package com.atlassian.plugin.osgi.spring;
   
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   import org.springframework.core.task.AsyncTaskExecutor;
   
   import javax.annotation.Nonnull;
   import java.util.concurrent.Callable;
   import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Future;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * Executes spring tasks using a cached thread pool that expands as necessary. Overrides the default Spring executor
   * that spawns a new thread for every application context creation.
   *
   * @since 2.5.0
   */
  public class ThreadPoolAsyncTaskExecutor implements AsyncTaskExecutor {
      private static final Logger log = LoggerFactory.getLogger(ThreadPoolAsyncTaskExecutor.class);
  
      private final ExecutorService executor = Executors.newCachedThreadPool(new NamedThreadFactory());
  
      /**
       * Executes the runnable
       *
       * @param task         The runnable task
       * @param startTimeout The start timeout (ignored)
       */
      @Override
      public void execute(@Nonnull Runnable task, long startTimeout) {
          // yes, we ignore the start timeout
          executor.execute(task);
      }
  
      @Nonnull
      @Override
      public Future<?> submit(@Nonnull Runnable task) {
          return executor.submit(task);
      }
  
      @Nonnull
      @Override
      public <T> Future<T> submit(@Nonnull Callable<T> task) {
          return executor.submit(task);
      }
  
      /**
       * Executes the runnable
       *
       * @param task The runnable task
       */
      @Override
      public void execute(@Nonnull Runnable task) {
          this.execute(task, -1);
      }
  
      /**
       * Shuts down the internal {@code ExecutorService} to ensure that all threads are stopped in order to allow the JVM
       * to terminate cleanly in a timely fashion.
       */
      public void shutdown() {
          log.debug("Attempting to shutdown ExecutorService");
  
          executor.shutdown();
          try {
              if (executor.awaitTermination(5, TimeUnit.SECONDS)) {
                  log.debug("ExecutorService has shutdown gracefully");
              } else {
                  //The executor did not shutdown within the timeout. We can't wait forever, though, so issue a
                  //shutdownNow() and give it another 5 seconds
                  log.warn("ExecutorService did not shutdown within the timeout; forcing shutdown");
  
                  executor.shutdownNow();
                  if (executor.awaitTermination(5, TimeUnit.SECONDS)) {
                      //The forced shutdown has brought the executor down. Not ideal, but acceptable
                      log.debug("ExecutorService has been forced to shutdown");
                  } else {
                      //We can't delay execution indefinitely waiting, so log a warning. The JVM may not shut down
                      //if this service does not stop (because it uses non-daemon threads), so this may be helpful
                      //in debugging should that happen.
                      log.warn("ExecutorService did not shutdown; it will be abandoned");
                  }
              }
          } catch (InterruptedException e) {
              log.warn("Interrupted while waiting for the executor service to shutdown; some worker threads may " +
                      "still be running");
              Thread.currentThread().interrupt();
          }
      }
  
      /**
       * Thread factory that names the threads for the executor
       */
      private static class NamedThreadFactory implements ThreadFactory {
          private final AtomicInteger counter = new AtomicInteger();
 
         @Override
         public Thread newThread(@Nonnull Runnable r) {
             Thread thread = new Thread(r);
             thread.setDaemon(false);
             thread.setName("ThreadPoolAsyncTaskExecutor::Thread " + counter.incrementAndGet());
             return thread;
         }
     }
 }