Class QueuedExecutor

  • All Implemented Interfaces:
    Executor

    public class QueuedExecutor
    extends ThreadFactoryUser
    implements Executor
    An implementation of Executor that queues incoming requests until they can be processed by a single background thread.

    The thread is not actually started until the first execute request is encountered. Also, if the thread is stopped for any reason (for example, after hitting an unrecoverable exception in an executing task), one is started upon encountering a new request, or if restart() is invoked.

    Beware that, especially in situations where command objects themselves invoke execute, queuing can sometimes lead to lockups, since commands that might allow other threads to terminate do not run at all when they are in the queue.

    [ Introduction to this package. ]

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      protected class  QueuedExecutor.RunLoop
      The runloop is isolated in its own Runnable class just so that the main class need not implement Runnable, which would allow others to directly invoke run, which would never make sense here.
    • Constructor Summary

      Constructors 
      Constructor Description
      QueuedExecutor()
      Construct a new QueuedExecutor that uses a BoundedLinkedQueue with the current DefaultChannelCapacity as its queue.
      QueuedExecutor​(Channel queue)
      Construct a new QueuedExecutor that uses the supplied Channel as its queue.
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      protected void clearThread()
      set thread_ to null to indicate termination
      void execute​(java.lang.Runnable command)
      Arrange for execution of the command in the background thread by adding it to the queue.
      java.lang.Thread getThread()
      Return the thread being used to process commands, or null if there is no such thread.
      void restart()
      Start (or restart) the background thread to process commands.
      void shutdownAfterProcessingCurrentlyQueuedTasks()
      Terminate background thread after it processes all elements currently in queue.
      void shutdownAfterProcessingCurrentTask()
      Terminate background thread after it processes the current task, removing other queued tasks and leaving them unprocessed.
      void shutdownNow()
      Terminate background thread even if it is currently processing a task.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • thread_

        protected java.lang.Thread thread_
        The thread used to process commands
      • ENDTASK

        protected static java.lang.Runnable ENDTASK
        Special queue element to signal termination
      • shutdown_

        protected volatile boolean shutdown_
        true if thread should shut down after processing current task
      • queue_

        protected final Channel queue_
        The queue
    • Constructor Detail

      • QueuedExecutor

        public QueuedExecutor​(Channel queue)
        Construct a new QueuedExecutor that uses the supplied Channel as its queue.

        This class does not support any methods that reveal this queue. If you need to access it independently (for example to invoke any special status monitoring operations), you should record a reference to it separately.

      • QueuedExecutor

        public QueuedExecutor()
        Construct a new QueuedExecutor that uses a BoundedLinkedQueue with the current DefaultChannelCapacity as its queue.
    • Method Detail

      • getThread

        public java.lang.Thread getThread()
        Return the thread being used to process commands, or null if there is no such thread. You can use this to invoke any special methods on the thread, for example, to interrupt it.
      • clearThread

        protected void clearThread()
        set thread_ to null to indicate termination
      • restart

        public void restart()
        Start (or restart) the background thread to process commands. It has no effect if a thread is already running. This method can be invoked if the background thread crashed due to an unrecoverable exception.
      • execute

        public void execute​(java.lang.Runnable command)
                     throws java.lang.InterruptedException
        Arrange for execution of the command in the background thread by adding it to the queue. The method may block if the channel's put operation blocks.

        If the background thread does not exist, it is created and started.

        Specified by:
        execute in interface Executor
        Throws:
        java.lang.InterruptedException
      • shutdownAfterProcessingCurrentlyQueuedTasks

        public void shutdownAfterProcessingCurrentlyQueuedTasks()
        Terminate background thread after it processes all elements currently in queue. Any tasks entered after this point will not be processed. A shut down thread cannot be restarted. This method may block if the task queue is finite and full. Also, this method does not in general apply (and may lead to comparator-based exceptions) if the task queue is a priority queue.
      • shutdownAfterProcessingCurrentTask

        public void shutdownAfterProcessingCurrentTask()
        Terminate background thread after it processes the current task, removing other queued tasks and leaving them unprocessed. A shut down thread cannot be restarted.
      • shutdownNow

        public void shutdownNow()
        Terminate background thread even if it is currently processing a task. This method uses Thread.interrupt, so relies on tasks themselves responding appropriately to interruption. If the current tasks does not terminate on interruption, then the thread will not terminate until processing current task. A shut down thread cannot be restarted.