友情支持

如果您觉得这个笔记对您有所帮助，看在D瓜哥码这么多字的辛苦上，请友情支持一下，D瓜哥感激不尽，😜

支付宝

微信

有些打赏的朋友希望可以加个好友，欢迎关注D 瓜哥的微信公众号，这样就可以通过公众号的回复直接给我发信息。

wx jikerizhi

公众号的微信号是: jikerizhi。因为众所周知的原因，有时图片加载不出来。 如果图片加载不出来可以直接通过搜索微信号来查找我的公众号。

42. LockSupport

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56

package com.diguage.truman.concurrent;

import org.junit.jupiter.api.Test;

import java.util.concurrent.locks.LockSupport;

/**
 * @author D瓜哥, https://www.diguage.com/
 * @since 2020-03-16 19:16
 */
public class LockSupportTest {
    @Test
    public void test() throws InterruptedException {
        Thread t1 = new Thread(new Task("t1"));
        Thread t2 = new Thread(new Task("t2"));
        t1.start();
        Thread.sleep(1000);
        t2.start();
        LockSupport.unpark(t1);
        LockSupport.unpark(t2);
        t1.join();
        t2.join();
        System.out.println("finish...");
    }

    static class Task implements Runnable {
        private String name;

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

        @Override
        public void run() {
            synchronized (LockSupportTest.class) {
                System.out.println("in " + name);
                LockSupport.park();
            }
        }
    }

    @Test
    public void testParkAndUnpark() throws InterruptedException {
        System.out.println("--m1------");
        Thread thread = new Thread(() -> {
            System.out.println("--t1------");
            LockSupport.park();
            System.out.println("--t2------");
        });
        thread.start();
        Thread.sleep(5000);
        LockSupport.unpark(thread);
        System.out.println("--m2------");
    }

}

synchronized 关键字在方法上使用时，在方法修饰符上增加了一个标志位 flags: (0x0021) ACC_PUBLIC, ACC_SYNCHRONIZED。而用在代码块时，则是生成了 monitorenter 和 monitorexit 指令。

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70

package com.diguage.truman.concurrent;

import org.junit.jupiter.api.Test;

import java.util.concurrent.locks.LockSupport;

/**
 * @author D瓜哥, https://www.diguage.com/
 * @since 2020-04-08 19:26
 */
public class SynchronizedTest {
  public synchronized void lockMethod() {
    System.out.println("lock method");
  }

  public void lockObject() {
    synchronized (this) {
      System.out.println("lock object");
    }
  }

  @Test
  public void testInstanceLock() {
    SynMain main = new SynMain();
    new Thread(main::getInstanceLock1).start();
    new Thread(main::getInstanceLock2).start();
    new Thread(SynMain::getStaticLock1).start();
    new Thread(SynMain::getStaticLock2).start();
    LockSupport.park();
  }


  public static class SynMain {
    public static synchronized void getStaticLock1() {
      System.out.println("getStaticLock1 get lock, running...");
      try {
        Thread.sleep(Integer.MAX_VALUE);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }

    public static synchronized void getStaticLock2() {
      System.out.println("getStaticLock2 get lock, running...");
      try {
        Thread.sleep(Integer.MAX_VALUE);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }

    public synchronized void getInstanceLock1() {
      System.out.println("getInstanceLock1 get lock, running...");
      try {
        Thread.sleep(Integer.MAX_VALUE);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }

    public synchronized void getInstanceLock2() {
      System.out.println("getInstanceLock2 get lock, running...");
      try {
        Thread.sleep(Integer.MAX_VALUE);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }
  }
}

可以利用 jclasslib Bytecode viewer 工具，或者 javap -c -v XXX.class 来查看。

← Previous: Thread | ↑ Up: JDK 源码分析 | Next: AbstractQueuedSynchronizer →