/*
    * 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:
    *
    *   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.netty.util.concurrent;
  
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.lang.Thread.State;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Queue;
  import java.util.Set;
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.Callable;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.LinkedBlockingQueue;
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.Semaphore;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  
  /**
   * Abstract base class for {@link OrderedEventExecutor}'s that execute all its submitted tasks in a single thread.
   *
   */
  public abstract class SingleThreadEventExecutor extends AbstractScheduledEventExecutor implements OrderedEventExecutor {
  
      static final int DEFAULT_MAX_PENDING_EXECUTOR_TASKS = Math.max(16,
              SystemPropertyUtil.getInt("io.netty.eventexecutor.maxPendingTasks", Integer.MAX_VALUE));
  
      private static final InternalLogger logger =
              InternalLoggerFactory.getInstance(SingleThreadEventExecutor.class);
  
      private static final int ST_NOT_STARTED = 1;
      private static final int ST_STARTED = 2;
      private static final int ST_SHUTTING_DOWN = 3;
      private static final int ST_SHUTDOWN = 4;
      private static final int ST_TERMINATED = 5;
  
      private static final Runnable WAKEUP_TASK = new Runnable() {
          @Override
          public void run() {
              // Do nothing.
          }
      };
  
      private static final AtomicIntegerFieldUpdater<SingleThreadEventExecutor> STATE_UPDATER =
              AtomicIntegerFieldUpdater.newUpdater(SingleThreadEventExecutor.class, "state");
  
      private final EventExecutorGroup parent;
      private final Queue<Runnable> taskQueue;
      private final Thread thread;
      private final ThreadProperties threadProperties;
      private final Semaphore threadLock = new Semaphore(0);
      private final Set<Runnable> shutdownHooks = new LinkedHashSet<Runnable>();
      private final boolean addTaskWakesUp;
      private final int maxPendingTasks;
      private final RejectedExecutionHandler rejectedExecutionHandler;
  
      private long lastExecutionTime;
  
      @SuppressWarnings({ "FieldMayBeFinal", "unused" })
      private volatile int state = ST_NOT_STARTED;
  
      private volatile long gracefulShutdownQuietPeriod;
      private volatile long gracefulShutdownTimeout;
      private long gracefulShutdownStartTime;
  
      private final Promise<?> terminationFuture = new DefaultPromise<Void>(GlobalEventExecutor.INSTANCE);
  
      /**
       * Create a new instance
       *
       * @param parent            the {@link EventExecutorGroup} which is the parent of this instance and belongs to it
       * @param threadFactory     the {@link ThreadFactory} which will be used for the used {@link Thread}
       * @param addTaskWakesUp    {@code true} if and only if invocation of {@link #addTask(Runnable)} will wake up the
       *                          executor thread
       */
      protected SingleThreadEventExecutor(
              EventExecutorGroup parent, ThreadFactory threadFactory, boolean addTaskWakesUp) {
         this(parent, threadFactory, addTaskWakesUp, DEFAULT_MAX_PENDING_EXECUTOR_TASKS,
                 RejectedExecutionHandlers.reject());
     }
 
     /**
      * Create a new instance
      *
      * @param parent            the {@link EventExecutorGroup} which is the parent of this instance and belongs to it
      * @param threadFactory     the {@link ThreadFactory} which will be used for the used {@link Thread}
      * @param addTaskWakesUp    {@code true} if and only if invocation of {@link #addTask(Runnable)} will wake up the
      *                          executor thread
      * @param maxPendingTasks   the maximum number of pending tasks before new tasks will be rejected.
      * @param rejectedHandler   the {@link RejectedExecutionHandler} to use.
      */
     @SuppressWarnings("deprecation")
     protected SingleThreadEventExecutor(
             EventExecutorGroup parent, ThreadFactory threadFactory, boolean addTaskWakesUp, int maxPendingTasks,
             RejectedExecutionHandler rejectedHandler) {
         if (threadFactory == null) {
             throw new NullPointerException("threadFactory");
         }
 
