Home » concurrent-sources » EDU.oswego.cs.dl.util.concurrent » [javadoc | source]

EDU.oswego.cs.dl.util.concurrent
public class: QueuedExecutor [javadoc | source]

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

All Implemented Interfaces:
    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:
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.

Field Summary
protected  Thread	thread_	The thread used to process commands
protected static  Runnable	ENDTASK	Special queue element to signal termination
protected volatile  boolean	shutdown_	true if thread should shut down after processing current task
protected final  Channel	queue_	The queue *
protected final  RunLoop	runLoop_

Fields inherited from EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser:
threadFactory_

Constructor:
public QueuedExecutor() { this(new BoundedLinkedQueue()); } Construct a new QueuedExecutor that uses a BoundedLinkedQueue with the current DefaultChannelCapacity as its queue.
public QueuedExecutor(Channel queue) { queue_ = queue; runLoop_ = new RunLoop(); } 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.

Method from EDU.oswego.cs.dl.util.concurrent.QueuedExecutor Summary:
clearThread,   execute,   getThread,   restart,   shutdownAfterProcessingCurrentTask,   shutdownAfterProcessingCurrentlyQueuedTasks,   shutdownNow

Methods from EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser:
getThreadFactory,   setThreadFactory

Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait

Method from EDU.oswego.cs.dl.util.concurrent.QueuedExecutor Detail:
protected synchronized void clearThread() { thread_ = null; } set thread_ to null to indicate termination *
public void execute(Runnable command) throws InterruptedException { restart(); queue_.put(command); } 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.
public synchronized Thread getThread() { return thread_; } 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.
public synchronized void restart() { if (thread_ == null && !shutdown_) { thread_ = threadFactory_.newThread(runLoop_); thread_.start(); } } 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.
public synchronized void shutdownAfterProcessingCurrentTask() { shutdown_ = true; try { while (queue_.poll(0) != null) ; // drain queue_.put(ENDTASK); } catch (InterruptedException ex) { Thread.currentThread().interrupt(); } } Terminate background thread after it processes the current task, removing other queued tasks and leaving them unprocessed. A shut down thread cannot be restarted. *
public synchronized void shutdownAfterProcessingCurrentlyQueuedTasks() { if (!shutdown_) { try { queue_.put(ENDTASK); } catch (InterruptedException ex) { Thread.currentThread().interrupt(); } } } 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.
public synchronized void shutdownNow() { shutdown_ = true; Thread t = thread_; if (t != null) t.interrupt(); shutdownAfterProcessingCurrentTask(); } 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.