线程 同步 死锁

7 线程  Thread   

1）线程和进程的区别：线程是比进程更小的单位，一个线程就是一个在CPU队里排队的任务

2）run 和 start的区别，run方法只是做简单的方法调用，不能开启一个新的时间分支，start可以开启一个新的线程

3）创建线程的两种方式：

  （1）继承Thread类，并重写run方法

//main主线程 public static void main(String[] args) { //start进行多任务，并行执行,开启一个新线程 // MyThread01 th01=new MyThread01(); // th01.run();//阻塞式执行 //// th01.start();

//将该线程要执行的代码放在run里 public class MyThread01 extends Thread { @Override public void run() { for(int i=0;i<1000;i++){ System.out.println("------------------"); } } }

 

  （2）实现Runnable接口，并重新run方法（可以实现多继承）

//// MyThread04 th04=new MyThread04(); //// Thread th=new Thread(th04); //// th.start();

public class MyThread04 implements Runnable { @Override public void run() { for (int i=0;i<1000;i++){ System.out.println("========"); } } }

 

两种方法的区别：只有Thread和他的子类有start方法

public class ThreadForTime implements Runnable { boolean flag=true;//标志位 public boolean isFlag() { return flag; } public void setFlag(boolean flag) { this.flag = flag; } @Override public void run() { SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); while (flag){ System.out.println(sdf.format(new Date())); try { Thread.sleep(1000);//相当于睡眠状态，不出让cpu } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println("---------end-------"); } }

public class DemoForTime {//线程结束不能用stop public static void main(String[] args) { Scanner sc=new Scanner(System.in); ThreadForTime thread=new ThreadForTime(); Thread th=new Thread(thread); th.start(); String c=sc.next(); if("0".equals(c)){ thread.setFlag(false); } } }

4）线程同步（synchronized）：确保一段代码在执行时，不被其他线程打乱
   (1)同步方法

public class Th02 implements Runnable { int count=0; Boolean flag=true; @Override public void run() { while (flag) { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } sale(); } } public synchronized void sale () { if (count <= 100) { System.out.println(Thread.currentThread() + ":" + count); count++; } else { flag = false; } } }

Th02 th=new Th02(); Thread thread=new Thread(th); thread.start(); Thread thread1=new Thread(th); thread1.start();

   (2)同步代码块

public class ThreadForClock implements Runnable { boolean flag=true; int count=0; boolean isSuspend=false; Object ob=new Object(); @Override public void run() { while (flag){ synchronized (ob){//括号里任意一个对象 try { Thread.sleep(1000); count++; System.out.println(count); if(isSuspend){ ob.wait(); } } catch (InterruptedException e) { e.printStackTrace(); } } } System.out.println("-----end-----"); } public void resume(){ synchronized (ob){ ob.notifyAll(); } } public boolean isFlag() { return flag; } public void setFlag(boolean flag) { this.flag = flag; } public int getCount() { return count; } public void setCount(int count) { this.count = count; } public boolean isSuspend() { return isSuspend; } public void setSuspend(boolean suspend) { isSuspend = suspend; } public Object getOb() { return ob; } public void setOb(Object ob) { this.ob = ob; } }

public class DemoForClock { public static void main(String[] args) { Scanner sc=new Scanner(System.in); System.out.println("1 start 2 suspend 3resume 4stop"); ThreadForClock th=new ThreadForClock(); Thread thread=new Thread(th); while (true){ String c=sc.next(); if("1".equals(c)){ thread.start(); } else if("2".equals(c)){ th.isSuspend=true; } else if("3".equals(c)){ th.isSuspend=false; th.resume(); } else if("4".equals(c)){ th.setFlag(false); break; } } } }

   5）线程通信:  wait（让线程等待一段时间，出让资源）  notify(唤醒指定一个线程)    notifyAll（唤醒所有线程）都是Object的方法，这三个方法只能用在线程同步里，在线程同步方法或者同步代码块外都不能用

  6）死锁：线程同步里

public class ThreadForDeadLock implements Runnable {//加static保证一个类 两个静态对象 private static Object o1=new Object(), o2=new Object(),o3=new Object(); private int threadCode; public ThreadForDeadLock(int threadCode) { this.threadCode = threadCode; } @Override public void run() { System.out.println(Thread.currentThread()+"is running"); if(threadCode==1){ synchronized (o1){//synchronized (o1)锁上了O1 System.out.println(Thread.currentThread()+"获取了o1资源"); try { //当代码块里所有代码都执行完O1才能被释放 Thread.sleep(1000);//线程启动不能控制线程速度 } catch (InterruptedException e) { e.printStackTrace(); } synchronized (o2){//解锁synchronized (o3) O1执行完释放 System.out.println(Thread.currentThread()+"获取了o2资源"); } } } if(threadCode==2){ synchronized (o2){//锁上了O2 System.out.println(Thread.currentThread()+"获取了o2资源"); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } synchronized (o1){ System.out.println(Thread.currentThread()+"获取了o1资源"); } } } }

ThreadForDeadLock th=new ThreadForDeadLock(1); ThreadForDeadLock th1=new ThreadForDeadLock(2); Thread thread=new Thread(th); thread.start(); Thread thread1=new Thread(th1); thread1.start(); class ThreadForDeadLock类里 ： public static Object getO1() { return o1; } public static void setO1(Object o1) { ThreadForDeadLock.o1 = o1; } public static Object getO2() { return o2; } public static void setO2(Object o2) { ThreadForDeadLock.o2 = o2; } public int getThreadCode() { return threadCode; } public void setThreadCode(int threadCode) { this.threadCode = threadCode; } }