code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.schedulers;
  
  import java.util.concurrent.TimeUnit;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.Scheduler;
  import io.reactivex.rxjava3.disposables.*;
  
  /**
   * A Scheduler partially implementing the API by allowing only non-delayed, non-periodic
   * task execution on the current thread immediately.
   * <p>
   * Note that this doesn't support recursive scheduling and disposing the returned Disposable
   * has no effect (because when the schedule() method returns, the task has been already run).
   */
  public final class ImmediateThinScheduler extends Scheduler {
  
      /**
       * The singleton instance of the immediate (thin) scheduler.
       */
      public static final Scheduler INSTANCE = new ImmediateThinScheduler();
  
      static final Worker WORKER = new ImmediateThinWorker();
  
      static final Disposable DISPOSED;
  
      static {
          DISPOSED = Disposable.empty();
          DISPOSED.dispose();
      }
  
      private ImmediateThinScheduler() {
          // singleton class
      }
  
      @NonNull
      @Override
      public Disposable scheduleDirect(@NonNull Runnable run) {
          run.run();
          return DISPOSED;
      }
  
      @NonNull
      @Override
      public Disposable scheduleDirect(@NonNull Runnable run, long delay, TimeUnit unit) {
          throw new UnsupportedOperationException("This scheduler doesn't support delayed execution");
      }
  
      @NonNull
      @Override
      public Disposable schedulePeriodicallyDirect(@NonNull Runnable run, long initialDelay, long period, TimeUnit unit) {
          throw new UnsupportedOperationException("This scheduler doesn't support periodic execution");
      }
  
      @NonNull
      @Override
      public Worker createWorker() {
          return WORKER;
      }
  
      static final class ImmediateThinWorker extends Worker {
  
          @Override
          public void dispose() {
              // This worker is always stateless and won't track tasks
          }
  
          @Override
          public boolean isDisposed() {
              return false; // dispose() has no effect
          }
  
          @NonNull
          @Override
          public Disposable schedule(@NonNull Runnable run) {
              run.run();
              return DISPOSED;
          }
  
          @NonNull
          @Override
          public Disposable schedule(@NonNull Runnable run, long delay, @NonNull TimeUnit unit) {
              throw new UnsupportedOperationException("This scheduler doesn't support delayed execution");
          }
  
          @NonNull
          @Override
          public Disposable schedulePeriodically(@NonNull Runnable run, long initialDelay, long period, TimeUnit unit) {
              throw new UnsupportedOperationException("This scheduler doesn't support periodic execution");
          }
      }
  }
  