ThreadGroup是Java提供的一種對執行緒進行分組管理的手段，可以對所有執行緒以組為單位進行操作，如設定優先順序、守護執行緒等。

執行緒組也有父子的概念，如下圖：

執行緒組的建立

 1 public class ThreadGroupCreator {
 2 
 3     public static void main(String[] args) {
 4         //獲取當前執行緒的group
 5         ThreadGroup currentGroup = Thread.currentThread().getThreadGroup();
 6         //
 
在當前執行緒執行流中新建一個Group1
 7         ThreadGroup group1 = new ThreadGroup("Group1");
 8         //Group1的父執行緒,就是main執行緒所在Group
 9         System.out.println(group1.getParent() == currentGroup);
10         //定義Group2, 指定group1為其父執行緒
11         ThreadGroup group2 = new ThreadGroup(group1, "Group2");
12         System.out.println(group2.getParent() == group1);
 
13     }
14 }

執行緒組的基本操作

注意：後新增進執行緒組的執行緒，其優先順序不能大於執行緒組的優先順序

 1 public class ThreadGroupBasic {
 2 
 3     public static void main(String[] args) throws InterruptedException {
 4         
 5         ThreadGroup group = new ThreadGroup("group1");
 6         Thread thread = new Thread(group, () -> {
 
 7             while(true) {
 8                 try {
 9                     TimeUnit.SECONDS.sleep(1);
10                 } catch (InterruptedException e) {
11                     e.printStackTrace();
12                 }
13             }
14         }, "thread");
15         thread.setDaemon(true);
16         thread.start();
17         
18         TimeUnit.MILLISECONDS.sleep(1);
19         
20         ThreadGroup mainGroup = Thread.currentThread().getThreadGroup();
21         //遞迴獲取mainGroup中活躍執行緒的估計值
22         System.out.println("activeCount = " + mainGroup.activeCount());
23         //遞迴獲mainGroup中的活躍子group
24         System.out.println("activeGroupCount = " + mainGroup.activeGroupCount());
25         //獲取group的優先順序, 預設為10
26         System.out.println("getMaxPriority = " + mainGroup.getMaxPriority());
27         //獲取group的名字
28         System.out.println("getName = " + mainGroup.getName());
29         //獲取group的父group, 如不存在則返回null
30         System.out.println("getParent = " + mainGroup.getParent());
31         //活躍執行緒資訊全部輸出到控制檯
32         mainGroup.list();
33         System.out.println("----------------------------");
34         //判斷當前group是不是給定group的父執行緒, 如果兩者一樣,也會返回true
35         System.out.println("parentOf = " + mainGroup.parentOf(group));
36         System.out.println("parentOf = " + mainGroup.parentOf(mainGroup));
37 
38     }
39 
40 }

執行緒組的Interrupt

 1 ublic class ThreadGroupInterrupt {
 2 
 3     public static void main(String[] args) throws InterruptedException {
 4         ThreadGroup group = new ThreadGroup("TestGroup");
 5         new Thread(group, () -> {
 6             while(true) {
 7                 try {
 8                     TimeUnit.MILLISECONDS.sleep(2);
 9                 } catch (InterruptedException e) {
10                     //received interrupt signal and clear quickly
11                     System.out.println(Thread.currentThread().isInterrupted());
12                     break;
13                 }
14             }
15             System.out.println("t1 will exit");
16         }, "t1").start();
17         new Thread(group, () -> {
18             while(true) {
19                 try {
20                     TimeUnit.MILLISECONDS.sleep(2);
21                 } catch (InterruptedException e) {
22                     //received interrupt signal and clear quickly
23                     System.out.println(Thread.currentThread().isInterrupted());
24                     break;
25                 }
26             }
27             System.out.println("t2 will exit");
28         }, "t2").start();
29         //make sure all threads start
30         TimeUnit.MILLISECONDS.sleep(2);
31         
32         group.interrupt();
33     }
34 
35 }

執行緒組的destroy

 1 public class ThreadGroupDestroy {
 2 
 3     public static void main(String[] args) {
 4         ThreadGroup group = new ThreadGroup("TestGroup");
 5         ThreadGroup mainGroup = Thread.currentThread().getThreadGroup();
 6         //before destroy
 7         System.out.println("group.isDestroyed=" + group.isDestroyed());
 8         mainGroup.list();
 9         
10         group.destroy();
11         //after destroy
12         System.out.println("group.isDestroyed=" + group.isDestroyed());
13         mainGroup.list();
14     }
15 
16 }

執行緒組設定守護執行緒組

執行緒組設定為守護執行緒組，並不會影響其執行緒是否為守護執行緒，僅僅表示當它內部沒有active的執行緒的時候，會自動destroy

 1 public class ThreadGroupDaemon {
 2 
 3     public static void main(String[] args) throws InterruptedException {
 4         ThreadGroup group1 = new ThreadGroup("group1");
 5         new Thread(group1, () -> {
 6             try {
 7                 TimeUnit.SECONDS.sleep(1);
 8             } catch (InterruptedException e) {
 9                 e.printStackTrace();
10             }
11         }, "group1-thread1").start();
12         ThreadGroup group2 = new ThreadGroup("group2");
13         new Thread(group2, () -> {
14             try {
15                 TimeUnit.SECONDS.sleep(1);
16             } catch (InterruptedException e) {
17                 e.printStackTrace();
18             }
19         }, "group1-thread2").start();
20         group2.setDaemon(true);
21         
22         TimeUnit.SECONDS.sleep(3);
23         System.out.println(group1.isDestroyed());
24         System.out.println(group2.isDestroyed());
25     }
26 }