Java中interrupt()方法詳解附帶demo

　　Thread.interrupt()的做用是通知線程應該中斷了，到底中斷仍是繼續運行，應該由被通知的線程本身處理。當對一個線程，調用 interrupt() 時，

　　1.若是線程處於被阻塞狀態（例如處於sleep, wait, join 等狀態），那麼線程將當即退出被阻塞狀態，並拋出一個InterruptedException異常。僅此而已。

　　2.若是線程處於正常活動狀態，那麼會將該線程的中斷標誌設置爲 true，僅此而已。被設置中斷標誌的線程將繼續正常運行，不受影響。

　　首先說第二條，線程正常執行，經過interrupt()方法將其中斷標誌設置爲true，在線程中使用Thread.interrupted()方法判斷當前線程是否被設置中斷標誌。

public class StopThread implements Runnable { public static void main(String[] args) { StopThread stopThread = new StopThread(); Thread thread = new Thread(stopThread); thread.start(); System.out.println("thread starting..."); try { Thread.sleep(3000); thread.interrupt(); System.out.println("interrupt thread!"); Thread.sleep(3000); thread.join(); System.out.println("main stop!"); } catch (InterruptedException e) { e.printStackTrace(); } } @Override public void run() { int i = 1; while (!Thread.interrupted()) i++; System.out.println("i=" + i); System.out.println("thread stop!"); } } 

　　輸出：

thread starting... interrupt thread! i=-937646695 thread stop! main stop!

　　這裏再說一下interrupted()，貼一下jdk1.8源碼的方法註釋，當調用這個方法會將中斷標誌重置，若是線程繼續執行，下一次調用這個方法返回爲false，除非再次調用interrupt()方法設置一次。簡單來講就是一次interrupt()只對應一次interrupted()的true狀態。

Tests whether the current thread has been interrupted. The <i>interrupted status</i> of the thread is cleared by this method. In other words, if this method were to be called twice in succession, the second call would return false 

　　接下來研究下第一條，再寫一個簡單的demo，能夠看到線程正在sleep中，調用了interrupt()方法後，直接進入catch (InterruptedException e) {}中，而後繼續執行線程後續操做。因此在catch中寫中止線程的語句，便可達到目的。

public class StopThread implements Runnable { public static void main(String[] args) { StopThread stopThread = new StopThread(); Thread thread = new Thread(stopThread); thread.start(); System.out.println("thread starting..."); try { Thread.sleep(1000); thread.interrupt(); System.out.println("interrupt thread!"); Thread.sleep(3000); thread.join(); System.out.println("main stop!"); } catch (InterruptedException e) { e.printStackTrace(); } } @Override public void run() { try { Thread.sleep(10000); } catch (InterruptedException e) { System.out.println("throw InterruptedException!"); e.printStackTrace(); } System.out.println("thread stop!"); } }

　　輸出

thread starting... interrupt thread!
throw InterruptedException! thread stop! java.lang.InterruptedException: sleep interrupted at java.lang.Thread.sleep(Native Method) at program.javaTest.threadtest.StopThread.run(StopThread.java:30) at java.lang.Thread.run(Thread.java:745) main stop!

　　那麼還有個狀況，就是調用interrupt()時線程沒有處於阻塞，而後線程開始了sleep等三種方法阻塞，這時線程一樣會跳入catch (InterruptedException e) {}中，由於中斷標誌此時爲true。

public class StopThread implements Runnable { public static void main(String[] args) { StopThread stopThread = new StopThread(); Thread thread = new Thread(stopThread); thread.start(); System.out.println("thread starting..."); try { thread.interrupt(); System.out.println("isInterrupted : " + thread.isInterrupted()); Thread.sleep(3000); thread.join(); System.out.println("main stop!"); } catch (InterruptedException e) { e.printStackTrace(); } } @Override public void run() { long l = System.currentTimeMillis(); while (System.currentTimeMillis() - l < 5000); try { Thread.sleep(3000); } catch (InterruptedException e) { System.out.println("entry catch block!"); e.printStackTrace(); } System.out.println("thread stop!"); } }

　　輸出

thread starting... isInterrupted : true
entry catch block!
java.lang.InterruptedException: sleep interrupted at java.lang.Thread.sleep(Native Method) at program.javaTest.threadtest.StopThread.run(StopThread.java:30) at java.lang.Thread.run(Thread.java:745) thread stop! main stop!

　　這個demo中多了一個thread.isInterrupted()方法，它也是用來測試線程中斷表示，不一樣的是，它是實例方法，因此返回的是實例thread的中斷標誌，這樣用來在線程外部管理線程的地方獲得線程中斷狀態；另外isInterrupted()方法不會重置中斷標誌。用這個方法時有另一個發現，當線程進入catch後，中斷標誌重置爲false！！！

P.S.interrupt()方法就講這麼多，它和信號變量一塊兒使用能夠達到很好的中斷線程目的。可是又有了新的問題，如今可以處理sleep等3個阻塞方法，若是線程阻塞在其餘方法上，好比IO中的read，該如何處理。這個以後會放在另一篇博文中詳細介紹。