我编写了一个简单的Java程序来帮助使用线程和线程池来完成某些任务。在我的程序中，有类TheObject的对象必须对它们进行某种处理（在这种情况下，只是睡眠延迟并打印出它们的字段）。
TheObject个对象放在一个队列中，WorkerThread从中抽取它们并处理它们。
我创建了一个Manager类，用于初始化TheObjects和WorkerThread。我运行它时会得到奇怪的输出;一个线程正在处理所有事情，而不是线程关闭工作！为什么会这样？如何让线程共享工作负载？
这是输出：
--------------------------------------------
alfred a 0
Thread-0
--------------------------------------------
bob b 1
Thread-0
--------------------------------------------
carl c 2
Thread-0
--------------------------------------------
dave d 3
Thread-0
--------------------------------------------
earl e 4
Thread-0
--------------------------------------------
fred f 5
Thread-0
--------------------------------------------
greg g 6
Thread-0
--------------------------------------------
harry h 7
Thread-0
--------------------------------------------
izzie i 8
Thread-0
--------------------------------------------
jim j 9
Thread-0
--------------------------------------------
kyle k 0
Thread-0
--------------------------------------------
Larry L 1
Thread-1
--------------------------------------------
Michael M 2
Thread-1
--------------------------------------------
Ned N 3
Thread-0
--------------------------------------------
Olaf O 4
Thread-0
--------------------------------------------
Peter P 5
Thread-0
--------------------------------------------
Quincy Q 6
Thread-0
--------------------------------------------
Raphael R 7
Thread-0
--------------------------------------------
Sam S 8
Thread-0
--------------------------------------------
Trixie T 9
Thread-0
守则：
类：
管理器
public class Manager {
public static void main(String[] args) throws InterruptedException {
TheObjectQueue queue = new TheObjectQueue();
//Create Objects
int numberOfInitialObjects = 10;
String[] arrayOfNames = {"alfred", "bob", "carl", "dave", "earl", "fred", "greg", "harry", "izzie", "jim"};
//char[] arrayOfChars = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'};
//int[] arrayOfNums = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
for (int i = 0; i < numberOfInitialObjects; i++){
TheObject anObject = new TheObject(arrayOfNames[i], arrayOfNames[i].charAt(0), i);
queue.addToQueue(anObject);
}
int numberOfThreads = 2;
for (int i = 0; i < numberOfThreads; i++){
WorkerThread workerThread = new WorkerThread(queue);
workerThread.start();
}
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String[] arrayOfNames2 = {"kyle", "Larry", "Michael", "Ned", "Olaf", "Peter", "Quincy", "Raphael", "Sam", "Trixie"};
for (int i = 0; i < numberOfInitialObjects; i++){
TheObject anObject = new TheObject(arrayOfNames2[i], arrayOfNames2[i].charAt(0), i);
queue.addToQueue(anObject);
}
}
}
TheObject
public class TheObject {
private String someName;
private char someChar;
private int someNum;
public TheObject(String someName, char someChar, int someNum) {
super();
this.someName = someName;
this.someChar = someChar;
this.someNum = someNum;
}
public String getSomeName() {
return someName;
}
public char getSomeChar() {
return someChar;
}
public int getSomeNum() {
return someNum;
}
}
TheObjectQueue
import java.util.LinkedList;
public class TheObjectQueue {
private LinkedList<TheObject> objectQueue = null;
public TheObjectQueue(){
objectQueue = new LinkedList<TheObject>();
}
public LinkedList<TheObject> getQueue(){
return objectQueue;
}
public void addToQueue(TheObject obj){
synchronized (this) {
objectQueue.addFirst(obj);
this.notify();
}
}
public TheObject removeFromQueue(){
synchronized (this) {
TheObject obj = objectQueue.removeLast();
return obj;
}
}
public int getSize(){
return objectQueue.size();
}
public boolean isEmpty(){
return objectQueue.isEmpty();
}
}
的WorkerThread
import java.util.Random;
public class WorkerThread extends Thread{
private TheObjectQueue queue;
public WorkerThread(TheObjectQueue queue){
this.queue = queue;
}
public void process(TheObject obj){
//Stall for a random amount of time
Random random = new Random();
int randomInt = random.nextInt(3)*1000;
try {
Thread.sleep(randomInt);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//Begin Printing
System.out.println("--------------------------------------------");
System.out.print(obj.getSomeName());
System.out.print(" ");
System.out.print(obj.getSomeChar());
System.out.print(" ");
System.out.println(obj.getSomeNum());
System.out.println(this.getName());
}
@Override
public void run() {
while(true){
synchronized (queue) {
while(queue.isEmpty()){
try {
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
TheObject objToDealWith = queue.removeFromQueue();
process(objToDealWith);
super.run();
}
}
}
}
答案 0 :(得分：2)
WorkerThread.run中的（共享）队列上的同步只允许单个线程一次处理一个任务 - 效果实际上是一个工作者池！在这种情况下，线程0＆＃34;赢得＆＃34;大多数时候获得锁定;同步锁定获取是not guaranteed to be fair。
一个简单的修复方法是使用所需的线程安全构造从队列中获取任务，然后处理同步部分的外部任务。这允许工人同时处理被认为是独立的任务。
// e.g.
@Override
public void run() {
while(true){
TheObject objToDealWith;
synchronized (queue) {
// Only synchronized on queue when fetching task
objToDealWith = getTask(queue);
}
// Process task; independent of queue
process(objToDealWith);
}
}
由于其中一个线程将忙于处理任务，而另一个线程正在获取（或已获得）队列锁定，因此工作分配将是公平的。＃/ p>
答案 1 :(得分：-1)
为什么这么难？ 只需使用java提供的ExecutorService。
如果你手工编写，你做错了。
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class Sample {
public static void main(String[] args) {
// configure here how many threads and other properties, the queue here is actually build in.
ExecutorService executor = Executors.newCachedThreadPool();
String[] arrayOfNames = { "alfred", "bob", "carl", "dave", "earl",
"fred", "greg", "harry", "izzie", "jim" };
for (int i = 0; i < arrayOfNames.length; i++) {
TheObject anObject = new TheObject(arrayOfNames[i], arrayOfNames[i].charAt(0), i);
MyRunnable runnalbe = new MyRunnable(anObject);
executor.execute(runnalbe);
}
executor.shutdown()
}
static class MyRunnable implements Runnable {
final TheObject anObject;
MyRunnable(TheObject theObject) {
this.anObject = theObject;
}
@Override
public void run() {
//TODO do work with anObject
}
}
static class TheObject {
private String someName;
private char someChar;
private int someNum;
public TheObject(String someName, char someChar, int someNum) {
this.someName = someName;
this.someChar = someChar;
this.someNum = someNum;
}
public String getSomeName() {
return someName;
}
public char getSomeChar() {
return someChar;
}
public int getSomeNum() {
return someNum;
}
}
}