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POMaster and slave threads should shutdown using ctrl+c
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  1. POMaster and slave threads should shutdown using ctrl+c
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    copied!<p>I'm writing a program where the Main class initializes and starts a master thread. This master thread starts <code>n</code> slave threads. The program should terminate using <code>Ctrl+C</code>. Master thread must stop slave threads and finally stop itself. I've read a lot about <code>addShutdownHook</code> and here is my simplified implementation:</p> <pre><code>package dictator; import java.util.ArrayList; import java.util.List; public class Main { public static void main(String[] args) { Master m = new Master(); m.start(); } } class Master extends Thread { List&lt;Slave&gt; slaveMonitor = new ArrayList&lt;Slave&gt;(); public Master() { for (int i = 0; i &lt; 4; i++) { Slave slaveThread = new Slave(); slaveMonitor.add(slaveThread); } Thread shutDown = new Thread() { @Override public void run() { try { System.out.format("%nShutting down threads...%n"); for (Slave s : slaveMonitor) { s.interrupt(); s.join(); } interrupt() } catch (InterruptedException ex) { ex.printStackTrace(); } } }; Runtime.getRuntime().addShutdownHook(shutDown); } @Override public void run() { for (Slave s : slaveMonitor) { s.start(); } while (true) { System.out.println(getName() + " - Master"); try { Thread.sleep(1000); } catch (InterruptedException ex) { System.out.println(getName() + " interrupted."); break; } } System.out.println(getName() + " exiting."); } } class Slave extends Thread { public Slave() {} @Override public void run() { while (true) { System.out.println(getName() + " - Slave"); try { Thread.sleep(1500); } catch (InterruptedException ex) { System.out.println(getName() + " interrupted."); break; } } } } </code></pre> <p>The <code>addShutdownHook</code> catches the signal and terminates all slaves threads, but I'm not seen the master thread exiting (lines <code>System.out.println(getName() + " interrupted.");</code> and <code>System.out.println(getName() + " exiting.");</code> in master's run body.</p> <p>Here is my terminal's output:</p> <pre><code>Thread-1 - Slave Thread-2 - Slave Thread-3 - Slave Thread-0 - Master Thread-4 - Slave Thread-0 - Master ^C Shutting down threads... Thread-1 interrupted. Thread-2 interrupted. Thread-3 interrupted. Thread-4 interrupted. </code></pre> <p>Shouldn’t I see the line following lines? <em>What I'm I doing wrong?</em></p> <pre><code>Thread-0 interrupted. Thread-0 exiting. </code></pre> <h2>Changed Master Thread</h2> <pre><code>class Master extends Thread { List&lt;Slave&gt; slaveMonitor = new ArrayList&lt;&gt;(); List&lt;Thread&gt; killList = new ArrayList&lt;&gt;(); public Master() { for (int i = 0; i &lt; 4; i++) { Slave slaveThread = new Slave(); slaveMonitor.add(slaveThread); } killList.add(this); Thread shutDown = new Thread() { @Override public void run() { try { killList.addAll(slaveMonitor); Collections.reverse(killList); System.out.format("%nShutting down threads...%n"); for (Thread t : killList) { t.interrupt(); t.join(); } } catch (InterruptedException ex) { ex.printStackTrace(); System.out.println("Interrupted shutdown process"); System.exit(1); } } }; Runtime.getRuntime().addShutdownHook(shutDown); } ... </code></pre>
 

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