【Java】线程状态

1、线程状态 

初始-NEW: Thread : 对象已经创建，但start 方法还没调用.

终止-TERMINATED: Thread 对象还在,内核中的线程已经没了

运行-RUNNABLE: 就绪状态(线程已经在 cpu 上执行了/线程正在排队等待上 cpu 执行)

超时等待-TIMED WAITING: 阻塞.由于 sleep 这种固定时间的方式产生的阻塞.

等待-WAITING: 阻塞.由于 wait 这种不固定时间的方式产生的阻塞.

阻塞-BLOCKED:阻塞.由于锁竞争导致的阻塞.（死锁）

2、NEW、RUNNABLE、TERMINATED

我们通过getState()这个方法来获取线程状态

public class demo {
    public static void main(String[] args) {
        Thread thread = new Thread(()->{
            System.out.println("线程正在执行");
        });
 
        System.out.println(thread.getState());
        thread.start();
        System.out.println(thread.getState());
        try {
            thread.join();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("main线程执行");
        System.out.println(thread.getState());
 
    }
}

获取状态如下 

3、BLOCKIED-阻塞 

 BLOCKED是由于线程竞争发生死锁而导致的状态

下面这段代码就会发生死锁

public class demo {
    public static void main(String[] args) {
        Object locker1 = new Object();
        Object locker2 = new Object();
 
        Thread thread1 = new Thread(()->{
            synchronized (locker1){
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
 
                synchronized (locker2){
                    System.out.println("线程1进行了加锁");
                }
            }
        });
 
        Thread thread2 = new Thread(()->{
            synchronized (locker2){
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
 
                synchronized (locker1){
                    System.out.println("线程2进行了加锁");
                }
            }
        });
 
        thread1.start();
        thread2.start();
    }
}

通过jconsole查看线程状态，可知线程1、2都进入了BLOCKED状态 

 

4、WAITING状态

调用wait()方法，还未唤醒时，线程就处于WAITING状态

public class demo {
    public static void main(String[] args) {
        Object object = new Object();
        Thread thread1 = new Thread(()->{
            synchronized (object){
                try {
                    object.wait();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        });
 
        Thread thread2 = new Thread(()->{
            synchronized (object){
                object.notify();
            }
        });
 
        thread1.start();
        System.out.println(thread1.getState());
        thread2.start();
 
    }
}

查看状态