         this.parent = parent;
         this.addTaskWakesUp = addTaskWakesUp;
 
         thread = threadFactory.newThread(new Runnable() {
             @Override
             public void run() {
                 boolean success = false;
                 updateLastExecutionTime();
                 try {
                     SingleThreadEventExecutor.this.run();
                     success = true;
                 } catch (Throwable t) {
                     logger.warn("Unexpected exception from an event executor: ", t);
                 } finally {
                     for (;;) {
                         int oldState = STATE_UPDATER.get(SingleThreadEventExecutor.this);
                         if (oldState >= ST_SHUTTING_DOWN || STATE_UPDATER.compareAndSet(
                                 SingleThreadEventExecutor.this, oldState, ST_SHUTTING_DOWN)) {
                             break;
                         }
                     }
                     // Check if confirmShutdown() was called at the end of the loop.
                     if (success && gracefulShutdownStartTime == 0) {
                         logger.error(
                                 "Buggy " + EventExecutor.class.getSimpleName() + " implementation; " +
                                 SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called " +
                                 "before run() implementation terminates.");
                     }
 
                     try {
                         // Run all remaining tasks and shutdown hooks.
                         for (;;) {
                             if (confirmShutdown()) {
                                 break;
                             }
                         }
                     } finally {
                         try {
                             cleanup();
                         } finally {
                             STATE_UPDATER.set(SingleThreadEventExecutor.this, ST_TERMINATED);
                             threadLock.release();
                             if (!taskQueue.isEmpty()) {
                                 logger.warn(
                                         "An event executor terminated with " +
                                         "non-empty task queue (" + taskQueue.size() + ')');
                             }
 
                             terminationFuture.setSuccess(null);
                         }
                     }
                 }
             }
         });
         threadProperties = new DefaultThreadProperties(thread);
         this.maxPendingTasks = Math.max(16, maxPendingTasks);
         taskQueue = newTaskQueue();
         rejectedExecutionHandler = ObjectUtil.checkNotNull(rejectedHandler, "rejectedHandler");
     }
 
     /**
      * @deprecated Please use and override {@link #newTaskQueue(int)}.
      */
     @Deprecated
     protected Queue<Runnable> newTaskQueue() {
         return newTaskQueue(maxPendingTasks);
     }
 
     /**
      * Create a new {@link Queue} which will holds the tasks to execute. This default implementation will return a
      * {@link LinkedBlockingQueue} but if your sub-class of {@link SingleThreadEventExecutor} will not do any blocking
      * calls on the this {@link Queue} it may make sense to {@code @Override} this and return some more performant
      * implementation that does not support blocking operations at all.
      */
     protected Queue<Runnable> newTaskQueue(int maxPendingTasks) {
         return new LinkedBlockingQueue<Runnable>(maxPendingTasks);
     }
 
     @Override
     public EventExecutorGroup parent() {
         return parent;
     }
 
     /**
      * Interrupt the current running {@link Thread}.
      */
     protected void interruptThread() {
         thread.interrupt();
     }
 
     /**
      * @see Queue#poll()
      */
     protected Runnable pollTask() {
         assert inEventLoop();
         for (;;) {
             Runnable task = taskQueue.poll();
             if (task == WAKEUP_TASK) {
                 continue;
             }
             return task;
         }
     }
 
     /**
      * Take the next {@link Runnable} from the task queue and so will block if no task is currently present.
      * <p>
      * Be aware that this method will throw an {@link UnsupportedOperationException} if the task queue, which was
      * created via {@link #newTaskQueue()}, does not implement {@link BlockingQueue}.
      * </p>
      *
      * @return {@code null} if the executor thread has been interrupted or waken up.
      */
     protected Runnable takeTask() {
         assert inEventLoop();
         if (!(taskQueue instanceof BlockingQueue)) {
             throw new UnsupportedOperationException();
         }
 
