手写了一个锁

尝试着用park+自旋手写实现一把锁

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
71
72
73
74
75
76
77
78
79
80
81
82
public class syncTest {
static volatile int status = 0;
static Queue<Thread> parkQueue = new LinkedList<>();

public static void main(String[] args) {
Thread t1 = new Thread(){
@Override
public void run() {
synctest();
}
};


Thread t2 = new Thread(){
@Override
public void run() {
synctest();
}
};

t1.setName("t1");
t2.setName("t2");
t1.start();
// try {
// Thread.sleep(2000);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
t2.start();

System.out.println("ThreadMain-----------");
}

//自旋 上锁 让出内存
public static void lock() {
while(!compareAndSet(0,1)){
park();
}
}
//唤醒
public static void unlock(){
status = 0;
lock_notify();
}
//阻塞线程并将阻塞线程写入队列
public static void park(){
parkQueue.offer(Thread.currentThread());
LockSupport.park();
}
//从队列里拿出线程并唤醒 再次尝试获得锁
private static void lock_notify() {
if(parkQueue.size() != 0){
Thread t = parkQueue.poll();
LockSupport.unpark(t);
}

}

private static boolean compareAndSet(int i, int j) {
if(status == i){
status = j;
return true;
}else{
return false;
}
}

//测试方法
public static void synctest() {
lock();
System.out.println(Thread.currentThread().getName() +"-------st");
try {
Thread.sleep(8000);
} catch (InterruptedException e) {
e.printStackTrace();
}

System.out.println(Thread.currentThread().getName() +"-------ed");
unlock();
}
}

查看评论