Question

I have developed a solution for Readers-Writers problem using thread.

I have one monitor class and one Reader and one Writer class.Reader and writer class extend thread.

Now I am testing the code like this:

public static void main(String[] args) {

  ReadersWriters controller = new ReadersWriters();
  Reader r0=new Reader(controller);
  Reader r1=new Reader(controller);
  Reader r2=new Reader(controller);
  Reader r3=new Reader(controller);
  Writer w0=new Writer(controller);
  Writer w1=new Writer(controller);
  Writer w2=new Writer(controller);
  Writer w3=new Writer(controller);
  r0.run();
  w0.run();
  r2.run();
  r3.run();
  r1.run();
  r3.run();
  r2.run();
  w2.run();
  r1.run();
  w1.run();
  w3.run();
 }

And the output which I am getting is this:

Reader number 0 arrives
Reader number 0 starts to read
Reader number 0 finishes reading
Writer number 0 arrives
Writer number 0 starts to write
Writer number 0 finishes writing
Reader number 2 arrives
Reader number 2 starts to read
Reader number 2 finishes reading

…and so on.
The problem here is that I am unable to test the concurrency.Because it looks like my main program is calling Reader or writer one by one,which is not the kind of testing I am trying to achieve.

Can anyone help me please.Please feel free to ask any clarification you might need.

Answer 1

It looks like you’ve implemented a Runnable, but not wrapped it in a thread. I suspect you’re calling run() on your Runnable, rather than start() on a thread. Check the tutorial section on defining/starting a thread.

You can’t reliably test multi-threaded code in unit tests and the like. It could work one time, or many times, and only fail once in a million test cases (or immediately in production). I would favour thread-safe coding techniques (e.g. writing immutable objects), static code analysis tools (e.g. PMD), and perhaps code reviews if you’re unsure.