Java常见面试题之多线程和高并发详解

class MyData {
 //volatile int number = 0;//case2
 //int number=0; //case1
 public void change() {
 number = 60;
 }
}

public class VolatileDemo {
 public static void main(String[] args) {
 MyData data=new MyData();

 new Thread(()->{
 System.out.println(Thread.currentThread().getName()+"\t come in");
 try{ TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) {e.printStackTrace();}
 data.change();
 System.out.println(Thread.currentThread().getName()+"\t updated number value:"+data.number);
 },"A").start();

 while(data.number==0){}
 System.out.println(Thread.currentThread().getName()+"\t over, get number:"+data.number);

 }
}

class MyData {
 volatile int number = 0;

 public void change() {
 number = 60;
 }

 public void addOne() {
 number++;
 }
}

public class VolatileDemo {
 public static void main(String[] args) {
 case2();
 }

 //验证原子性
 public static void case2() {
 MyData myData = new MyData();

 for (int i = 0; i < 20; i++) {
 new Thread(() -> {
 for (int j = 0; j < 1000; j++) {
  myData.addOne();
 }
 }, String.valueOf(i)).start();
 }

 while(Thread.activeCount()>2){
 Thread.yield();
 }
 System.out.println(Thread.currentThread().getName()+"\t number value:"+myData.number);
 }
}

public class Singleton {

 private static Singleton instance=null;
 private Singleton(){
 System.out.println(Thread.currentThread().getName()+" constructor");
 }

 //DCL 双端检锁机制
 public static Singleton getInstance(){
 if(instance==null){
 synchronized (Singleton.class){
 if(instance==null)
  instance=new Singleton();
 }
 }
 return instance;
 }
}

private static volatile Singleton instance = null;

//AtomicInteger i++
public final int getAndIncrement(){
 return unsafe.getAndAddInt(this,valueoffset,1);
}

//AtomicInteger.java
private static final Unsafe unsfae=Unsafe.getUnsafe();//unsafe对象
private static final long valueOffset;//地址偏移量

static{
 try{
 valueoffset=unsafe.objectFieldOffset(AtomicInteger.class.getDeclaredField("value");
 }catch(Excepthion ex){throw new Error(ex);}
}

private volatile int value;//存储的数值

//unsafe.getAndAddInt
public final int getAndAddInt(Object var1,long var2,int var4){
 int var5;
 do{
 //获取当前的值的地址
 var5=this.getIntVolatile(var1,var2);
 //var1代表对象，var2和var5分别代表当前对象的真实值和期望值，如果二者相等，更新为var5+var4
 }while(!this.compareAndSwapInt(var1,var2,var5,var5+var4);
 return var5;
}

public class SolveABADemo {
 static AtomicStampedReference<Integer> atomicStampedReference=new AtomicStampedReference<>(100,1);

 new Thread(()->{
 int stamp=atomicStampedReference.getStamp();
 System.out.println(Thread.currentThread().getName()+"\t 版本号："+stamp);
 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 atomicStampedReference.compareAndSet(100,101,atomicStampedReference.getStamp(),atomicStampedReference.getStamp()+1);
 System.out.println(Thread.currentThread().getName()+"\t 版本号："+atomicStampedReference.getStamp());
 atomicStampedReference.compareAndSet(101,100,atomicStampedReference.getStamp(),atomicStampedReference.getStamp()+1);
 System.out.println(Thread.currentThread().getName()+"\t 版本号："+atomicStampedReference.getStamp());
 },"t1").start();

 new Thread(()->{
 int stamp=atomicStampedReference.getStamp();
 System.out.println(Thread.currentThread().getName()+"\t 版本号："+stamp);
 try {
 Thread.sleep(3000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 boolean ret=atomicStampedReference.compareAndSet(100,2019,stamp,stamp+1);
 System.out.println(Thread.currentThread().getName()+"\t"+ret
 +" stamp:"+atomicStampedReference.getStamp()
 +" value:"+atomicStampedReference.getReference());
 },"t2").start();
 }
}

public boolean add(E e){
 final ReentrantLock lock=this.lock;
 try{
 //旧数组
 Object[] elements = getArray();
 int len = elements.length;
 //复制新数组
 Object[] newElements = Arrays.copyOf(elements, len+1);
 //修改新数组
 newElements[len] = e;
 //更改旧数组引用指向新数组
 setArray(newElements);
 return true;
 }finally{
 lock.unlock();
 }
}

public class SpinLockDemo {
//使用AtomicReference<Thread>来更新当前占用的 Thread
 AtomicReference<Thread> threadAtomicReference=new AtomicReference<>();

 public static void main(String[] args) {
 SpinLockDemo demo=new SpinLockDemo();
 new Thread(()->{
 demo.myLock();
 try {
 Thread.sleep(3000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 demo.myUnlock();
 },"t1").start();


