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study:java:threadpool [2011/08/03 04:08] – [Are We Done Yet?] bananastudy:java:threadpool [2011/08/03 04:11] (現在) – [TestThreadPool.java] banana
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 ====== Are We Done Yet? ====== ====== Are We Done Yet? ======
-thread pool이 task를 완료했는지 알려면 몇가지를 체크해야 한다. 첫째는 assignment array가 비어있어야 한다. //+thread pool이 task를 완료했는지 알려면 몇가지를 체크해야 한다. 첫째는 assignment array가 비어있어야 한다. \\
 하지만 이것은 필요조건이지 충분조건은 아니다. 비어있다고 해도 pool안에는 실행되고 있는 %%WorkerThread%%가 존재할수도 있다.\\ 하지만 이것은 필요조건이지 충분조건은 아니다. 비어있다고 해도 pool안에는 실행되고 있는 %%WorkerThread%%가 존재할수도 있다.\\
 thread pool이 작업완료 되었는지 검사하는 class가 %%Done.java%% 클래스이다. 하지만 사용할 때에는 직접 접근하지 않아도 된다.\\ 단지 task를 assign으로 할당하고 complete메소드를 부르기만 하면 된다. %%Done%% class는 두 메소드를 가지고 있다.\\ thread pool이 작업완료 되었는지 검사하는 class가 %%Done.java%% 클래스이다. 하지만 사용할 때에는 직접 접근하지 않아도 된다.\\ 단지 task를 assign으로 할당하고 complete메소드를 부르기만 하면 된다. %%Done%% class는 두 메소드를 가지고 있다.\\
 %%WorkerThread%%가 시작될때 불리는 workerBegin메소드와 종료될 때 불리는 workerEnd메소드가 그것이다.\\ %%WorkerThread%%가 시작될때 불리는 workerBegin메소드와 종료될 때 불리는 workerEnd메소드가 그것이다.\\
 다음으로 thread pool example을 살펴본다. 다음으로 thread pool example을 살펴본다.
 +
 +===== ThreadPool.java =====
 +<code java>
 +package thread;
 +
 +import java.util.ArrayList;
 +import java.util.Collection;
 +
 +/**
 + * Java Thread Pool
 + * 
 + * This is a thread pool that for Java, it is
 + * simple to use and gets the job done. This program and
 + * all supporting files are distributed under the Limited
 + * GNU Public License (LGPL, http://www.gnu.org).
 + * 
 + * This is the main class for the thread pool. You should
 + * create an instance of this class and assign tasks to it.
 + * 
 + * For more information visit http://www.jeffheaton.com.
 + * 
 + * @author Jeff Heaton (http://www.jeffheaton.com)
 + * @version 1.0
 + */
 +public class ThreadPool {
 + /**
 +   * The threads in the pool.
 +   */
 + protected Thread threads[] = null;
 + /**
 +   * The backlog of assignments, which are waiting
 +   * for the thread pool.
 +   */
 + Collection assignments = new ArrayList(3);
 + /**
 +   * A Done object that is used to track when the
 +   * thread pool is done, that is has no more work
 +   * to perform.
 +   */
 + protected Done done = new Done();
 +
 + /**
 +   * The constructor.
 +   * 
 +   * @param size  How many threads in the thread pool.
 +   */
 + public ThreadPool(int size)
 + {
 +   threads = new WorkerThread[size];
 +   for (int i=0;i<threads.length;i++) {
 +    threads[i] = new WorkerThread(this);
 +    threads[i].start();
 +   }
 + }
 +
 + /**
 +   * Add a task to the thread pool. Any class
 +   * which implements the Runnable interface
 +   * may be assienged. When this task runs, its
 +   * run method will be called.
 +   * 
 +   * @param r   An object that implements the Runnable interface
 +   */
 + public synchronized void assign(Runnable r)
 + {
 +   done.workerBegin();
 +   assignments.add(r);
 +   notify();
 + }
 +
 + /**
 +   * Get a new work assignment.
 +   * 
 +   * @return A new assignment
 +   */
 + public synchronized Runnable getAssignment()
 + {
 +   try {
 +    while ( !assignments.iterator().hasNext() )
 +    wait();
 +
 +    Runnable r = (Runnable)assignments.iterator().next();
 +    assignments.remove(r);
 +    return r;
 +   } catch (InterruptedException e) {
 +    done.workerEnd();
 +    return null;
 +   }
 + }
 +
 + /**
 +   * Called to block the current thread until
 +   * the thread pool has no more work.
 +   */
 + public void complete()
 + {
 +   done.waitBegin();
 +   done.waitDone();
 + }
 +
 +
 + protected void finalize()  
 + {
 +   done.reset();
 +   for (int i=0;i<threads.length;i++) {
 +    threads[i].interrupt();
 +    done.workerBegin();
 +    threads[i].destroy();
 +   }
 +   done.waitDone();
 + }
 +}
 +</code>
 +
 +===== WorkerThread.java =====
 +<code java>
 +package thread;
 +
 +/**
 + * The worker threads that make up the thread pool.
 + * 
 + * @author Jeff Heaton
 + * @version 1.0
 + */
 +class WorkerThread extends Thread {
 + /**
 +   * True if this thread is currently processing.
