这是来自Java 7 Concurrency cookbook的练习。目标是让多个生产者将事件写入共享队列,而清洁任务(守护程序线程)将从队列中删除超过5秒的事件。(查找下面的代码) 如果我尝试为此编写测试或在main()程序中使用它,它只需在队列中插入3个项目并退出。 我的问题:如果WriterTask中存在for循环,为什么程序不运行for循环(在队列中插入约30个项目)并在此之前退出?
import java.util.Date;
import java.util.Deque;
import java.util.concurrent.TimeUnit;
class Event{
Date var;
public Event(Date v){
var = v;
}
}
class WriterTask implements Runnable{
Deque<Event> queue;
int from = 0,to = 0;
public WriterTask(Deque<Event> queue, int from, int to){
this.queue = queue;
this.from = from;
this.to = to;
}
@Override
public void run(){
for(int i=from;i<to;i++){
Event ev = new Event(new Date());
System.out.println("Generating event number: "+i);
queue.addFirst(ev);
try{
System.out.println("SLeeping now:"+Thread.currentThread().getName());
TimeUnit.SECONDS.sleep(1);
}catch(InterruptedException ie){
System.out.println("Interrupted the thread!");
}
}
}
}
class CleanerTask implements Runnable{
Deque<Event> queue;
public CleanerTask(Deque<Event> queue){
this.queue = queue;
}
@Override
public void run(){
while(true){
Date dt = new Date();
clean(dt);
}
}
public void clean(Date date){
// System.out.println("Cleaning for date, current size of queue:"+queue.size());
long difference = 0;
boolean anythingDeleted = false;
do{
if(queue.isEmpty()){return;}
Event first = queue.getLast();
difference = date.getTime() - first.var.getTime();
if(difference > 5000){
queue.removeLast();
anythingDeleted = true;
}
}while(difference>5000);
if(anythingDeleted){
System.out.println("Queue cleaned up, new size:"+queue.size());
}
}
}
测试:
import org.junit.Test;
import org.junit.rules.Timeout;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.LinkedList;
public class WriterCleanerTest {
@Test
public void consumeCleanTest(){
Deque<Event> queue = new ArrayDeque<Event>();
WriterTask wt = new WriterTask(queue, 0, 10);
Thread wt1 = new Thread(wt);
Thread wt2 = new Thread(new WriterTask(queue, 60, 70));
Thread wt3 = new Thread(new WriterTask(queue, 100, 110));
wt1.start();
wt2.start();
wt3.start();
System.out.println("Size of queue:"+queue.size());
Thread cleanerTask = new Thread(new CleanerTask(queue));
cleanerTask.setDaemon(true);
cleanerTask.start();
}
}
输出:
Size of queue:0
Final Size of queue:0
Generating event number: 0
Generating event number: 60
SLeeping now:Thread-1
Generating event number: 100
SLeeping now:Thread-2
SLeeping now:Thread-0
Process finished with exit code 0
答案 0 :(得分:0)
您不是在等待线程完成。
在代码末尾添加:
cleanerTask.start();
// Wait for everything to finish.
wt1.join();
wt2.join();
wt3.join();
cleanerTask.join();
基本上你的主线程在退出之前必须join
所有其他正在运行的线程。