JAVA多线程之优先级设置线程特性

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我是靠谱客的博主无情汉堡，这篇文章主要介绍JAVA多线程之优先级设置线程特性，现在分享给大家，希望可以做个参考。

JAVA多线程之设置线程的优先级

线程特性
- setPriority()方法

线程特性

在操作系统中，线程可以划分优先级，优先级较高的线程得到的CPU资源要多一些，也就是CPU优先执行优先级较高的线程对象中的任务，其实就是让高优先级的线程获得更多的CPU时间片,但只是高优先级的线程获取资源的概率会大一点，并不一定保证一定就最先执行，这个取决于CPU

setPriority()方法

此方法在JDK中的源码如下

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/**
     * Changes the priority of this thread.
     * <p>
     * First the <code>checkAccess</code> method of this thread is called
     * with no arguments. This may result in throwing a
     * <code>SecurityException</code>.
     * <p>
     * Otherwise, the priority of this thread is set to the smaller of
     * the specified <code>newPriority</code> and the maximum permitted
     * priority of the thread's thread group.
     *
     * @param newPriority priority to set this thread to
     * @exception  IllegalArgumentException  If the priority is not in the
     *               range <code>MIN_PRIORITY</code> to
     *               <code>MAX_PRIORITY</code>.
     * @exception  SecurityException  if the current thread cannot modify
     *               this thread.
     * @see        #getPriority
     * @see        #checkAccess()
     * @see        #getThreadGroup()
     * @see        #MAX_PRIORITY
     * @see        #MIN_PRIORITY
     * @see        ThreadGroup#getMaxPriority()
     */
    public final void setPriority(int newPriority) {
        ThreadGroup g;
        checkAccess();
        if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
            throw new IllegalArgumentException();
        }
        if((g = getThreadGroup()) != null) {
            if (newPriority > g.getMaxPriority()) {
                newPriority = g.getMaxPriority();
            }
            setPriority0(priority = newPriority);
        }
    }

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/**
     * Changes the priority of this thread.
     * <p>
     * First the <code>checkAccess</code> method of this thread is called
     * with no arguments. This may result in throwing a
     * <code>SecurityException</code>.
     * <p>
     * Otherwise, the priority of this thread is set to the smaller of
     * the specified <code>newPriority</code> and the maximum permitted
     * priority of the thread's thread group.
     *
     * @param newPriority priority to set this thread to
     * @exception  IllegalArgumentException  If the priority is not in the
     *               range <code>MIN_PRIORITY</code> to
     *               <code>MAX_PRIORITY</code>.
     * @exception  SecurityException  if the current thread cannot modify
     *               this thread.
     * @see        #getPriority
     * @see        #checkAccess()
     * @see        #getThreadGroup()
     * @see        #MAX_PRIORITY
     * @see        #MIN_PRIORITY
     * @see        ThreadGroup#getMaxPriority()
     */
    public final void setPriority(int newPriority) {
        ThreadGroup g;
        checkAccess();
        if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
            throw new IllegalArgumentException();
        }
        if((g = getThreadGroup()) != null) {
            if (newPriority > g.getMaxPriority()) {
                newPriority = g.getMaxPriority();
            }
            setPriority0(priority = newPriority);
        }
    }

在这里插入图片描述
可以看到注释：更改线程的优先级有预定义几个优先级MIN_PRIORITY -到MAX_PRIORITY之间
也就是优先级分为1-10个等级，如果不在这个范围内则抛出异常IllegalArgumentException
一下是默认设置的几个级别：1、5、10 1最低，10最高，如果不设置，默认是5

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/**
     * The minimum priority that a thread can have.
     */
    public final static int MIN_PRIORITY = 1;

   /**
     * The default priority that is assigned to a thread.
     */
    public final static int NORM_PRIORITY = 5;

    /**
     * The maximum priority that a thread can have.
     */
    public final static int MAX_PRIORITY = 10;

但线程并不一定会按照这个优先级区执行，只是设置了优先级高的线程获取CUP资源的概率会大一点，但并不能保证百分百就是高优先级的线程最先执行
例如

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 public static void main(String[] arg){
        MyThread myThread = new MyThread("A");
        myThread.setPriority(1);
        MyThread myThread2 = new MyThread("B");
        myThread2.setPriority(10);
        MyThread myThread3 = new MyThread("C");
        myThread.start();
        myThread2.start();
        myThread3.start();
    }



    static class MyThread extends Thread{
        public MyThread(String name){
            super(name);
        }

        @Override
        public void run() {
            for (int i = 0 ;i<10; i++){
                System.out.println(i+"<------------->"+Thread.currentThread().getName());
            }
        }
    }

结果

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0<------------->B
0<------------->C
1<------------->C
2<------------->C
3<------------->C
0<------------->A
4<------------->C
5<------------->C
6<------------->C
7<------------->C
8<------------->C
9<------------->C
1<------------->B
2<------------->B
3<------------->B
4<------------->B
5<------------->B
1<------------->A
6<------------->B
7<------------->B
8<------------->B
9<------------->B
2<------------->A
3<------------->A
4<------------->A
5<------------->A
6<------------->A
7<------------->A
8<------------->A
9<------------->A

可以从结果看到A,B,C是交互执行，但B和C执行的顺序会在A前面（这个并不是百分百一点的）,但这个执行结果C的执行顺序要高于B,再次执行

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0<------------->B
1<------------->B
2<------------->B
3<------------->B
4<------------->B
5<------------->B
6<------------->B
7<------------->B
8<------------->B
9<------------->B
0<------------->C
1<------------->C
2<------------->C
3<------------->C
4<------------->C
5<------------->C
6<------------->C
7<------------->C
8<------------->C
9<------------->C
0<------------->A
1<------------->A
2<------------->A
3<------------->A
4<------------->A
5<------------->A
6<------------->A
7<------------->A
8<------------->A
9<------------->A