java -锁（公平、非公平锁、可重入锁【递归锁】、自旋锁）

1.公平锁、非公平锁

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2.可重入锁（递归锁）

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3.自旋锁

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AtomicReference atomicReference = new AtomicReference();//原子引用线程

下面代码5秒钟自旋了10万次，还是很消耗CPU的

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package HighConcurrency;import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;public class SpinLockDemo {//原子引用线程AtomicReference<Thread> atomicReference = new AtomicReference<>();public void myLock(){Thread thread = Thread.currentThread();System.out.println(Thread.currentThread().getName()+"\t come in");while(!atomicReference.compareAndSet(null,thread)){System.out.println(Thread.currentThread().getName()+"线程自旋。。。");}}public void myunLock(){Thread thread = Thread.currentThread();atomicReference.compareAndSet(thread,null);System.out.println(Thread.currentThread().getName()+"\t invoked myUnLock");}public static void main(String []args){SpinLockDemo spinLockDemo = new SpinLockDemo();new Thread(()->{spinLockDemo.myLock();//暂停线程一会try {TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); }spinLockDemo.myunLock();},"AA").start();try {TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); }new Thread(()->{spinLockDemo.myLock();spinLockDemo.myunLock();},"BB").start();}
}

4.独占锁(写锁)|共享锁(读锁)

独占锁：指该锁一次只能被一个线程持有，ReentrantLock和synchronized都是独占锁
共享锁：可被多个线程所持有。对ReentrantReadWriteLock其读锁是共享锁，其写锁是独占锁。
读锁的共享锁可保证高并发读是非常都效的

class MyCache{ //资源类private volatile Map<String,Object> map = new HashMap<>();private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();//写缓存框架，读、写、清空public void get(String key,Object value){ //读rwLock.readLock().lock();try {System.out.println(Thread.currentThread().getName() + "\t 正在读取：");try { TimeUnit.MILLISECONDS.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); }Object object = map.get(key);System.out.println(Thread.currentThread().getName() + "\t 读取完成" + object);}catch (Exception e){e.printStackTrace();}finally {rwLock.readLock().unlock();}}public void put(String key,Object value){ //写rwLock.writeLock().lock();try {System.out.println(Thread.currentThread().getName()+"\t 正在写入" + key);try { TimeUnit.MILLISECONDS.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); }System.out.println(Thread.currentThread().getName()+"\t 写入完成");}catch (Exception e){e.printStackTrace();}finally {rwLock.writeLock().unlock();}}}
public class ReadWriteLockDemo {public static void main(String[] args) {MyCache myCache = new MyCache();//线程操作资源类for (int i = 0; i < 5; i++) {final int tempInt = i;new Thread(() -> {myCache.put(tempInt+"",tempInt+"");},"线程"+String.valueOf(i)).start();}for (int i = 0; i < 5; i++) {final int tempInt = i;new Thread(() -> {myCache.get(tempInt+"",tempInt+"");},"线程"+String.valueOf(i)).start();}}
}