Develop Reference

How to handle third-party Java code in a Task submitted to ExecutorService in case it has an infinite loop

Let's say I have a third-party Java library called in a Task submitted to ExecutorService.
I trust the third-party library to not be malicious, but there is a rare chance that there are programming errors that can cause it to get stuck in an infinite loop, and if this is the case, I cannot fix it to address those rare occasions.
What is the best way to handle this so that the application doesn't get stuck as well? Is shutdownNow() good enough to handle this situation?
There's a related issue Stop an infinite loop in an ExecutorService task but this relies on the ability of the programmer to be cooperative and detect Thread.currentThread().isInterrupted() to stop processing, which I can't rely on.
(In my case it's Jython code; in an early version of Jython the interpreter apparently didn't check Thread.currentThread().isInterrupted(), not sure what it does now... but my question is general for any 3rd-party Java code.)

If the task has an infinite loop that does not check for the thread interrupted status and does not use methods that throw InterruptedExceptions, it won't be stopped by shutdownNow().
Simple example that doesn't allow you program to finish:
public static void main(String[] args) throws Exception {
ExecutorService e = Executors.newFixedThreadPool(1);
e.submit(() -> { while (true); });
e.shutdownNow();
System.out.println("Main is finished but the app keeps running");
}
One way would be to run the thread as a daemon:
public static void main(String[] args) throws Exception {
ExecutorService e = Executors.newFixedThreadPool(1, r -> {
Thread t = new Thread(r);
t.setDaemon(true);
return t;
});
e.submit(() -> { while (true); });
e.shutdownNow();
System.out.println("Main is finished and the app can exit");
}

Following my correct reading of the question I put together this set of classes. Relatively simple: One Runnable that connects to a socket sending input and retrieving output from a secondary jvm that invokes the erratic library.
If after 3 tries no response has been received the secondary jvm is killed. But it could be relaunched. The secondary jvm has an exit hook to close down sockets.
class SafetyValve implements Runnable{
PrintWriter out;
BufferedReader in;
Socket s = null;
AtomicBoolean flag;
SafetyValve(AtomicBoolean b){
flag = b;
}
#Override
public void run() {
try {
s = new Socket("localhost", 9000);
out = new PrintWriter(s.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(s.getInputStream()));
while (!Thread.currentThread().isInterrupted()){
flag.set(false);
out.print(0);
out.flush();
System.out.print(in.read());
flag.set(true);
}
} catch (Exception e) {
e.printStackTrace();
}
finally{
try {
s.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
Main/Controller class. It uses a Thread class for control
public class Switch {
public static void main(String[] args) {
try {
AtomicBoolean flag = new AtomicBoolean(false);
int counter = 0;
ProcessBuilder pb = ...
pb.directory(,,,);
Process p = pb.start();
SafetyValve sv = new SafetyValve(flag);
Thread t = new Thread(sv);
t.start();
while(t.getState() != Thread.State.RUNNABLE){
Thread.sleep(10);
}
while(true){
if (flag.get() == false){
if (++counter == 3){
while(t.getState() != Thread.State.TERMINATED){
p.destroyForcibly();
t.interrupt();
Thread.sleep(10);
}
break;
}
}
else
counter = 0;
Thread.sleep(100);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
The secondary jvm has an standard server socket implementation:
class UnYielding{
int i = 0;
int returnInt(){
i++;
if (i > 2)
while(true);
return i;
}
}
class Hook extends Thread{
RunWild rw;
Hook(RunWild wr){
rw = wr;
}
public void run() {
try {
System.out.println("exit...");
System.out.flush();
rw.socket.close();
rw.server.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public class RunWild {
ServerSocket server;
Socket socket;
RunWild(){
Runtime.getRuntime().addShutdownHook(new Hook(this));
}
public static void main(String[] args){
UnYielding u;
int i;
PrintWriter out;
BufferedReader in;
RunWild rw = new RunWild();
try {
rw.server = new ServerSocket(9000);
rw.socket = rw.server.accept();
out = new PrintWriter(rw.socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(rw.socket.getInputStream()));
u = new UnYielding();
while ((i = in.read()) != -1){
out.print(u.returnInt());
out.flush();
Thread.sleep(10);
System.out.print("waiting...");
System.out.flush();
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
I have tested this against 1.8 on OS X it works as expected. If this unstable classes are needed this is one way of doing it