         BlockingQueue<Runnable> taskQueue = (BlockingQueue<Runnable>) this.taskQueue;
         for (;;) {
             ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
             if (scheduledTask == null) {
                 Runnable task = null;
                 try {
                     task = taskQueue.take();
                     if (task == WAKEUP_TASK) {
                         task = null;
                     }
                 } catch (InterruptedException e) {
                     // Ignore
                 }
                 return task;
             } else {
                 long delayNanos = scheduledTask.delayNanos();
                 Runnable task = null;
                 if (delayNanos > 0) {
                     try {
                         task = taskQueue.poll(delayNanos, TimeUnit.NANOSECONDS);
                     } catch (InterruptedException e) {
                         return null;
                     }
                 }
                 if (task == null) {
                     // We need to fetch the scheduled tasks now as otherwise there may be a chance that
                     // scheduled tasks are never executed if there is always one task in the taskQueue.
                     // This is for example true for the read task of OIO Transport
                     // See https://github.com/netty/netty/issues/1614
                     fetchFromScheduledTaskQueue();
                     task = taskQueue.poll();
                 }
 
                 if (task != null) {
                     return task;
                 }
             }
         }
     }
 
     private boolean fetchFromScheduledTaskQueue() {
         long nanoTime = AbstractScheduledEventExecutor.nanoTime();
         Runnable scheduledTask  = pollScheduledTask(nanoTime);
         while (scheduledTask != null) {
             if (!taskQueue.offer(scheduledTask)) {
                 // No space left in the task queue add it back to the scheduledTaskQueue so we pick it up again.
                 scheduledTaskQueue().add((ScheduledFutureTask<?>) scheduledTask);
                 return false;
             }
             scheduledTask  = pollScheduledTask(nanoTime);
         }
         return true;
     }
 
     /**
      * @see Queue#peek()
      */
     protected Runnable peekTask() {
         assert inEventLoop();
         return taskQueue.peek();
     }
 
     /**
      * @see Queue#isEmpty()
      */
     protected boolean hasTasks() {
         assert inEventLoop();
         return !taskQueue.isEmpty();
     }
 
     /**
      * Return the number of tasks that are pending for processing.
      *
      * <strong>Be aware that this operation may be expensive as it depends on the internal implementation of the
      * SingleThreadEventExecutor. So use it was care!</strong>
      */
     public int pendingTasks() {
         return taskQueue.size();
     }
 
     /**
      * Add a task to the task queue, or throws a {@link RejectedExecutionException} if this instance was shutdown
      * before.
      */
     protected void addTask(Runnable task) {
         if (task == null) {
             throw new NullPointerException("task");
         }
         if (!offerTask(task)) {
             rejectedExecutionHandler.rejected(task, this);
         }
     }
 
     final boolean offerTask(Runnable task) {
         if (isShutdown()) {
             reject();
         }
         return taskQueue.offer(task);
     }
 
     /**
      * @see Queue#remove(Object)
      */
     protected boolean removeTask(Runnable task) {
         if (task == null) {
             throw new NullPointerException("task");
         }
         return taskQueue.remove(task);
     }
 
     /**
      * Poll all tasks from the task queue and run them via {@link Runnable#run()} method.
      *
      * @return {@code true} if and only if at least one task was run
      */
     protected boolean runAllTasks() {
         boolean fetchedAll;
         do {
             fetchedAll = fetchFromScheduledTaskQueue();
             Runnable task = pollTask();
             if (task == null) {
                 return false;
             }
 
             for (;;) {
                 try {
                     task.run();
                 } catch (Throwable t) {
                     logger.warn("A task raised an exception.", t);
                 }
 
                 task = pollTask();
                 if (task == null) {
                     break;
                 }
             }
         } while (!fetchedAll); // keep on processing until we fetched all scheduled tasks.
 
