How to restrict the multithreading in a Java program?

Question

I am creating an online judge, for this I want that the submitted java code should not utilize the parallel processing of CPU. So, I want that the multi threading of the Java application to be disabled.

The application sent to the server would be just a single java file, it would be compiled to byte code and then executed, suppose the application is using threads, it is creating a thread, the application should be closed by throwing some exception like Permission Denied like error.

Possible duplicate of [Thread creation listener](https://stackoverflow.com/questions/12491112/thread-creation-listener) — Tibrogargan, Jun 07 '19 at 06:54
I would be not using, some user who is using my online judge can, he may send the code which includes the threads, so I want to reject his code by throwing some exception or by introducing some error — Nimit Bhardwaj, Jun 07 '19 at 06:54
You have to use a security manager: https://stackoverflow.com/a/31039987/2588800 — Svetlin Zarev, Jun 07 '19 at 06:56
@Tibrogargan it involves in the code, I would be executing the code simply by `java ,` so I would not be adding wrapper — Nimit Bhardwaj, Jun 07 '19 at 06:56
@Tibrogargan I think this too, I think have to invoke the class by a java application — Nimit Bhardwaj, Jun 07 '19 at 07:00
@SvetlinZarev, You should re-post that comment as an answer. And Nimit, You should accept the answer if Svetlin re-posts it and it works for you. — Solomon Slow, Jun 07 '19 at 14:47
You can do bytecode manipulation at runtime (possible with [ByteBuddy](https://bytebuddy.net/)) and create proxy classes to stop user from creating a native thread and throwing some exception/error. — Lavish Kothari, Jun 08 '19 at 05:45

score 0 · Answer 1 · answered Jun 07 '19 at 16:04

0

Instead of threads, use a tread pool. Create a threadpool with desired parallelism, for example, 1:

ExecutorService threadPool = Executors.newFixedThreadPool(1);

replace thread creation with submitting tasks to the thread pool:

Runnable r = ...
Thread t = new Thread(r);
t.start();
...
t.join();

replace with

Runnable r = ...
Future<Void> future = executorService.submit(r);
...
future.get();

this way you can create as many parallel tasks as you want.

answered Jun 07 '19 at 16:04

Alexei Kaigorodov

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This answer does not help the OP because the OP is not the author of the code that might create threads. The OP wants to create a system to _judge_ the code (e.g., think "coding contest.") The contest rules say, "single threaded," and the OP wants an automated way to reject entries that don't obey that rule. – Solomon Slow Jun 10 '19 at 18:09
Yes, Its not what I wanted, I want to enforce the multithreading to only 1. I was trying to use apparmor for it, still no progress – Nimit Bhardwaj Jun 11 '19 at 06:40

How to restrict the multithreading in a Java program?

1 Answers1