Java File.deleteOnExit() not working Windows 10

I'm trying to write code for a jarfile which if executed, it shutdowns the JVM and then deletes the jarfile. This is what I've tried to do so far but it is not deleting the file after the JVM closes.
public static void check() {
if (isJarFile()) {
try (Scanner s = new Scanner(new URL(HASH_PROVIDER).openStream())) {
String remote_hash = s.nextLine().trim();
File jarFile = getJarFile();
if (jarFile != null && !remote_hash.equals(getMD5Checksum(jarFile.getAbsolutePath()))) {
jarFile.setWritable(true);
jarFile.deleteOnExit();
}
System.exit(0);
} catch (Exception e) {
e.printStackTrace();
System.exit(0);
}
}
}
public static byte[] createChecksum(String filename) throws Exception {
InputStream fis = new FileInputStream(filename);
byte[] buffer = new byte[1024];
MessageDigest complete = MessageDigest.getInstance("MD5");
int numRead;
do {
numRead = fis.read(buffer);
if (numRead > 0) {
complete.update(buffer, 0, numRead);
}
} while (numRead != -1);
fis.close();
return complete.digest();
}
public static String getMD5Checksum(String filename) throws Exception {
byte[] b = createChecksum(filename);
String result = "";
for (int i = 0; i < b.length; i++) {
result += Integer.toString((b[i] & 0xff) + 0x100, 16).substring(1);
}
return result;
}
public static File getJarFile() {
try {
return new File(Main.class.getProtectionDomain().getCodeSource().getLocation().toURI().getPath());
} catch (URISyntaxException e) {
e.printStackTrace();
}
return null;
}
Can someone explain why deleteOnExit is not working in this instance?

Make sure that you close any stream that you have open on a file before exiting your JVM. Otherwise, the shut down hook that is supposed to delete the file cannot trigger on Windows as opening the stream triggers a file lock on the OS-level.
For your example, it means that you must not end the JVM process before exiting the try-with-ressources-block which is roughly translated into:
Scanner s = new Scanner(new URL(HASH_PROVIDER).openStream())
try {
// your code
System.exit(0);
} finally {
s.close(); // Never executed
}
As your program exits before the finally block is executed, the shut down hook is triggered without closing the stream and the file cannot be deleted.
Note that the following code will work for your purposes as the finally block is executed after closing the try-with-ressources argument:
try (Scanner s = new Scanner(new URL(HASH_PROVIDER).openStream())) {
// your code
} catch (Exception e) {
e.printStackTrace();
} finally {
System.exit(0);
}

cmd command from java application error

Recently I added "adb devices" in the nano ./bash_profile so that I can run it from any directory.
I used one java application to run
public static void main(String [] args) {
executeCmd("adb devices");
}
private static void executeCmd(String string) {
InputStream pipedOut = null;
try {
Process aProcess = Runtime.getRuntime().exec(string);
// These two thread shall stop by themself when the process end
Thread pipeThread = new Thread(new StreamGobber(aProcess.getInputStream()));
Thread errorThread = new Thread(new StreamGobber(aProcess.getErrorStream()));
pipeThread.start();
errorThread.start();
aProcess.waitFor();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
class StreamGobber implements Runnable {
private InputStream Pipe;
public StreamGobber(InputStream pipe) {
if(pipe == null) {
throw new NullPointerException("bad pipe");
}
Pipe = pipe;
}
public void run() {
try {
byte buffer[] = new byte[2048];
int read = Pipe.read(buffer);
while(read >= 0) {
System.out.write(buffer, 0, read);
read = Pipe.read(buffer);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if(Pipe != null) {
try {
Pipe.close();
} catch (IOException e) {
}
}
}
when I run any other commands such as "ls" it's working fine!!
I'm using mac ..
thanks :)

Maybe global path problem on mac. You can try run with absolute adb program path as command.

Java NIO Pipe and ByteBuffer

I'm trying to pipe some ByteBuffer in a thread (IO1) to another (IO2).
http://tutorials.jenkov.com/java-nio/pipe.html
private int bufferSize;
private boolean isRecording;
private Thread IO1;
private Thread IO2;
private ByteBuffer byteBuffer1;
private ByteBuffer byteBuffer2;
private Pipe pipe;
private Pipe.SinkChannel skChannel;
private Pipe.SourceChannel sourceChannel;
byteBuffer1 = ByteBuffer.allocateDirect(bufferSize);
byteBuffer2 = ByteBuffer.allocateDirect(bufferSize);
//An instance of Pipe is created
try
{
pipe = Pipe.open();
skChannel = pipe.sink();
sourceChannel = pipe.source();
IO1.start();
IO2.start();
}
catch (IOException e)
{
e.printStackTrace();
}
--
IO1 = new Thread(new Runnable()
{
public void run()
{
isRecording = true;
recorder.startRecording();
try
{
int read;
while (isRecording)
{
// byteBuffer1.clear();
read = recorder.read(byteBuffer1, bufferSize);
if (AudioRecord.ERROR_INVALID_OPERATION != read)
{
skChannel.write(byteBuffer1);
Log.v("========IO1 ", String.valueOf(read));
//This triggered almost 20 times/second
}
}
recorder.stop();
}
catch (Exception e)
{
e.printStackTrace();
}
}
});
skChannel.write(byteBuffer1); and
Log.v("========IO1 ", String.valueOf(read));
is triggered almost 20 times/second, and this is the expected behavior, so far so good.
IO2 = new Thread(new Runnable()
{
public void run()
{
try
{
int read;
while ( (read =sourceChannel.read(byteBuffer2)) >0)
{
Log.v("========IO2 ", String.valueOf(read));
//this triggered only once
// To do Codec etc.
//............
}
}
catch (IOException e)
{
e.printStackTrace();
}
Log.v("========IO2 ", "END!!!!!"); //never triggered(this is fine)
}
});
However, Log.v("========IO2 ", String.valueOf(read)); is triggered only once, and I don't know why.
Can someone tell me how can I obtain the update of Thread IO1 in IO2?
Thanks.

