Java 學習筆記之 線程Priority

線程Priority:

 

線程可以划分優先級，優先級較高的線程得到的CPU資源較多，也就是CPU優先執行優先級較高的線程對象中的任務。

設置線程優先級有助於幫助“線程規划器”確定在下一次選擇哪個線程來優先執行。

線程優先級分為10個等級，1-》10

三個常用等級：

線程優先級繼承性：

A線程啟動了B線程，則B線程的優先級與A線程是一樣的。

public class PriorityInheritThread extends Thread {
    @Override
    public void run() {
        System.out.println("1 Run priority = " +  this.getPriority());
        PriorityInheritThread2 thread2 = new PriorityInheritThread2();
        thread2.start();
    }
}

public class PriorityInheritThread2 extends Thread{
    @Override
    public void run() {
        System.out.println("2 Run priority = " +  this.getPriority());
    }
}
public class ThreadRunMain {
    public static void main(String[] args) {
        testPriorityInheritThread();
    }

    public static void testPriorityInheritThread() {
        System.out.println("Main thread begin priority = " + Thread.currentThread().getPriority());
        Thread.currentThread().setPriority(6);
        System.out.println("Main thread end priority = " + Thread.currentThread().getPriority());
        PriorityInheritThread thread1 = new PriorityInheritThread();
        thread1.start();
    }
}

運行結果：

線程規則性：

優先級高的線程總是大部分先執行完。

線程隨機性：

當線程優先等級差距很大，誰先執行完和Main線程代碼的調用順序無關。優先級高的線程也不一定每一次都先執行完。

public class RunFastThreadA extends Thread {
    private int count = 0;

    public int getCount() {
        return count;
    }

    @Override
    public void run() {
        while(true){
            count ++;
        }
    }
}

public class RunFastThreadB extends Thread {
    private int count = 0;

    public int getCount() {
        return count;
    }

    @Override
    public void run() {
        while(true){
            count ++;
        }
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testRunFastThread();
    }

    public static void testRunFastThread() {
        try {
            RunFastThreadA a = new RunFastThreadA();
            a.setPriority(Thread.NORM_PRIORITY - 3);
            a.start();
            RunFastThreadB b = new RunFastThreadB();
            b.setPriority(Thread.NORM_PRIORITY + 3);
            b.start();
            Thread.sleep(10000);
            a.stop();
            b.stop();
            System.out.println("a = " + a.getCount());
            System.out.println("b = " + b.getCount());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

運行結果：