         lastExecutionTime = ScheduledFutureTask.nanoTime();
         return true;
     }
 
     /**
      * Poll all tasks from the task queue and run them via {@link Runnable#run()} method.  This method stops running
      * the tasks in the task queue and returns if it ran longer than {@code timeoutNanos}.
      */
     protected boolean runAllTasks(long timeoutNanos) {
         fetchFromScheduledTaskQueue();
         Runnable task = pollTask();
         if (task == null) {
             return false;
         }
 
         final long deadline = ScheduledFutureTask.nanoTime() + timeoutNanos;
         long runTasks = 0;
         long lastExecutionTime;
         for (;;) {
             try {
                 task.run();
             } catch (Throwable t) {
                 logger.warn("A task raised an exception.", t);
             }
 
             runTasks ++;
 
             // Check timeout every 64 tasks because nanoTime() is relatively expensive.
             // XXX: Hard-coded value - will make it configurable if it is really a problem.
             if ((runTasks & 0x3F) == 0) {
                 lastExecutionTime = ScheduledFutureTask.nanoTime();
                 if (lastExecutionTime >= deadline) {
                     break;
                 }
             }
 
             task = pollTask();
             if (task == null) {
                 lastExecutionTime = ScheduledFutureTask.nanoTime();
                 break;
             }
         }
 
         this.lastExecutionTime = lastExecutionTime;
         return true;
     }
 
     /**
      * Returns the amount of time left until the scheduled task with the closest dead line is executed.
      */
     protected long delayNanos(long currentTimeNanos) {
         ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
         if (scheduledTask == null) {
             return SCHEDULE_PURGE_INTERVAL;
         }
 
         return scheduledTask.delayNanos(currentTimeNanos);
     }
 
     /**
      * Updates the internal timestamp that tells when a submitted task was executed most recently.
      * {@link #runAllTasks()} and {@link #runAllTasks(long)} updates this timestamp automatically, and thus there's
      * usually no need to call this method.  However, if you take the tasks manually using {@link #takeTask()} or
      * {@link #pollTask()}, you have to call this method at the end of task execution loop for accurate quiet period
      * checks.
      */
     protected void updateLastExecutionTime() {
         lastExecutionTime = ScheduledFutureTask.nanoTime();
     }
 
     /**
      *
      */
     protected abstract void run();
 
     /**
      * Do nothing, sub-classes may override
      */
     protected void cleanup() {
         // NOOP
     }
 
     protected void wakeup(boolean inEventLoop) {
         if (!inEventLoop || state == ST_SHUTTING_DOWN) {
             // Use offer as we actually only need this to unblock the thread and if offer fails we do not care as there
             // is already something in the queue.
             taskQueue.offer(WAKEUP_TASK);
         }
     }
 
     @Override
     public boolean inEventLoop(Thread thread) {
         return thread == this.thread;
     }
 
     /**
      * Add a {@link Runnable} which will be executed on shutdown of this instance
      */
     public void addShutdownHook(final Runnable task) {
         if (inEventLoop()) {
             shutdownHooks.add(task);
         } else {
             execute(new Runnable() {
                 @Override
                 public void run() {
                     shutdownHooks.add(task);
                 }
             });
         }
     }
 
     /**
      * Remove a previous added {@link Runnable} as a shutdown hook
      */
     public void removeShutdownHook(final Runnable task) {
         if (inEventLoop()) {
             shutdownHooks.remove(task);
         } else {
             execute(new Runnable() {
                 @Override
                 public void run() {
                     shutdownHooks.remove(task);
                 }
             });
         }
     }
 
     private boolean runShutdownHooks() {
         boolean ran = false;
         // Note shutdown hooks can add / remove shutdown hooks.
         while (!shutdownHooks.isEmpty()) {
             List<Runnable> copy = new ArrayList<Runnable>(shutdownHooks);
             shutdownHooks.clear();
             for (Runnable task: copy) {
                 try {
                     task.run();
                 } catch (Throwable t) {
                     logger.warn("Shutdown hook raised an exception.", t);
                 } finally {
                     ran = true;
                 }
             }
         }
 
         if (ran) {
             lastExecutionTime = ScheduledFutureTask.nanoTime();
         }
 
