Java多线程基础 - 线程相关信息的操作

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在更深入地学习Java多线程之前，我们必须熟练有关Thread类的某些获取或设置线程相关信息的方法才行。

有关线程的信息，对于我们日常开发比较重要的也就那几个。线程名、线程ID、线程的优先级、线程的状态。这里就以一个简单的程序打印线程的各种信息。

首先，先来看任务类Task的代码。

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public class Task implements Runnable {
    private long duration = 0L;

    public Task() { }

    public Task(long duration) {
        this.duration = duration;
    }
	
    @Override
    public void run() {
        long begin = System.currentTimeMillis();
        while (System.currentTimeMillis() - begin <= duration) { }
        try {
            Thread.sleep(200);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

这里，我给任务类Task指定了一个域duration存储一个毫秒数，它表示执行该任务的所需时间，默认值是0，但这里也可以通过构造函数指定duration具体的毫秒数是多少。在run方法里，使用一个循环模拟任务的执行，经过duration毫秒后，该循环就会终止。然后，再让执行该任务的线程睡眠200毫秒。任务执行的整个过程如上所述。

而打印线程相关信息的程序代码如下。

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public class MainThread2 {
    private static final int SIZE = 10;
    private static Formatter f = new Formatter(System.out);
	
    public static void main(String[] args) {
        // 1.创建一个可以容纳10个线程对象的数组
        Thread[] threads = new Thread[SIZE];
        // 2. 初始化(设置线程的优先级以及线程名)
        for (int i = 0; i < SIZE; i++) {
            threads[i] = new Thread(new Task(2000));
            if (i % 2 == 0)
                threads[i].setPriority(Thread.MAX_PRIORITY);
            else
                threads[i].setPriority(Thread.MIN_PRIORITY);
            if (i == 7)
                threads[i].setPriority(Thread.NORM_PRIORITY);
            if (i % 3 == 0)
                threads[i].setName("Thread#" + i);
        }
    		
        // 3.创建一个保存线程数组中每个线程对应的线程状态
        Thread.State[] prevStates = new Thread.State[SIZE];
        for (int i = 0; i < SIZE; i++) {
            prevStates[i] = threads[i].getState();
        }        

        // 4.启动所有线程
        for (int i = 0; i < SIZE; i++)
            threads[i].start();        

        printTitle();
    		
        // 5.循环检测所有线程是否运行完毕
        boolean isFinish = false;
        while (!isFinish) {
            for (int i = 0; i < SIZE; i++) {
                if (threads[i].getState() != prevStates[i]) {
                    printThreadInfo("main", threads[i], prevStates[i]);
                    prevStates[i] = threads[i].getState();
                }
            }
            isFinish = true;
            for (int i = 0; i < SIZE; i++) {
                isFinish = isFinish && (threads[i].getState() == Thread.State.TERMINATED);
            }
        }
    }
	
    public static void printTitle() {
        f.format("%-10s %-12s %-3s %-8s %-13s %-14s\n",
            "method", "name", "id", "priority", "current state", "previous state");
        f.format("%-10s %-12s %-3s %-8s %-13s %-14s\n", 
            "------", "----", "--", "--------", "-------------", "--------------");
    }
	
    public static void printThreadInfo(String method, Thread thread, Thread.State prevState) {
        f.format("%-10s %-12s %-3d %-8d %-13s %-14s\n", method, thread.getName(),
            thread.getId(), thread.getPriority(), thread.getState(), prevState);
    }
}

运行后的打印结果：

method     name         id  priority current state previous state
------     ----         --  -------- ------------- --------------
main       Thread#0     9   10       RUNNABLE      NEW           
main       Thread-1     10  1        RUNNABLE      NEW           
main       Thread-2     11  10       RUNNABLE      NEW           
main       Thread#3     12  1        RUNNABLE      NEW           
main       Thread-4     13  10       RUNNABLE      NEW           
main       Thread-5     14  1        RUNNABLE      NEW           
main       Thread#6     15  10       RUNNABLE      NEW           
main       Thread-7     16  5        RUNNABLE      NEW           
main       Thread-8     17  10       RUNNABLE      NEW           
main       Thread#9     18  1        RUNNABLE      NEW           
main       Thread#0     9   10       TIMED_WAITING RUNNABLE      
main       Thread-1     10  1        TIMED_WAITING RUNNABLE      
main       Thread-2     11  10       TIMED_WAITING RUNNABLE      
main       Thread#3     12  1        TIMED_WAITING RUNNABLE      
main       Thread-4     13  10       TIMED_WAITING RUNNABLE      
main       Thread-5     14  1        TIMED_WAITING RUNNABLE      
main       Thread#6     15  10       TIMED_WAITING RUNNABLE      
main       Thread-7     16  5        TIMED_WAITING RUNNABLE      
main       Thread-8     17  10       TIMED_WAITING RUNNABLE      
main       Thread#9     18  1        TIMED_WAITING RUNNABLE      
main       Thread#0     9   10       BLOCKED       TIMED_WAITING 
main       Thread-1     10  1        TERMINATED    TIMED_WAITING 
main       Thread-2     11  10       TERMINATED    TIMED_WAITING 
main       Thread#3     12  1        TERMINATED    TIMED_WAITING 
main       Thread-4     13  10       TERMINATED    TIMED_WAITING 
main       Thread-5     14  1        TERMINATED    TIMED_WAITING 
main       Thread#6     15  10       TERMINATED    TIMED_WAITING 
main       Thread-7     16  5        TERMINATED    TIMED_WAITING 
main       Thread-8     17  10       TERMINATED    TIMED_WAITING 
main       Thread#9     18  1        TERMINATED    TIMED_WAITING

运行结果并不是固定不变的，每次运行结果都不太一样。

在程序中，这几个重要的方法都演示到了：

  • 通过Thread的setName设置线程的线程名，以及getName获取线程名。
  • 通过Thread的getId获取线程的id。
  • 通过Thread的setPriority设置线程的优先级，以及getPriority获取线程的优先级。
  • 通过Thread的getState获取线程的状态，但并没有提供对应的set方法给我们设置线程的状态，毕竟线程的调度都是由线程调度器决定的。