Class QueuedExecutor

java.lang.Object
EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser
EDU.oswego.cs.dl.util.concurrent.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. ]

  • Field Details

    • thread_

      protected Thread thread_
      The thread used to process commands
    • ENDTASK

      protected static 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
    • runLoop_

      protected final QueuedExecutor.RunLoop runLoop_
  • Constructor Details

    • 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 Details

    • getThread

      public 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(Runnable command) throws 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:
      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.