Java Concurrency Threading Error

Question

I have a list of 100 strings. For each string I need to perform 3 tasks. So I introduced Concurrent threads

Class A implements Runnable
{

  String str;
  A(String s)
  {
    str = s;
  }

  public static void main(String[] args)
   {
     Runnable runnable = null;

      //For Each of my strings
      for(String s:MyList)
      {
          runnable = new A(s);
          new Thread(runnable).start();
      }
  }

   @Override
   public void run() {
       task1();
       task2();
       task3();
   }
 }

This Runs into an Exception.

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded Exception in thread "Thread-0" java.lang.OutOfMemoryError: Java heap space

How do I overcome this and restrict the Thread size?

I tried Using this.

ExecutorService pool = Executors.newFixedThreadPool(10);
pool.execute(runnable);

It doesnt work.

Answer 1

"java.lang.OutOfMemoryError: Java heap space" means pretty much exactly what it says - the heap (the place you allocate new Java objects from) is out of space. Not sure what you are doing in those tasks but it must be using a lot of memory.

You can either figure out what is taking up so much memory and reduce it. Or you can - as you mention - reduce the number of concurrent operations, which would presumably use less memory. Or you can use something like:

java -Xmx1024M A

To manually specify the amount of memory made available to the JVM. But note that just increasing the memory limit without understanding why it's using so much memory is not a good idea. I would suggest looking for a bug in these taskN() calls first.