findVarHandle(Waiter.class, "next", Waiter.class);
        waitersUpdater =
            lookup.findVarHandle(AbstractFutureState.class, "waitersField", Waiter.class);

        // Test deeply nested exception causes
        Exception level3 = new Exception("Level 3: Database connection failed");
        Exception level2 = new Exception("Level 2: User lookup failed", level3);
        Exception level1 = new Exception("Level 1: Authentication service error", level2);
        SsoProcessException topLevel = new SsoProcessException("SSO process failed", level1);

      return o;
    }

    @Override
    public String toString() {
      return "Functions.identity()";
    }
  }

  /**
   * Returns a function which performs a map lookup. The returned function throws an {@link
   * IllegalArgumentException} if given a key that does not exist in the map. See also {@link
   * #forMap(Map, Object)}, which returns a default value in this case.
   *

                removeWaiter(node);
                break long_wait_loop; // jump down to the busy wait loop
              }
            }
          }
          oldHead = waitersField; // re-read and loop.
        } while (oldHead != Waiter.TOMBSTONE);
      }
      // re-read valueField, if we get here then we must have observed a TOMBSTONE while trying to

         * than a handful of exceptions. But it seems prudent to set a cap on how many we'll cache.
         * This avoids out-of-control memory consumption, and it keeps the cache from growing so
         * large that doing the lookup is noticeably slower than redoing the work would be.
         *
         * Ideally we'd have a real eviction policy, but until we see a problem in practice, I hope

        scriptEngineFactory.add("name1", engine1);
        scriptEngineFactory.add("name2", engine2);

        // Both engines have same class name, so second should replace first for class name lookup
        ScriptEngine retrievedByClass = scriptEngineFactory.getScriptEngine("testscriptengine");
        assertEquals(engine2, retrievedByClass);

        // But original names should still work

         * than a handful of exceptions. But it seems prudent to set a cap on how many we'll cache.
         * This avoids out-of-control memory consumption, and it keeps the cache from growing so
         * large that doing the lookup is noticeably slower than redoing the work would be.
         *
         * Ideally we'd have a real eviction policy, but until we see a problem in practice, I hope

    public void test_getDataStore_nullName() {
        DataStore retrieved = dataStoreFactory.getDataStore(null);
        assertNull(retrieved);
    }

    // Test getDataStore with case insensitive lookup
    public void test_getDataStore_caseInsensitive() {
        TestDataStore dataStore = new TestDataStore("TestStore");
        dataStoreFactory.add("MyStore", dataStore);

   * by applying the given {@code AsyncFunction} to the result of the original {@code Future}.
   * Example usage:
   *
   * {@snippet :
   * FluentFuture<RowKey> rowKeyFuture = FluentFuture.from(indexService.lookUp(query));
   * ListenableFuture<QueryResult> queryFuture =
   *     rowKeyFuture.transformAsync(dataService::readFuture, executor);
   * }
   *

   * by applying the given {@code AsyncFunction} to the result of the original {@code Future}.
   * Example usage:
   *
   * {@snippet :
   * ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
   * ListenableFuture<QueryResult> queryFuture =
   *     transformAsync(rowKeyFuture, dataService::readFuture, executor);
   * }
   *