请看这段代码
public class Test extends Thread {
int i;
public Test(int i) {this.i = i;}
void simpleBlock() throws InterruptedException {
System.out.println(i + " this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.");
synchronized(this) {wait();}
}
public void run() {
try {simpleBlock();} catch (InterruptedException e) {}
}
}
这是由创建和启动线程的 Main 类实现的
public class Main {
public static void main(String[] args) throws InterruptedException {
Test[] t = new Test[20];
for (int i=0; i<20; i++) {
t[i] = new Test(i);
t[i].start();
}
}
}
这将打印以下输出
0 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
6 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
4 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
3 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
5 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
2 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
1 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
14 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
7 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
13 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
12 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
10 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
11 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
9 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
8 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
18 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
19 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
17 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
16 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
15 this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.
由于SimpleBlock()
不同步,我希望打印件会被随机切割。至少,这就是我不久前运行的另一个同步测试所发生的情况,除了那次我使用信号量(或缺少信号量)。
那么为什么每个线程都以如此有序的方式打印完整的字符串呢?
这将引导我进行下一个调查。
假设simpleBlock
是完全同步的,输出和上面一样。所以,
synchronized void simpleBlock() throws InterruptedException {
System.out.println(i + " this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.");
wait();
}
您可能已经知道,这相当于
void simpleBlock() throws InterruptedException {
synchronized(this) {
System.out.println(i + " this is an example of a thread blocking on itself - practicing concurrency 101, monitors, etc.");
this.wait();
}
}
我是否正确假设由于在上面的 Main 类中创建了 20 个线程,没有两个线程在共享对象上同步,因为每个线程都是它自己的唯一对象,因此,同步方案实际上会失败?
换句话说,创建许多线程,每个线程都在自己同步是不是一个坏主意?