You need to flip() the buffer before writing, and compact() it afterwards.
BUT: In a word, don't. Pipes between threads are basically pointless. Use a queue, or have the receiving thread read the sending thread's input directly.
If you must do this, the basic NIO copy loop goes like this:
while (in.read(buffer) > 0 || buffer.position() > 0) // or whatever your read API needs
{
buffer.flip();
out.write(buffer);
buffer.compact();
}

Blackberry Best way to retry connection if failed?

I have the following code, i want to be able to restart the thread if an exception occurred while processing a request.
The following in the run method of a thread:
int status = httpConn.getResponseCode();
if (status == HttpConnection.HTTP_OK) {
// Is this html?
String contentType = httpConn
.getHeaderField(HEADER_CONTENTTYPE);
boolean htmlContent = (contentType != null && contentType
.startsWith(CONTENTTYPE_TEXTHTML));
InputStream input = s.openInputStream();
byte[] data = new byte[1000];
int len = 0;
int size = 0;
StringBuffer raw = new StringBuffer();
while (-1 != (len = input.read(data))) {
// Exit condition for the thread. An
// IOException
// is
// thrown because of the call to
// httpConn.close(),
// causing the thread to terminate.
if (_stop) {
httpConn.close();
s.close();
input.close();
}
raw.append(new String(data, 0, len));
size += len;
}
// raw.insert(0, "bytes received]\n");
// raw.insert(0, size);
// raw.insert(0, '[');
content = raw.toString();
if (htmlContent) {
content = prepareData(raw.toString());
}
input.close();
} else {
try{
httpConn.close();
}catch (Exception e) {
// TODO: handle exception
}
errorDialog(status+", status code");
retryFeed(getUrl(), "Network error. Retrying...");
}
s.close();
} else {
errorDialog("Sorry Insufficient Network Coverage.");
return;
}
} catch (IOCancelledException e) {
errorDialog(e.getMessage());
retryFeed(getUrl(), "Network error. Retrying...");
} catch (IOException e) {
errorDialog(e.getMessage());
retryFeed(getUrl(), "Network error. Retrying...");
}
What is the safest way to retry the connection if failed?
Thanks.
//New This is the Error thread. That check for errors in the connection... will this help? and is it the most efficient method? thanks..
/Error Thread - Thread to check errors/
private class ErrorThread extends Thread {
private static final int TIMEOUT = 3000; // EVERY 3 Seconds
private boolean hasException = false;
private String _theUrl;
/**
* Stops this thread from listening for messages
*/
private synchronized void stop()
{
hasException =false;
}
/**
* Listens for incoming messages until stop() is called
* #see #stop()
* #see java.lang.Runnable#run()
*/
public void run()
{
try
{
while (true) {
if((hasException==true))
{
// Synchronize here so that we don't end up creating a connection that is never closed.
errorDialog("Will Fetch new");
synchronized(this)
{
hasException=false;
if (!_connectionThread.isStarted()) {
fetchPage(_theUrl);
} else {
createNewFetch(_theUrl);
}
}
}
try {
//errorDialog("No exception.");
sleep(TIMEOUT);
} catch (InterruptedException e)
{
errorDialog("Exceptions"+e.toString()+e.getMessage());
System.exit(1);
//System.exit(0);/*Kill System*/
}
}
}
catch (Exception except)
{
}
}
public void setActive(boolean exception,String url)
{
this.hasException=exception;
this._theUrl=url;
}
}

If the connecrtion fails, typically, you want to close it, pause a small time, and retry. The purpose of the pause is to prevent your device from devoting excessive resources to trying to connect to a server that's having issues.