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  • 线程同步synchronized,Class与Object

    synchronized (class):class类的同步,同步的时候会同步整个class

    synchronized (Object):Object的同步,只对其中的对象同步

    如下:对类B中的同步代码块的同步,对比之后放可明白

    synchronized (MyThread.class)

    例:

    A:类UnsafeSequence

    public class UnsafeSequence {
        private static int value;
        
        public int getValue()
        {
            synchronized (UnsafeSequence.class) {
                return value++;
            }
        }
        
        public int getValueA()
        {
            synchronized (this) {
                return value++;
            }
        }
    }

    B:类MyThread

    public class MyThread implements Runnable {
        private UnsafeSequence unsafe;
        private static int value;
        
        @Override
        public void run() {
            unsafe = new UnsafeSequence();
            for(int i = 0; i < 60; i++)
            {
                synchronized (MyThread.class) {
                    System.out.println(Thread.currentThread().getName() + "----in:");
                    System.out.println(Thread.currentThread().getName() + " thread run i = " + i + ";value = " + unsafe.getValue());
                    System.out.println(Thread.currentThread().getName() + "----out:" + value++);
                }
            }
        }

    }

    C:主函数

    public class TestMain {
        public static void main(String[] args) {
            MyThread target_1 = new MyThread();
            MyThread target_2 = new MyThread();
            Thread thread_1 = new Thread(target_1, "A");
            Thread thread_2 = new Thread(target_2, "B");
            thread_1.start();
            thread_2.start();
        }
    }

    结果如下:

    B----in:
    B thread run i = 0;value = 0
    B----out:0
    B----in:
    B thread run i = 1;value = 1
    B----out:1
    B----in:
    B thread run i = 2;value = 2
    B----out:2

    去掉B中的同步,或换为Object,结果如下:

    A----in:
    B----in:
    A thread run i = 0;value = 0
    B thread run i = 0;value = 1
    A----out:0
    B----out:1
    A----in:
    B----in:
    A thread run i = 1;value = 2
    B thread run i = 1;value = 3
    B----out:3
    B----in:
    A----out:2

    控制同步:

    public class MyThread implements Runnable {
        private UnsafeSequence unsafe;
        private static int value;
        
        @Override
        public void run() {
            synchronized (MyThread.class) {
                unsafe = new UnsafeSequence();
                for(int i = 0; i < 60; i++)
                {
                    System.out.println(Thread.currentThread().getName() + "----in:");
                    System.out.println(Thread.currentThread().getName() + " thread run i = " + i + ";value = " + unsafe.getValue());
                    System.out.println(Thread.currentThread().getName() + "----out:" + value++);
                }
            }
        }
    }

    我很小我很弱,我在慢慢成长!
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  • 原文地址:https://www.cnblogs.com/lvzhanhui/p/lvzhanhui.html
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