一个快速(我认为)并发问题:我正在Udemy.com上通过一个多线程课程,老师通过下面的代码进行了讨论。虽然他解释了它,但我仍不确定为什么要创建lock1
和lock2
对象而不是锁定在list1
和list2
上。同步:多重锁定 - 创建锁定对象?
App.java:
public class App {
public static void main(String[] args) {
Worker worker = new Worker();
worker.main();
}
}
Worker.java:
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class Worker {
private Random random = new Random();
private Object lock1 = new Object();
private Object lock2 = new Object();
private List<Integer> list1 = new ArrayList<Integer>();
private List<Integer> list2 = new ArrayList<Integer>();
public void stageOne() {
synchronized (lock1) {
try {
Thread.sleep(1);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
list1.add(random.nextInt(100));
}
}
public void stageTwo() {
synchronized (lock2) {
try {
Thread.sleep(1);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
list2.add(random.nextInt(100));
}
}
public void process() {
for(int i=0; i<1000; i++) {
stageOne();
stageTwo();
}
}
public void main() {
System.out.println("Starting ...");
long start = System.currentTimeMillis();
Thread t1 = new Thread(new Runnable() {
public void run() {
process();
}
});
Thread t2 = new Thread(new Runnable() {
public void run() {
process();
}
});
t1.start();
t2.start();
try {
t1.join();
t2.join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
long end = System.currentTimeMillis();
System.out.println("Time taken: " + (end - start));
System.out.println("List1: " + list1.size() + "; List2: " + list2.size());
}
}
没有理由。你应该只能在'final'变量上同步。如果你可以将你的'List'标记为'final',那么你可以简单地同步它。使用单独的对象可以分离关注点,并可以考虑使代码更清晰。 – 2014-09-29 11:42:54
同意鲍里斯。有一点我会添加它,你永远不想锁定由getter返回的字段。因此,通过将锁定与用于不同目的的任何字段隔离,可以消除这种可能性。 – 2014-09-29 11:47:22
感谢@BoristheSpider和@John B.为什么只锁定'final'变量?为什么不使用getters? – 2014-09-29 12:10:28