/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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.netty.util.concurrent;
  
  import io.netty.util.concurrent.AutoScalingEventExecutorChooserFactory.AutoScalingUtilizationMetric;
  import io.netty.util.concurrent.EventExecutorChooserFactory.ObservableEventExecutorChooser;
  
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.concurrent.Executor;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  
  /**
   * Abstract base class for {@link EventExecutorGroup} implementations that handles their tasks with multiple threads at
   * the same time.
   */
  public abstract class MultithreadEventExecutorGroup extends AbstractEventExecutorGroup {
  
      private final EventExecutor[] children;
      private final Set<EventExecutor> readonlyChildren;
      private final AtomicInteger terminatedChildren = new AtomicInteger();
      private final Promise<?> terminationFuture = new DefaultPromise(GlobalEventExecutor.INSTANCE);
      private final EventExecutorChooserFactory.EventExecutorChooser chooser;
  
      /**
       * Create a new instance.
       *
       * @param nThreads          the number of threads that will be used by this instance.
       * @param threadFactory     the ThreadFactory to use, or {@code null} if the default should be used.
       * @param args              arguments which will passed to each {@link #newChild(Executor, Object...)} call
       */
      protected MultithreadEventExecutorGroup(int nThreads, ThreadFactory threadFactory, Object... args) {
          this(nThreads, threadFactory == null ? null : new ThreadPerTaskExecutor(threadFactory), args);
      }
  
      /**
       * Create a new instance.
       *
       * @param nThreads          the number of threads that will be used by this instance.
       * @param executor          the Executor to use, or {@code null} if the default should be used.
       * @param args              arguments which will passed to each {@link #newChild(Executor, Object...)} call
       */
      protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {
          this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);
      }
  
      /**
       * Create a new instance.
       *
       * @param nThreads          the number of threads that will be used by this instance.
       * @param executor          the Executor to use, or {@code null} if the default should be used.
       * @param chooserFactory    the {@link EventExecutorChooserFactory} to use.
       * @param args              arguments which will passed to each {@link #newChild(Executor, Object...)} call
       */
      protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
                                              EventExecutorChooserFactory chooserFactory, Object... args) {
          checkPositive(nThreads, "nThreads");
  
          if (executor == null) {
              executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
          }
  
          children = new EventExecutor[nThreads];
  
          for (int i = 0; i < nThreads; i ++) {
              boolean success = false;
              try {
                  children[i] = newChild(executor, args);
                  success = true;
              } catch (Exception e) {
                  // TODO: Think about if this is a good exception type
                  throw new IllegalStateException("failed to create a child event loop", e);
              } finally {
                  if (!success) {
                      for (int j = 0; j < i; j ++) {
                          children[j].shutdownGracefully();
                      }
  
                      for (int j = 0; j < i; j ++) {
                         EventExecutor e = children[j];
                         try {
                             while (!e.isTerminated()) {
                                 e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
                             }
                         } catch (InterruptedException interrupted) {
                             // Let the caller handle the interruption.
                             Thread.currentThread().interrupt();
                             break;
                         }
                     }
                 }
             }
         }
 
         chooser = chooserFactory.newChooser(children);
 
         final FutureListener<Object> terminationListener = future -> {
             if (terminatedChildren.incrementAndGet() == children.length) {
                 terminationFuture.setSuccess(null);
             }
         };
 
         for (EventExecutor e: children) {
             e.terminationFuture().addListener(terminationListener);
         }
 
         Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
         Collections.addAll(childrenSet, children);
         readonlyChildren = Collections.unmodifiableSet(childrenSet);
     }
 
     protected ThreadFactory newDefaultThreadFactory() {
         return new DefaultThreadFactory(getClass());
     }
 
     @Override
     public EventExecutor next() {
         return chooser.next();
     }
 
     @Override
     public Iterator<EventExecutor> iterator() {
         return readonlyChildren.iterator();
     }
 
     /**
      * Return the number of {@link EventExecutor} this implementation uses. This number is the maps
      * 1:1 to the threads it use.
      */
     public final int executorCount() {
         return children.length;
     }
 
     /**
      * Returns the number of currently active threads if the group is using an
      * {@link ObservableEventExecutorChooser}. Otherwise, for a non-scaling group,
      * this method returns the total number of threads, as all are considered active.
      *
      * @return the count of active threads.
      */
     public int activeExecutorCount() {
         if (chooser instanceof ObservableEventExecutorChooser) {
             return ((ObservableEventExecutorChooser) chooser).activeExecutorCount();
         }
         return executorCount();
     }
 
     /**
      * Returns a list of real-time utilization metrics if the group was configured
      * with a compatible {@link EventExecutorChooserFactory}, otherwise an empty list.
      *
      * @return A list of {@link AutoScalingUtilizationMetric} objects.
      */
     public List<AutoScalingUtilizationMetric> executorUtilizations() {
         if (chooser instanceof ObservableEventExecutorChooser) {
             return ((ObservableEventExecutorChooser) chooser).executorUtilizations();
         }
         return Collections.emptyList();
     }
 
     /**
      * Create a new EventExecutor which will later then accessible via the {@link #next()}  method. This method will be
      * called for each thread that will serve this {@link MultithreadEventExecutorGroup}.
      *
      */
     protected abstract EventExecutor newChild(Executor executor, Object... args) throws Exception;
 
     @Override
     public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
         for (EventExecutor l: children) {
             l.shutdownGracefully(quietPeriod, timeout, unit);
         }
         return terminationFuture();
     }
 
     @Override
     public Future<?> terminationFuture() {
         return terminationFuture;
     }
 
     @Override
     @Deprecated
     public void shutdown() {
         for (EventExecutor l: children) {
             l.shutdown();
         }
     }
 
     @Override
     public boolean isShuttingDown() {
         for (EventExecutor l: children) {
             if (!l.isShuttingDown()) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     public boolean isShutdown() {
         for (EventExecutor l: children) {
             if (!l.isShutdown()) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     public boolean isTerminated() {
         for (EventExecutor l: children) {
             if (!l.isTerminated()) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     public boolean awaitTermination(long timeout, TimeUnit unit)
             throws InterruptedException {
         long deadline = System.nanoTime() + unit.toNanos(timeout);
         loop: for (EventExecutor l: children) {
             for (;;) {
                 long timeLeft = deadline - System.nanoTime();
                 if (timeLeft <= 0) {
                     break loop;
                 }
                 if (l.awaitTermination(timeLeft, TimeUnit.NANOSECONDS)) {
                     break;
                 }
             }
         }
         return isTerminated();
     }
 }