 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }

 new Thread(()->{
 demo.myLock();
 demo.myUnlock();
 },"t2").start();

 }

 public void myLock(){
 Thread thread=Thread.currentThread();
 System.out.println(Thread.currentThread().getName()+"\t come in");
 
 //如果当前占用的线程为null，则尝试获取更新
 while(!threadAtomicReference.compareAndSet(null,thread)){

 }
 }

 public void myUnlock(){
 Thread thread=Thread.currentThread();
 //释放锁，将占用的线程设置为null
 threadAtomicReference.compareAndSet(thread,null);
 System.out.println(Thread.currentThread().getName()+"\t unlocked");
 }
}

class ShareData {
 private int number = 0;
 private Lock lock = new ReentrantLock();
 private Condition condition = lock.newCondition();

 public void increment() throws Exception {
 lock.lock();
 try {
 //判断
 while (number != 0) {
 condition.await();
 }
 //干活
 number++;
 System.out.println(Thread.currentThread().getName() + " produce\t" + number);
 //通知唤醒
 condition.signalAll();
 } catch (Exception e) {
 e.printStackTrace();
 } finally {
 lock.unlock();
 }
 }

 public void decrement()throws Exception{
 lock.lock();
 try {
 //判断
 while (number == 0) {
 condition.await();
 }
 //干活
 number--;
 System.out.println(Thread.currentThread().getName() + " consume\t" + number);
 //通知唤醒
 condition.signalAll();
 } catch (Exception e) {
 e.printStackTrace();
 } finally {
 lock.unlock();
 }
 }
}

/**
 * 一个初始值为0的变量，两个线程交替操作，一个加1一个减1,重复5次
 * 1. 线程 操作 资源类
 * 2. 判断 干活 通知
 * 3. 防止虚假唤醒机制:判断的时候要用while而不是用if
 */
public class ProduceConsumeTraditionalDemo {
 public static void main(String[] args) {
 ShareData data=new ShareData();

 new Thread(()->{
 for (int i = 0; i < 5 ; i++) {
 try {
  data.increment();
 } catch (Exception e) {
  e.printStackTrace();
 }
 }
 },"A").start();

 new Thread(()->{
 for (int i = 0; i < 5 ; i++) {
 try {
  data.decrement();
 } catch (Exception e) {
  e.printStackTrace();
 }
 }
 },"B").start();
 }
}

public class ProduceConsumeBlockingQueueDemo {
 public static void main(String[] args) {
 SharedData data=new SharedData(new ArrayBlockingQueue<>(10));
 new Thread(()-> {
  System.out.println(Thread.currentThread().getName() + "\t生产线程启动");
  try {
  data.produce();
  } catch (InterruptedException e) {
  e.printStackTrace();
  }
 },"Producer").start();
 new Thread(()-> {
  System.out.println(Thread.currentThread().getName() + "\t消费线程启动");
  try {
  data.consume();
  } catch (InterruptedException e) {
  e.printStackTrace();
  }
 },"Consumer").start();

 try {
  Thread.sleep(3000);
 } catch (InterruptedException e) {
  e.printStackTrace();
 }
 data.stop();
 System.out.println("停止");
 }
}

class SharedData{
 private volatile boolean FLAG=true;
 private AtomicInteger atomicInteger=new AtomicInteger();

 BlockingQueue<String> blockingQueue=null;

 public SharedData(BlockingQueue<String> blockingQueue) {
 this.blockingQueue = blockingQueue;
 System.out.println(blockingQueue.getClass().getName());
 }

 public void produce() throws InterruptedException {
 String data=null;
 boolean ret;
 while(FLAG){
  data=""+atomicInteger.incrementAndGet();
  ret=blockingQueue.offer(data,2L,TimeUnit.SECONDS);
  if(ret){
  System.out.println(Thread.currentThread().getName()+"\t插入"+data+"成功");
  }else{
  System.out.println(Thread.currentThread().getName()+"\t插入"+data+"失败");
  }
  TimeUnit.SECONDS.sleep(1);
 }
 System.out.println("生产结束，FLAG=false");
 }

