Class QueuedExecutor
- java.lang.Object
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- EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser
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- EDU.oswego.cs.dl.util.concurrent.QueuedExecutor
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- 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 ifrestart()
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.
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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.-
Nested classes/interfaces inherited from class EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser
ThreadFactoryUser.DefaultThreadFactory
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Field Summary
Fields Modifier and Type Field Description protected static java.lang.Runnable
ENDTASK
Special queue element to signal terminationprotected Channel
queue_
The queueprotected QueuedExecutor.RunLoop
runLoop_
protected boolean
shutdown_
true if thread should shut down after processing current taskprotected java.lang.Thread
thread_
The thread used to process commands-
Fields inherited from class EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser
threadFactory_
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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.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description protected void
clearThread()
set thread_ to null to indicate terminationvoid
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 EDU.oswego.cs.dl.util.concurrent.ThreadFactoryUser
getThreadFactory, setThreadFactory
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Field Detail
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thread_
protected java.lang.Thread thread_
The thread used to process commands
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ENDTASK
protected static java.lang.Runnable ENDTASK
Special queue element to signal termination
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shutdown_
protected volatile boolean shutdown_
true if thread should shut down after processing current task
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queue_
protected final Channel queue_
The queue
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runLoop_
protected final QueuedExecutor.RunLoop runLoop_
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Constructor Detail
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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.
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QueuedExecutor
public QueuedExecutor()
Construct a new QueuedExecutor that uses a BoundedLinkedQueue with the current DefaultChannelCapacity as its queue.
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Method Detail
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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.
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clearThread
protected void clearThread()
set thread_ to null to indicate termination
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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.
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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.
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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.
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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.
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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.
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