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 org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.concurrent.TimeUnit;
  
  import com.google.common.annotations.VisibleForTesting;
  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
  import java.util.function.BiFunction;
  import java.util.function.Consumer;
  
  import org.apache.cassandra.concurrent.ExecutorFactory.SimulatorThreadTag;
  import org.apache.cassandra.concurrent.ExecutorFactory.SystemThreadTag;
  import org.apache.cassandra.utils.Shared;
  import org.apache.cassandra.utils.concurrent.Condition;
  import org.apache.cassandra.utils.concurrent.UncheckedInterruptedException;
  
  import static org.apache.cassandra.concurrent.InfiniteLoopExecutor.InternalState.SHUTTING_DOWN_NOW;
  import static org.apache.cassandra.concurrent.InfiniteLoopExecutor.InternalState.TERMINATED;
  import static org.apache.cassandra.concurrent.InfiniteLoopExecutor.Interrupts.SYNCHRONIZED;
  import static org.apache.cassandra.concurrent.InfiniteLoopExecutor.Interrupts.UNSYNCHRONIZED;
  import static org.apache.cassandra.concurrent.Interruptible.State.INTERRUPTED;
  import static org.apache.cassandra.concurrent.Interruptible.State.NORMAL;
  import static org.apache.cassandra.concurrent.Interruptible.State.SHUTTING_DOWN;
  import static org.apache.cassandra.utils.Clock.Global.nanoTime;
  import static org.apache.cassandra.utils.concurrent.Condition.newOneTimeCondition;
  
  public class InfiniteLoopExecutor implements Interruptible
  {
      private static final Logger logger = LoggerFactory.getLogger(InfiniteLoopExecutor.class);
  
      @Shared(scope = Shared.Scope.SIMULATION)
      public enum InternalState { SHUTTING_DOWN_NOW, TERMINATED }
  
      @Shared(scope = Shared.Scope.SIMULATION)
      public enum SimulatorSafe { SAFE, UNSAFE }
  
      @Shared(scope = Shared.Scope.SIMULATION)
      public enum Interrupts    { SYNCHRONIZED, UNSYNCHRONIZED }
  
      private static final AtomicReferenceFieldUpdater<InfiniteLoopExecutor, Object> stateUpdater = AtomicReferenceFieldUpdater.newUpdater(InfiniteLoopExecutor.class, Object.class, "state");
      private final Thread thread;
      private final Task task;
      private volatile Object state = NORMAL;
      private final Consumer<Thread> interruptHandler;
      private final Condition isTerminated = newOneTimeCondition();
  
      public InfiniteLoopExecutor(String name, Task task, SystemThreadTag systemTag)
      {
          this(ExecutorFactory.Global.executorFactory(), name, task, systemTag, UNSYNCHRONIZED);
      }
  
      public InfiniteLoopExecutor(ExecutorFactory factory, String name, Task task, SystemThreadTag systemTag)
      {
          this(factory, name, task, systemTag, UNSYNCHRONIZED);
      }
  
      public InfiniteLoopExecutor(ExecutorFactory factory, String name, Task task, SystemThreadTag systemTag, Interrupts interrupts)
      {
          this.task = task;
          this.thread = factory.startThread(name, this::loop, systemTag, SimulatorThreadTag.INFINITE_LOOP);
          this.interruptHandler = interrupts == SYNCHRONIZED
                                  ? interruptHandler(task)
                                  : Thread::interrupt;
      }
  
      public InfiniteLoopExecutor(BiFunction<String, Runnable, Thread> threadStarter, String name, Task task, Interrupts interrupts)
      {
          this.task = task;
          this.thread = threadStarter.apply(name, this::loop);
          this.interruptHandler = interrupts == SYNCHRONIZED
                                  ? interruptHandler(task)
                                  : Thread::interrupt;
      }
  
      private static Consumer<Thread> interruptHandler(final Object monitor)
      {
          return thread -> {
              synchronized (monitor)
              {
                  thread.interrupt();
              }
          };
      }
  
      private void loop()
      {
          boolean interrupted = false;
          try
          {
              while (true)
              {
                  try
                  {
                      Object cur = state;
                      if (cur == SHUTTING_DOWN_NOW) break;
  
                      interrupted |= Thread.interrupted();
                      if (cur == NORMAL && interrupted) cur = INTERRUPTED;
                      task.run((State) cur);
  
                      interrupted = false;
                      if (cur == SHUTTING_DOWN) break;
                  }
                  catch (TerminateException ignore)
                  {
                      break;
                  }
                  catch (UncheckedInterruptedException | InterruptedException ignore)
                  {
                      interrupted = true;
                  }
                  catch (Throwable t)
                  {
                      logger.error("Exception thrown by runnable, continuing with loop", t);
                  }
              }
          }
          finally
          {
              state = TERMINATED;
              isTerminated.signal();
          }
      }
  
      public void interrupt()
      {
          interruptHandler.accept(thread);
      }
  
      public void shutdownGracefully()
      {
          stateUpdater.updateAndGet(this, cur -> cur != TERMINATED && cur != SHUTTING_DOWN_NOW ? SHUTTING_DOWN : cur);
      }
  
      public void shutdown()
      {
          shutdown(true);
      }
  
      public void shutdown(boolean interrupt)
      {
          stateUpdater.updateAndGet(this, cur -> cur != TERMINATED && cur != SHUTTING_DOWN_NOW ? SHUTTING_DOWN : cur);
          if (interrupt)
              interruptHandler.accept(thread);
      }
  
      public Object shutdownNow()
      {
          stateUpdater.updateAndGet(this, cur -> cur != TERMINATED ? SHUTTING_DOWN_NOW : TERMINATED);
          interruptHandler.accept(thread);
          return null;
      }
  
      @Override
      public boolean isTerminated()
      {
          return state == TERMINATED;
      }
  
      public boolean awaitTermination(long time, TimeUnit unit) throws InterruptedException
      {
          if (isTerminated())
              return true;
  
          long deadlineNanos = nanoTime() + unit.toNanos(time);
          isTerminated.awaitUntil(deadlineNanos);
          return isTerminated();
      }
  
      public long threadId()
      {
          return thread.getId();
      }
  
      @VisibleForTesting
      public boolean isAlive()
      {
          return this.thread.isAlive();
      }
  }
  