         return ran;
     }
 
     @Override
     public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
         if (quietPeriod < 0) {
             throw new IllegalArgumentException("quietPeriod: " + quietPeriod + " (expected >= 0)");
         }
         if (timeout < quietPeriod) {
             throw new IllegalArgumentException(
                     "timeout: " + timeout + " (expected >= quietPeriod (" + quietPeriod + "))");
         }
         if (unit == null) {
             throw new NullPointerException("unit");
         }
 
         if (isShuttingDown()) {
             return terminationFuture();
         }
 
         boolean inEventLoop = inEventLoop();
         boolean wakeup;
         int oldState;
         for (;;) {
             if (isShuttingDown()) {
                 return terminationFuture();
             }
             int newState;
             wakeup = true;
             oldState = state;
             if (inEventLoop) {
                 newState = ST_SHUTTING_DOWN;
             } else {
                 switch (oldState) {
                     case ST_NOT_STARTED:
                     case ST_STARTED:
                         newState = ST_SHUTTING_DOWN;
                         break;
                     default:
                         newState = oldState;
                         wakeup = false;
                 }
             }
             if (STATE_UPDATER.compareAndSet(this, oldState, newState)) {
                 break;
             }
         }
         gracefulShutdownQuietPeriod = unit.toNanos(quietPeriod);
         gracefulShutdownTimeout = unit.toNanos(timeout);
 
         if (oldState == ST_NOT_STARTED) {
             thread.start();
         }
 
         if (wakeup) {
             wakeup(inEventLoop);
         }
 
         return terminationFuture();
     }
 
     @Override
     public Future<?> terminationFuture() {
         return terminationFuture;
     }
 
     @Override
     @Deprecated
     public void shutdown() {
         if (isShutdown()) {
             return;
         }
 
         boolean inEventLoop = inEventLoop();
         boolean wakeup;
         int oldState;
         for (;;) {
             if (isShuttingDown()) {
                 return;
             }
             int newState;
             wakeup = true;
             oldState = state;
             if (inEventLoop) {
                 newState = ST_SHUTDOWN;
             } else {
                 switch (oldState) {
                     case ST_NOT_STARTED:
                     case ST_STARTED:
                     case ST_SHUTTING_DOWN:
                         newState = ST_SHUTDOWN;
                         break;
                     default:
                         newState = oldState;
                         wakeup = false;
                 }
             }
             if (STATE_UPDATER.compareAndSet(this, oldState, newState)) {
                 break;
             }
         }
 
         if (oldState == ST_NOT_STARTED) {
             thread.start();
         }
 
         if (wakeup) {
             wakeup(inEventLoop);
         }
     }
 
     @Override
     public boolean isShuttingDown() {
         return state >= ST_SHUTTING_DOWN;
     }
 
     @Override
     public boolean isShutdown() {
         return state >= ST_SHUTDOWN;
     }
 
     @Override
     public boolean isTerminated() {
         return state == ST_TERMINATED;
     }
 
     /**
      * Confirm that the shutdown if the instance should be done now!
      */
     protected boolean confirmShutdown() {
         if (!isShuttingDown()) {
             return false;
         }
 
         if (!inEventLoop()) {
             throw new IllegalStateException("must be invoked from an event loop");
         }
 
         cancelScheduledTasks();
 
         if (gracefulShutdownStartTime == 0) {
             gracefulShutdownStartTime = ScheduledFutureTask.nanoTime();
         }
 
         if (runAllTasks() || runShutdownHooks()) {
             if (isShutdown()) {
                 // Executor shut down - no new tasks anymore.
                 return true;
             }
 
             // There were tasks in the queue. Wait a little bit more until no tasks are queued for the quiet period or
             // terminate if the quiet period is 0.
             // See https://github.com/netty/netty/issues/4241
             if (gracefulShutdownQuietPeriod == 0) {
                 return true;
             }
             wakeup(true);
             return false;
         }
 
         final long nanoTime = ScheduledFutureTask.nanoTime();
 
         if (isShutdown() || nanoTime - gracefulShutdownStartTime > gracefulShutdownTimeout) {
             return true;
         }
 
         if (nanoTime - lastExecutionTime <= gracefulShutdownQuietPeriod) {
             // Check if any tasks were added to the queue every 100ms.
             // TODO: Change the behavior of takeTask() so that it returns on timeout.
             wakeup(true);
             try {
                 Thread.sleep(100);
             } catch (InterruptedException e) {
                 // Ignore
             }
 
             return false;
         }
 
         // No tasks were added for last quiet period - hopefully safe to shut down.
         // (Hopefully because we really cannot make a guarantee that there will be no execute() calls by a user.)
         return true;
     }
 