 public void consume() throws InterruptedException {
 String ret=null;
 while(FLAG){
  ret=blockingQueue.poll(2L,TimeUnit.SECONDS);
  if(null==ret||ret.equalsIgnoreCase("")){
  System.out.println(FLAG=false);
  System.out.println(Thread.currentThread().getName()+"\t消费等待超时退出");
  return;
  }
  System.out.println(Thread.currentThread().getName() + "\t消费" + ret + "成功");
 }
 }

 public void stop(){
 FLAG=false;
 }
}

class ShareData{
 private int number=1;
 private Lock lock=new ReentrantLock();

 public void printA(){
 lock.lock();
 Condition conditionA=lock.newCondition();
 try{
  while(number!=1){
  conditionA.await();
  }
  for (int i = 0; i < 5; i++) {
  System.out.println(Thread.currentThread().getName()+"\t"+i);
  }
  number=2;
  conditionA.signal();
 }catch (Exception e){
  e.printStackTrace();
 } finally {
  lock.unlock();
 }
 }

 public void printB(){
 lock.lock();
 Condition conditionB=lock.newCondition();
 try{
  while(number!=2){
  conditionB.await();
  }
  for (int i = 0; i < 10; i++) {
  System.out.println(Thread.currentThread().getName()+"\t"+i);
  }
  number=3;
  conditionB.signal();
 }catch (Exception e){
  e.printStackTrace();
 } finally {
  lock.unlock();
 }
 }

 public void printC(){
 lock.lock();
 Condition conditionC=lock.newCondition();
 try{
  //判断
  while(number!=3){
  conditionC.await();
  }
  //干活
  for (int i = 0; i < 15; i++) {
  System.out.println(Thread.currentThread().getName()+"\t"+i);
  }
  number=1;
  //通知
  conditionC.signal();
 }catch (Exception e){
  e.printStackTrace();
 } finally {
  lock.unlock();
 }
 }

 public static void main(String[] args) {
 ShareData data=new ShareData();
 new Thread(() -> data.printA(),"A").start();
 new Thread(() -> data.printB(),"B").start();
 new Thread(() -> data.printC(),"C").start();
 }
}

class MyThread implements Callable<Integer>{
 @Override
 public Integer call() {
 System.out.println("come in callable");
 return 2019;
 }
}
class Main{
 public static void main(String [] args){
 FutureTask<Integer> futureTask = new FutureTask<>(new MyThread2());
 Thread t1=new Thread(futureTask,"A");
 }
}

public ThreadPoolExecutor(
 int corePoolSize,//线程池常驻核心线程数
 int maximumPoolSize,//线程池能容纳同时执行最大线程数
 long keepAliveTime,//多余的空闲线程的存活时间，当前线程池线程数量超过core，空闲时间达到keepAliveTime，多余空闲线程会被销毁直到只剩下core个
 TimeUnit unit,
 BlockingQueue<Runnable> workQueue,//被提交尚未被执行的任务队列
 ThreadFactory threadFactory,//创建线程的线程工厂
 RejectedExecutionHandler handler//拒绝策略
 ) 
{...}

return new ThreadPoolExecutor(nThreads, nThreads, 
 0L, TimeUnit.MILLISECONDS, 
 new LinkedBlockingQueue<Runnable>());

return new FinalizableDelegatedExecutorService
 (new ThreadPoolExecutor(1, 1,
  0L, TimeUnit.MILLISECONDS,
  new LinkedBlockingQueue<Runnable>()));

return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
  60L, TimeUnit.SECONDS,
  new SynchronousQueue<Runnable>());

class HoldLockThread implements Runnable{
 private String lock1;
 private String lock2;

 public HoldLockThread(String lock1, String lock2) {
  this.lock1 = lock1;
  this.lock2 = lock2;
 }

 @Override
 public void run() {
  synchronized (lock1){
   System.out.println(Thread.currentThread().getName()+"\t持有"+lock1+"\t尝试获取"+lock2);
   try {
    Thread.sleep(2000);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
   synchronized (lock2){
    System.out.println(Thread.currentThread().getName()+"\t持有"+lock1+"\t尝试获取"+lock2);
   }
  }
 }
}

public class DeadLockDemo {
 public static void main(String[] args) {
  String lockA="lockA";
  String lockB="lockB";

  new Thread(new HoldLockThread(lockA,lockB),"Thread1").start();
  new Thread(new HoldLockThread(lockB,lockA),"Thread2").start();
 }
}