自旋锁简介
- 是指尝试获取锁的线程不会立即阻塞，而是采用循环的方式尝试获取锁，这样的好处是减少线程上下文切换的消耗，缺点是循环会消耗CPU
代码实现自旋锁
public class SpinLock {
//原子引用线程
AtomicReference<Thread> atomicReference = new AtomicReference<Thread>();
public static void main(String[] args) {
SpinLock spinLock = new SpinLock();
new Thread(() -> {
spinLock.mylock();
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
spinLock.myUnlock();
},"AAA").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(() -> {
spinLock.mylock();
spinLock.myUnlock();
},"BBB").start();
}
public void mylock(){
Thread thread = Thread.currentThread();
System.out.println(Thread.currentThread().getName()+"\t come in ");
while (!atomicReference.compareAndSet(null,thread)){
//System.out.println("在等待: "+Thread.currentThread().getName());
};
}
public void myUnlock(){
Thread thread = Thread.currentThread();
atomicReference.compareAndSet(thread,null);
System.out.println(Thread.currentThread().getName()+"\t come out");
}
}
juc中自旋锁源码
atomicInteger.incrementAndGet();
public final int incrementAndGet() {
return unsafe.getAndAddInt(this, valueOffset, 1) + 1;
}
public final int getAndAddInt(Object var1, long var2, int var4) {
int var5;
do {
var5 = this.getIntVolatile(var1, var2);
} while(!this.compareAndSwapInt(var1, var2, var5, var5 + var4));
return var5;
}
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