 +   */
 + public boolean busy;
 + /**
 +   * The thread pool that this object belongs to.
 +   */
 + public ThreadPool owner;
 +
 + /**
 +   * The constructor.
 +   * 
 +   * @param o the thread pool 
 +   */
 + WorkerThread(ThreadPool o)
 + {
 + owner = o;
 + }
 +
 + /**
 +   * Scan for and execute tasks.
 +   */
 + public void run()
 + {
 +   Runnable target = null;
 +
 +   do {
 +    target = owner.getAssignment();
 +    if (target!=null) {
 +     target.run();      
 +     owner.done.workerEnd();
 +    }
 +   } while (target!=null);
 + }
 +}
 +
 +</code>
 +
 +===== Done.java =====
 +<code java>
 +package thread;
 +
 +/**
 + * 
 + * This is a thread pool for Java, it is
 + * simple to use and gets the job done. This program and
 + * all supporting files are distributed under the Limited
 + * GNU Public License (LGPL, http://www.gnu.org).
 + * 
 + * This is a very simple object that
 + * allows the TheadPool to determine when 
 + * it is done. This object implements
 + * a simple lock that the ThreadPool class
 + * can wait on to determine completion.
 + * Done is defined as the ThreadPool having
 + * no more work to complete.
 + * 
 + * Copyright 2001 by Jeff Heaton
 + *
 + * @author Jeff Heaton (http://www.jeffheaton.com)
 + * @version 1.0
 + */
 +public class Done {
 +
 + /**
 +   * The number of Worker object
 +   * threads that are currently working
 +   * on something.
 +   */
 + private int _activeThreads = 0;
 +
 + /**
 +   * This boolean keeps track of if
 +   * the very first thread has started
 +   * or not. This prevents this object
 +   * from falsely reporting that the ThreadPool 
 +   * is done, just because the first thread
 +   * has not yet started.
 +   */
 + private boolean _started = false;
 +
 + /**
 +   * This method can be called to block
 +   * the current thread until the ThreadPool
 +   * is done.
 +   */
 + synchronized public void waitDone()
 + {
 +   try {
 +    while ( _activeThreads>0 ) {
 +    wait();
 +    }
 +   } catch ( InterruptedException e ) {
 +   }
 + }
 + /**
 +   * Called to wait for the first thread to 
 +   * start. Once this method returns the
 +   * process has begun.
 +   */
 +
 + synchronized public void waitBegin()
 + {
 +   try {
 +    while ( !_started ) {
 +    wait();
 +    }
 +   } catch ( InterruptedException e ) {
 +   }
 + }
 +
 +
 + /**
 +   * Called by a Worker object
 +   * to indicate that it has begun 
 +   * working on a workload.
 +   */
 + synchronized public void workerBegin()
 + {
 +   _activeThreads++;
 +   _started = true;
 +   notify();
 + }
 +
 + /**
 +   * Called by a Worker object to 
 +   * indicate that it has completed a 
 +   * workload.
 +   */
 + synchronized public void workerEnd()
 + {
 +   _activeThreads--;
 +   notify();
 + }
 +
 + /**
 +   * Called to reset this object to
 +   * its initial state.
 +   */
 + synchronized public void reset()
 + {
 + _activeThreads = 0;
 + }
 +
 +}
 +
 +</code>
 +
 +===== TestWorkerThread.java =====
 +<code java>
 +package thread;
 +
 +/**
 + * This class shows an example worker thread that can
 + * be used with the thread pool. It demonstrates the main
 + * points that should be included in any worker thread. Use
 + * this as a starting point for your own threads.
 + * 
 + * @author Jeff Heaton (http://www.jeffheaton.com)
 + * @version 1.0
 + */
 +public class TestWorkerThread implements Runnable {
 + static private int count = 0;
 + private int taskNumber;
 + protected Done done;
 +
 + /**
 +   * 
 +   * @param done
 +   */
 + TestWorkerThread()
 + {
 +   count++;
 +   taskNumber = count;
 + }
 +
 + public void run()
 + {
 +   for (int i=0;i<100;i+=2) {
 +    System.out.println("Task number: " + taskNumber + ",percent complete = " + i );
 +    try {
 +    Thread.sleep((int)(Math.random()*500));
 +    } catch (InterruptedException e) {
 +    }
 +   }
 + }
 +}
 +
 +</code>
 +
 +===== TestThreadPool.java =====
 +<code java>
 +package thread;
 +
 +/**
 + * thread pool
 + * 
 + * @author Jeff Heaton (http://www.jeffheaton.com)
 + * @version 1.0
 + */
 +public class TestThreadPool {
 + /**
 +   * 
 +   * 
 +   * @param args  No arguments are used.
 +   */
 + public static void main(String args[])
 + {
 +   ThreadPool pool = new ThreadPool(10);
 +
 +   for (int i=1;i<25;i++) {
 +   pool.assign(new TestWorkerThread());
 +   }
 +
 +   pool.complete();
 +
 +   System.out.println("All tasks are done.");
 + }
 +}
 +
 +</code>
 +
 +====== reference ======
 +  - [[http://www.informit.com/articles/article.aspx?p=30483&seqNum=1| Creating a Thread Pool with Java]]
 +

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