[ZEPPELIN-6691] Terminate shell terminal process on WebSocket close

shell/src/main/java/org/apache/zeppelin/shell/terminal/TerminalManager.java

@@ -69,7 +69,7 @@ public TerminalService addTerminalService(TerminalSocket terminalSocket) {
   public void removeTerminalService(TerminalSocket terminalSocket) {
     Integer terminalSocketHashcode = terminalSocket.hashCode();
     if (terminalSocket2Service.containsKey(terminalSocketHashcode)) {
-      terminalSocket2Service.remove(terminalSocketHashcode);
+      terminalSocket2Service.remove(terminalSocketHashcode).close();
     } else {
       LOGGER.error("Can't find TerminalSocket: " + terminalSocketHashcode);
       LOGGER.error(terminalSocket2Service.toString());

shell/src/main/java/org/apache/zeppelin/shell/terminal/service/TerminalService.java

@@ -35,8 +35,9 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
 
-public class TerminalService {
+public class TerminalService implements AutoCloseable {
   private static final Logger LOGGER = LoggerFactory.getLogger(TerminalService.class);
 
   private String[] termCommand;
@@ -148,6 +149,39 @@ public void onTerminalResize(String columns, String rows) {
     }
   }
 
+  @Override
+  public void close() {
+    try {
+      if (outputWriter != null) {
+        outputWriter.close();
+      }
+      if (inputReader != null) {
+        inputReader.close();
+      }
+      if (errorReader != null) {
+        errorReader.close();
+      }
+    } catch (IOException e) {
+      LOGGER.error(e.getMessage(), e);
+    }
+
+    if (process != null) {
+      destroyProcess(process);
+    }
+  }
+
+  private void destroyProcess(PtyProcess process) {
+    process.destroy();
+    try {
+      if (!process.waitFor(5L, TimeUnit.SECONDS)) {
+        process.destroyForcibly();
+      }
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      process.destroyForcibly();
+    }
+  }
+
   public void onWebSocketConnect(Session webSocketSession) {
     this.webSocketSession = webSocketSession;
     webSocketSession.setMaxIdleTimeout(60 * 60 * 1000);