How to run different methods parallely

Question

I have one java method which contains 5 different internal methods. For performance improvement, I want to call these methods parallely.

e.g. run method1, method2, ... method5 parallel using thread.

private void getInformation() throws SQLException,
            ClassNotFoundException, NamingException {
    method1();
    method2();
    method3();
    method4();
    method5();
}

but all these 5 methods have different business logic.

Answer 1

Do something like this:

1. For each method, create a Callable object that wraps that method.
2. Create an Executor (a fixed thread pool executor should be fine).
3. Put all your Callables in a list and invoke them with the Executor.

Here's a simple example:

public void testThread()
{

   //create a callable for each method
   Callable<Void> callable1 = new Callable<Void>()
   {
      @Override
      public Void call() throws Exception
      {
         method1();
         return null;
      }
   };

   Callable<Void> callable2 = new Callable<Void>()
   {
      @Override
      public Void call() throws Exception
      {
         method2();
         return null;
      }
   };

   Callable<Void> callable3 = new Callable<Void>()
   {
      @Override
      public Void call() throws Exception
      {
         method3();
         return null;
      }
   };

   //add to a list
   List<Callable<Void>> taskList = new ArrayList<Callable<Void>>();
   taskList.add(callable1);
   taskList.add(callable2);
   taskList.add(callable3);

   //create a pool executor with 3 threads
   ExecutorService executor = Executors.newFixedThreadPool(3);

   try
   {
      //start the threads and wait for them to finish
      executor.invokeAll(taskList);
   }
   catch (InterruptedException ie)
   {
      //do something if you care about interruption;
   }

}

private void method1()
{
   System.out.println("method1");
}

private void method2()
{
   System.out.println("method2");
}

private void method3()
{
   System.out.println("method3");
}

Make sure each method does not share state (like a common mutable field in the same class) or you may get unexpected results. Oracle provides a good introduction to Java Executors. Also, this book is awesome if you are doing any kind of threading in java.