java 中的多个线程无法执行非同步代码

Question

如果 Thread1 获得锁并开始执行同步块，同时 Thread2 可以自由执行代码的非同步部分 IntStream.range(0, 5).forEach(x -> System.out.println("thread Unsafe Zone,"+name)).

出乎意料，下面是我运行代码时实际发生的事情。

说明-

假设，thread1(或thread2)获得锁并执行synchronized块，然后thread2(或thread1)获得thread1(或thread2)释放的锁并执行synchronized block.After两个线程完成执行同步块，然后两个线程并行开始执行非同步部分。我运行代码多次希望获得所需的输出但没有用。

演示 class

public class Demo {
    public static void main(String[] args) {

        Display d=new Display("AnyName");
        Thread1 t1=new Thread1(d);
        Thread2 t2=new Thread2(d);
        t1.start();
        t2.start();
    }
}

线程 1 class

public class Thread1 extends Thread {
    Display d;
    Thread1(Display d) {
        this.d = d;
    }
    @Override
    public void run() {
       d.getname("Thread 1");
    }
}

线程 2 class

public class Thread2 extends Thread {
    Display d;

    Thread2(Display d) {
        this.d = d;
    }

    @Override
    public void run() {
            d.getname("Thread 2");
    }
}

显示class

public class Display {
    String name;

    public Display(String name) {
        this.name = name;
    }

    public void getname(String name)  {
        synchronized (this) {
            IntStream.range(0, 5).forEach((idx) -> {
                System.out.println(name);
            });
            this.name=name;
        }

        IntStream.range(0, 5).forEach(x -> System.out.println("thread Unsafe Zone,"+name));// this line
//get executed only after the synchronized method completed by both thread

    }
}

输出：

Thread 2
Thread 2
Thread 2
Thread 2
Thread 2
Thread 1
Thread 1
Thread 1
Thread 1
Thread 1
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 2

Answer 1

如果Thread1拿到锁开始执行synchronized块，同时Thread2可以自由执行代码的非同步部分：不完全是。

在执行顺序上，非同步块在同步块之后。因此你永远不会看到任何线程在同步块之前执行非同步块。

你能期待的最好的事情就是

Thread 1
Thread 1
Thread 1
Thread 1
Thread 1
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 1
Thread 2
Thread 2
Thread 2
Thread 2
Thread 2
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 1
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 2
thread Unsafe Zone,Thread 2

线程2进入同步块，线程1运行进入非同步块

您可以通过在同步块之后调用 Thread.yield(); 并进行更多 System.out.println() 调用来更改 Display.getname() 方法，从而增加出现这种结果的机会：

public void getname(String name)  {
    synchronized (this) {
        IntStream.range(0, 5).forEach((idx) -> {
            System.out.println(name);
        });
        this.name=name;
    }
    Thread.yield();

    IntStream.range(0, 20).forEach(x -> System.out.println("thread Unsafe Zone,"+name));

}

java 中的多个线程无法执行非同步代码

Multiple thread failed to execute the nonsynchronized code in java

java

multithreading

synchronization