content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.cassandra.concurrent;
  
  import accord.utils.Invariants;
  import org.apache.cassandra.utils.Closeable;
  import org.apache.cassandra.utils.WithResources;
  import org.apache.cassandra.utils.concurrent.Future;
  
  import java.util.ArrayDeque;
  import java.util.Collections;
  import java.util.List;
  import java.util.Queue;
  import java.util.concurrent.Callable;
  import java.util.concurrent.TimeUnit;
  
  public class ManualExecutor implements ExecutorPlus
  {
      private final Queue<Task> tasks = new ArrayDeque<>();
      private int completedCount = 0;
  
      public void runOne()
      {
          Task task = tasks.remove();
          task.run();
          completedCount++;
      }
  
      public void runAll()
      {
          while (!tasks.isEmpty())
              runOne();
      }
  
      @Override
      public <T> Future<T> submit(Callable<T> callable)
      {
          return submit((WithResources) null, callable);
      }
  
      @Override
      public <T> Future<T> submit(WithResources withResources, Callable<T> callable)
      {
          FutureImpl<T> future = new FutureImpl<>();
          tasks.add(new Task(null, callable, withResources, null, future));
          return future;
      }
  
      @Override
      public Future<?> submit(Runnable runnable)
      {
          return submit(null, runnable, null);
      }
  
      @Override
      public Future<?> submit(WithResources withResources, Runnable runnable)
      {
          return submit(withResources, runnable, null);
      }
  
      @Override
      public <T> Future<T> submit(Runnable runnable, T result)
      {
          return submit(null, runnable, result);
      }
  
      @Override
      public <T> Future<T> submit(WithResources withResources, Runnable runnable, T result)
      {
          FutureImpl<T> future = new FutureImpl<>();
          tasks.add(new Task(runnable, null, withResources, result, future));
          return future;
      }
  
      @Override
      public void execute(Runnable runnable)
      {
          execute(null, runnable);
      }
  
      @Override
      public void execute(WithResources withResources, Runnable runnable)
      {
          tasks.add(new Task(runnable, null, withResources, null, null));
      }
  
      private static class Task
      {
          private final Runnable runnable;
          private final Callable<?> callable;
          private final WithResources withResources;
          private final FutureImpl<?> future;
  
          private Object result;
  
          Task(Runnable runnable, Callable<?> callable, WithResources withResources, Object result, FutureImpl<?> future)
          {
              Invariants.requireArgument(runnable != null ^ callable != null);
  
              this.runnable = runnable;
              this.callable = callable;
              this.withResources = withResources;
              this.result = result;
              this.future = future;
          }
  
          void run()
          {
              try (Closeable ignored = withResources == null ? null : withResources.get())
              {
                  if (null != runnable)
                      runnable.run();
                  else
                      result = callable.call();
  
                  if (null != future)
                      future.succeed(result);
              }
              catch (Throwable t)
              {
                  ExecutionFailure.handle(t);
                  if (null != future)
                      future.fail(t);
              }
          }
      }
  
      private static class FutureImpl<V> extends org.apache.cassandra.utils.concurrent.AsyncFuture<V>
      {
          @SuppressWarnings("unchecked")
          void succeed(Object v)
          {
              trySuccess((V) v);
          }
  
          void fail(Throwable throwable)
          {
              tryFailure(throwable);
          }
      }
  
      @Override
      public boolean inExecutor()
      {
          return true;
      }
  
      @Override public int  getActiveTaskCount()    { return 0; }
      @Override public long getCompletedTaskCount() { return completedCount; }
      @Override public int  getPendingTaskCount()   { return tasks.size(); }
  
      @Override public int  getCorePoolSize()       { return 0; }
      @Override public int  getMaximumPoolSize()    { return 0; }
      @Override public void setCorePoolSize(int newCorePoolSize)       { throw new IllegalArgumentException("Cannot resize ManualExecutor"); }
      @Override public void setMaximumPoolSize(int newMaximumPoolSize) { throw new IllegalArgumentException("Cannot resize ManualExecutor"); }
  
      @Override public void shutdown() {}
      @Override public List<Runnable> shutdownNow() { return Collections.emptyList(); }
      @Override public boolean isShutdown()   { return false; }
      @Override public boolean isTerminated() { return false; }
      @Override public boolean awaitTermination(long timeout, TimeUnit unit) { return true; }
  }
  