Java并发编程之：ThreadGroup

线程组ThreadGroup标识一组线程的集合，一旦一个线程归属到一个线程组中，就不能更换其所在的线程组。

使用线程组好处：方便统一管理，线程组合一进行复制，快读定位到一个线程，统一进行一场设置等。

ThreadGroup并不属于java并发包中的内容，它是java.lang中的内容。

基本方法：

1.获取当前线程组名：

Thread.currentThread().getThreadGroup().getName();

在main方法中输出main

2.将线程放入到一个线程组中去

1ThreadGroup tg = new ThreadGroup("My Group");
2MyThread2 thrd = new MyThread2(tg, "MyThread #1");
3MyThread2 thrd2 = new MyThread2(tg, "MyThread #2");
4MyThread2 thrd3 = new MyThread2(tg, "MyThread #3");

其中Thread中和ThreadGroup相关的构造函数：

1public Thread(ThreadGroup group, Runnable target) {  
2	init(group, target, "Thread-" + nextThreadNum(), 0);  
3}  
4  
5  
6public Thread(ThreadGroup group, String name) {  
7	init(group, null, name, 0);  
8}  
9  
10  
11public Thread(ThreadGroup group, Runnable target, String name) {  
12	init(group, target, name, 0);  
13}  
14  
15public Thread(ThreadGroup group, Runnable target, String name,  long stackSize) {  
16	init(group, target, name, stackSize);  
17}  

它们最终都是调用同一个函数：

1   private void init(ThreadGroup g, Runnable target, String name,  
2                     long stackSize) {  
3Thread parent = currentThread();  
4SecurityManager security = System.getSecurityManager();  
5if (g == null) {  
6        //安全检查  
7    if (security != null) {  
8    g = security.getThreadGroup();  
9    }  
10  
11       //设置线程组  
12    if (g == null) {  
13    g = parent.getThreadGroup();  
14    }  
15}  
16  
17   //检查可达性  
18g.checkAccess();  
19  
20    //是否有权限访问  
21if (security != null) {  
22    if (isCCLOverridden(getClass())) {  
23        security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);  
24    }  
25}  
26  
27    //往线程组添加线程但未启动  
28    g.addUnstarted();  
29  
30this.group = g;  
31this.daemon = parent.isDaemon();//是否守护线程  
32this.priority = parent.getPriority();//优先级  
33this.name = name.toCharArray();  
34if (security == null || isCCLOverridden(parent.getClass()))  
35    this.contextClassLoader = parent.getContextClassLoader();  
36else  
37    this.contextClassLoader = parent.contextClassLoader;  
38this.inheritedAccessControlContext = AccessController.getContext();  
39this.target = target;  
40setPriority(priority);  
41       if (parent.inheritableThreadLocals != null)  
42    this.inheritableThreadLocals =  
43    ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);  
44       this.stackSize = stackSize;  
45       tid = nextThreadID();  
46       this.me = this;  
47   }  

3、复制线程组：

1Thread thrds[] = new Thread[tg.activeCount()];
2tg.enumerate(thrds);

这里的activeCount很明显就是取得活动的线程，注意。默认情况 下，连同其子线程组也会进行复制。

4、未捕获异常处理

ThreadGroup中有一个uncaughtException()方法。当线程组中某个线程发生Unchecked exception异常时，由执行环境调用此方法进行相关处理，如果有必要，可以重新定义此方法

统一异常处理：

1public class ThreadGroupExec {
2
3    public static void main(String[] args) {
4        ThreadGroup threadGroup1 = new ThreadGroup("group1"){
5            @Override
6            public void uncaughtException(Thread t, Throwable e) {
7                System.out.println(t.getName() + ": " + e.getMessage());
8            }
9        };
10
11        // 这是匿名类写法
12        Thread thread1 =
13                // 这个线程是threadGroup1的一员
14                new Thread(threadGroup1, new Runnable() {
15                    @Override
16                    public void run() {
17                        // 抛出unchecked异常
18                        throw new RuntimeException("测试异常");
19                    }
20                });
21
22        thread1.start();
23    }
24}

查看构造函数：

1public class ThreadGroup implements Thread.UncaughtExceptionHandler {  
2    private final ThreadGroup parent;//父亲ThreadGroup  
3    String name;//ThreadGroupr 的名称  
4    int maxPriority;//线程最大优先级  
5    boolean destroyed;//是否被销毁  
6    boolean daemon;//是否守护线程  
7    boolean vmAllowSuspension;//是否可以中断  
8  
9    int nUnstartedThreads = 0;//还未启动的线程  
10    int nthreads;//ThreadGroup中线程数目  
11    Thread threads[];//ThreadGroup中的线程  
12  
13    int ngroups;//线程组数目  
14    ThreadGroup groups[];//线程组数组  

参考：

https://blog.csdn.net/evankaka/article/details/51627380

http://blog.csdn.net/edward\_qing\_lee/article/details/8767612

https://www.cnblogs.com/yiwangzhibujian/p/6212104.html