花了很多的时间和线程池的概念之后，并通过博客上的数字阅读不同的代码和Stackoverflow.com张贴问题，现在我得到这个概念的清晰图像。 但是在此期间，我发现代码中的一些疑惑。
当pool.assign（新TestWorkerThread（））; 在TestThreadPool类执行时，它调用done.workerBegin（）; 方法，该方法是在完成类 ，在那里它递增_activeThreads变量。 但我认为是， 逻辑上是不正确的，因为如果线程数较少（在这种情况下，2）比的任务（在TestThreadPool类给出）的数量（在这种情况下5），它增加_activeThreads（即_activeThreads = 5 ）计数不必要的。
什么_started变量确实在做类 ？
waitDone（）和waitBegin（）（在做类 ）如何执行其运作？ （如果你能解释一下这两种方法一步一步这是件好事。）
代码如下。 我根据其流量分配的代码。
TestThreadPool类： -
package hitesh;
/**
*
* @author jhamb
*/
public class TestThreadPool {
public static void main(String args[]) throws InterruptedException
{
ThreadPool pool = new ThreadPool(2);
for (int i = 1;i <= 5;i++) {
pool.assign(new TestWorkerThread());
}
System.out.println("All tasks are assigned");
pool.complete();
System.out.println("All tasks are done.");
}
}
TestWorkerThread类： -
package hitesh;
/**
*
* @author jhamb
*/
/**
* 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.
*/
public class TestWorkerThread implements Runnable {
static private int count = 0;
private int taskNumber;
protected Done done;
/**
*
* @param done
*/
TestWorkerThread()
{
count++;
taskNumber = count;
//System.out.println("tasknumber ---> " + taskNumber);
}
public void run()
{
System.out.println("TWT run starts --> " + this.toString());
for (int i=0;i <= 100;i += 25) {
System.out.println("Task number: " + taskNumber +
",percent complete = " + i );
try {
Thread.sleep((int)(Math.random()*500));
} catch (InterruptedException e) {
}
}
System.out.println("task for thread --> " + this.toString() + " completed");
}
}
ThreadPool类： -
package hitesh;
/**
*
* @author jhamb
*/
import java.util.*;
/*
* This is the main class for the thread pool. You should
* create an instance of this class and assign tasks to it.
*/
public class ThreadPool {
protected Thread threads[] = null;
Collection assignments = new ArrayList(3);
protected Done done = new Done();
public ThreadPool(int size) throws InterruptedException
{
threads = new WorkerThread[size];
for (int i=0;i<threads.length;i++) {
threads[i] = new WorkerThread(this);
threads[i].start();
System.out.println ("thread " + i + " started");
threads[i].sleep(1000);
}
}
public synchronized void assign(Runnable r)
{
done.workerBegin();
assignments.add(r);
System.out.println("Collection size ---> " + assignments.size() + " Thread can work on this");
notify();
}
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;
}
}
public void complete()
{
done.waitBegin();
done.waitDone();
}
}
的WorkerThread类： -
package hitesh;
import java.util.*;
/**
*
* @author jhamb
*/
/**
* The worker threads that make up the thread pool.
*/
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.
*/
//@Override
public void run()
{
System.out.println("Threads name : "+ this.getName() + " working.....");
Runnable target = null;
do {
System.out.println("enter in do while " + this.getName() );
target = owner.getAssignment();
System.out.println("GetAssignment k aage aa gya mai " + target);
if (target!=null) {
target.run();
//target.
owner.done.workerEnd();
}
} while (target!=null);
System.out.println("do while finishes for "+ this.getName());
}
}
完成等级： -
package hitesh;
/**
*
* @author jhamb
*/
/**
*
* 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;
}
}
请帮忙。 提前致谢。 寻找你的一种回应。
