java多线程锁同步控制

1、使用关键字：synchronized 

一、synchronized能够修饰方法，（其实也是锁的是当前方法的对象），也能够修饰代码块，修饰代码也须要传入一个对象。 synchronized(object){}

二、两种方式都是获取的是synchronized修饰对象的monitor锁!这才是真正的锁!

三、synchronized所修饰的锁不能够为null!

public class Main{
    private static int commonTag = 0;
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                while (true){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    add(Thread.currentThread().getId());

                }
            }
        };
        Thread t1 =  new Thread(runnable);
        Thread t2 =  new Thread(runnable);
        Thread t3 =  new Thread(runnable);
        Thread t4 =  new Thread(runnable);
        t1.start();
        t2.start();
        t3.start();
        t4.start();
    }

   public static synchronized void add(long ID){
        System.out.println("当前线程ID:"+ID+"执行结果="+commonTag++);
    }

//   public static  void add(long ID){
//        synchronized(object){  //也须要传入一个对象
//            System.out.println("当前线程ID:"+ID+"执行结果="+commonTag++);
//
//        }
//    }
}

当前线程ID:10执行结果=0
当前线程ID:11执行结果=1
当前线程ID:12执行结果=2
当前线程ID:13执行结果=3
当前线程ID:10执行结果=4
当前线程ID:12执行结果=5
当前线程ID:13执行结果=6
当前线程ID:11执行结果=7
当前线程ID:10执行结果=8
当前线程ID:13执行结果=9
当前线程ID:12执行结果=10
当前线程ID:11执行结果=11
当前线程ID:10执行结果=12
当前线程ID:13执行结果=13
当前线程ID:12执行结果=14
当前线程ID:11执行结果=15

若是不用则结果以下：

当前线程ID:12执行结果=3
当前线程ID:10执行结果=1
当前线程ID:13执行结果=2
当前线程ID:11执行结果=0
当前线程ID:12执行结果=5
当前线程ID:11执行结果=7
当前线程ID:13执行结果=6
当前线程ID:10执行结果=4
当前线程ID:11执行结果=8
当前线程ID:10执行结果=9
当前线程ID:13执行结果=9
当前线程ID:12执行结果=8

2、死锁的缘由和如何避免!

对于程序员须要关注两个方向：一个是内存不足引发的死锁，另外一个是交叉锁，各持对方的排它锁致使的死锁，谁都不愿放！

public class Main{
    private static int commonTag = 0;
    private static Object object1 = new Object();
    private static Object object2 = new Object();
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                while (true){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    add(Thread.currentThread().getId());

                }
            }
        };
        Runnable runnable2 = new Runnable() {
            @Override
            public void run() {
                while (true){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    add2(Thread.currentThread().getId());

                }
            }
        };

        Thread t1 =  new Thread(runnable);
        Thread t2 =  new Thread(runnable);
        Thread t3 =  new Thread(runnable2);
        Thread t4 =  new Thread(runnable2);
        t1.start();
        t2.start();
        t3.start();
        t4.start();
    }

   public static  void add(long ID){
        synchronized(object1){
            synchronized(object2){
                System.out.println("当前线程ID:"+ID+"执行结果="+commonTag++);

            }
        }
    }
    public static  void add2(long ID){
        synchronized(object2){
            synchronized(object1){
                System.out.println("当前线程ID:"+ID+"执行结果="+commonTag++);

            }
        }
    }

}

3、LOCK（java.util.concurrent.locks）

一、读写锁？

二、自旋锁

import java.util.concurrent.locks.ReentrantLock;
public class Main{
    private static int commonTag = 0;
    private  static ReentrantLock lock = new ReentrantLock();

    private static   Object object = new Object();
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                while (true){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    add(Thread.currentThread().getId());

                }
            }
        };
        Thread t1 =  new Thread(runnable);
        Thread t2 =  new Thread(runnable);
        Thread t3 =  new Thread(runnable);
        Thread t4 =  new Thread(runnable);
        t1.start();
        t2.start();
        t3.start();
        t4.start();
    }
   public static  void add(long ID){
        try{
            lock.lock();
            System.out.println("当前线程ID:"+ID+"执行结果="+commonTag++);
        }finally {
            lock.unlock();
        }

    }
}