     @Override
     public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
         if (unit == null) {
             throw new NullPointerException("unit");
         }
 
         if (inEventLoop()) {
             throw new IllegalStateException("cannot await termination of the current thread");
         }
 
         if (threadLock.tryAcquire(timeout, unit)) {
             threadLock.release();
         }
 
         return isTerminated();
     }
 
     @Override
     public void execute(Runnable task) {
         if (task == null) {
             throw new NullPointerException("task");
         }
 
         boolean inEventLoop = inEventLoop();
         if (inEventLoop) {
             addTask(task);
         } else {
             startThread();
             addTask(task);
             if (isShutdown() && removeTask(task)) {
                 reject();
             }
         }
 
         if (!addTaskWakesUp && wakesUpForTask(task)) {
             wakeup(inEventLoop);
         }
     }
 
     @Override
     public <T> T invokeAny(Collection<? extends Callable<T>> tasks) throws InterruptedException, ExecutionException {
         throwIfInEventLoop("invokeAny");
         return super.invokeAny(tasks);
     }
 
     @Override
     public <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
             throws InterruptedException, ExecutionException, TimeoutException {
         throwIfInEventLoop("invokeAny");
         return super.invokeAny(tasks, timeout, unit);
     }
 
     @Override
     public <T> List<java.util.concurrent.Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
             throws InterruptedException {
         throwIfInEventLoop("invokeAll");
         return super.invokeAll(tasks);
     }
 
     @Override
     public <T> List<java.util.concurrent.Future<T>> invokeAll(
             Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException {
         throwIfInEventLoop("invokeAll");
         return super.invokeAll(tasks, timeout, unit);
     }
 
     private void throwIfInEventLoop(String method) {
         if (inEventLoop()) {
             throw new RejectedExecutionException("Calling " + method + " from within the EventLoop is not allowed");
         }
     }
 
     /**
      * Returns the {@link ThreadProperties} of the {@link Thread} that powers the {@link SingleThreadEventExecutor}.
      */
     public final ThreadProperties threadProperties() {
         return threadProperties;
     }
 
     @SuppressWarnings("unused")
     protected boolean wakesUpForTask(Runnable task) {
         return true;
     }
 
     protected static void reject() {
         throw new RejectedExecutionException("event executor terminated");
     }
 
     // ScheduledExecutorService implementation
 
     private static final long SCHEDULE_PURGE_INTERVAL = TimeUnit.SECONDS.toNanos(1);
 
     private void startThread() {
         if (state == ST_NOT_STARTED) {
             if (STATE_UPDATER.compareAndSet(this, ST_NOT_STARTED, ST_STARTED)) {
                 thread.start();
             }
         }
     }
 
     private static final class DefaultThreadProperties implements ThreadProperties {
         private final Thread t;
 
         DefaultThreadProperties(Thread t) {
             this.t = t;
         }
 
         @Override
         public State state() {
             return t.getState();
         }
 
         @Override
         public int priority() {
             return t.getPriority();
         }
 
         @Override
         public boolean isInterrupted() {
             return t.isInterrupted();
         }
 
         @Override
         public boolean isDaemon() {
             return t.isDaemon();
         }
 
         @Override
         public String name() {
             return t.getName();
         }
 
         @Override
         public long id() {
             return t.getId();
         }
 
         @Override
         public StackTraceElement[] stackTrace() {
             return t.getStackTrace();
         }
 
         @Override
         public boolean isAlive() {
             return t.isAlive();
         }
     }
 }