Myujth

I'm trying to reproduce java.lang.OutOfMemoryError: unable to create new native thread
But with -Xss VM argument.
I'm guessing that if we have a large number of threads, and every thread takes X stack space, I will have the exception if threads*X > total stack size.
But nothing happened.

my tester:

`
public static void main(String args) throws Exception

 ThreadPoolExecutor executor = new ThreadPoolExecutor(1000, 15000, 0L, TimeUnit.MILLISECONDS,
 new LinkedBlockingQueue<Runnable>());
 int i = 0;

 try
 

 Thread.sleep(100);
 for (; i <= 10; i++)
 
 Runnable t = new Runnable()
 
 List<Object> objects = new LinkedList<>();

 public void run()
 
 while (true)
 
 objects.add(new Object());
 
 
 ;

 executor.submit(t);

 
 
 catch (Throwable e)
 
 System.err.println("stop with " + i + " threads, " + e);
 System.err.println("task count " + executor.getTaskCount());
 System.out.println("get active thread count " + executor.getActiveCount());
 executor.shutdownNow();

 

`

And my VM args are

-Xms512m -Xmx512m -Xss1g

Any Idea why I'm not having the exception? and how do I repudce it?

thanks

On most OSEes, the stack is allocated lazily, ie only the pages you actually use turn into real memory. Your process is limited to 128 to 256 TB of virtual memory per process, depending on the OS you are using, so at 1 GB per thread, you need at least 128k threads. I would try a much larger stack. E.g. 256g

EDIT: Trying this myself, it looks like it ignores stack sizes of 4g and above. The largest size is -Xss4000m on windows.

Trying to reproduce this on Windows, and it appears to overload the machine before any exception is thrown.

This is what I tried. Run with -Xss4000m, it got to over 20 threads (total 80g before my windows laptop stopped working)

You might find in Linux, it will reach a ulimit before overloading the machine.

import java.util.concurrent.*;

class A 
 public static void main(String args) throws InterruptedException 
 ThreadPoolExecutor pool = new ThreadPoolExecutor(0, Integer.MAX_VALUE,
 60L, TimeUnit.SECONDS,
 new SynchronousQueue<>());
 try 
 for (int i = 0; i < 100; i++) 
 System.out.println(i);
 pool.submit(() -> 
 try 
 System.out.println(recurse() + " size " + pool.getPoolSize());
 catch (Throwable t) 
 t.printStackTrace();
 
 return null;
 );
 Thread.sleep(1000);
 
 finally 
 pool.shutdown();
 
 

 static long recurse() 
 try 
 return 1 + recurse();
 catch (Error e) 
 try 
 Thread.sleep(10000);
 catch (InterruptedException e1) 
 e1.printStackTrace();
 
 return 1;