@Test
    public void test_promiseChaining_returnsSamePromise() throws Exception {
        final Deferred<SuggestResponse> deferred = new Deferred<>();

        Deferred<SuggestResponse>.Promise promise1 = deferred.promise();
        Deferred<SuggestResponse>.Promise promise2 = promise1.then(response -> {});
        Deferred<SuggestResponse>.Promise promise3 = promise2.error(error -> {});

     */
    public Deferred<T>.Promise execute(final Client client) {
        final String error = getValidationError();
        if (!Strings.isNullOrEmpty(error)) {
            throw new IllegalArgumentException(error);
        }

        final Deferred<T> deferred = new Deferred<>();
        try {
            processRequest(client, deferred);
        } catch (final Exception e) {

     * @return A Promise that will be resolved with the SuggestIndexResponse
     */
    public Deferred<SuggestIndexResponse>.Promise indexFromQueryLog(final ContentIndexingContext ctx, final QueryLogReader queryLogReader,
            final int docPerReq, final long requestInterval) {
        final Deferred<SuggestIndexResponse> deferred = new Deferred<>();
        threadPool.execute(() -> {
            final long start = System.currentTimeMillis();

                    deferred.reject(new SuggesterException("Search failure. Failed shards num:" + searchResponse.getFailedShards()));
                } else {
                    deferred.resolve(createResponse(searchResponse));
                }
            }

            @Override
            public void onFailure(final Exception e) {
                deferred.reject(new SuggesterException(e.getMessage(), e));

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

import org.codelibs.fess.suggest.Suggester;
import org.codelibs.fess.suggest.concurrent.Deferred;
import org.codelibs.fess.suggest.constants.SuggestConstants;
import org.codelibs.fess.suggest.entity.SuggestItem;
import org.codelibs.fess.suggest.exception.SuggestIndexException;

// goroutine. When a function F calls panic, normal execution of F stops
// immediately. Any functions whose execution was deferred by F are run in
// the usual way, and then F returns to its caller. To the caller G, the
// invocation of F then behaves like a call to panic, terminating G's
// execution and running any deferred functions. This continues until all
// functions in the executing goroutine have stopped, in reverse order. At

├── concurrent/                 # Async patterns (Deferred/Promise)
└── util/                      # Utilities
```

### Key Design Patterns

- **Builder**: SuggesterBuilder, SuggestRequestBuilder
- **Facade**: Suggester (main entry point)
- **Composite**: NormalizerChain, ReadingConverterChain
- **Strategy**: Normalizer, ReadingConverter, ContentsParser
- **Deferred/Promise**: Async operations

### Index Alias Strategy

  fun addPlan(): FakePlan =
    FakePlan(nextPlanId++).also {
      plans += it
    }

  override fun isCanceled() = canceled

  override fun plan(): FakePlan {
    // Return deferred plans preferentially. These don't require addPlan().
    if (deferredPlans.isNotEmpty()) return deferredPlans.removeFirst() as FakePlan

    if (nextPlanIndex >= plans.size && autoGeneratePlans) addPlan()

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.codelibs.core.lang.StringUtil;
import org.codelibs.fess.suggest.analysis.SuggestAnalyzer;
import org.codelibs.fess.suggest.concurrent.Deferred;
import org.codelibs.fess.suggest.converter.ReadingConverter;
import org.codelibs.fess.suggest.entity.ElevateWord;
import org.codelibs.fess.suggest.entity.SuggestItem;

          } else {
            firstException.addSuppressed(throwable)
          }
        }

        val nextPlan = connectResult.nextPlan
        if (nextPlan != null) {
          // Try this plan's successor before deferred plans because it won the race!
          routePlanner.deferredPlans.addFirst(nextPlan)
        }
      }
    } finally {
      cancelInFlightConnects()
    }

    throw firstException!!
  }