CAB302 Software Development

Week 11 - Threads

The classes for this week are about threads, Thread objects, inheriting from the Thread class, and implementing the Runnable interface. Mostly, we are interested in you playing with the code from the lecture (available on Blackboard).

Exercise - Some Basic ThreadWork

In this exercise, we are going to take some of the code from the lectures and run it. Then we are going to get some very necessary, if slightly trivial, practice in implementing some of the examples using the interface Runnable instead of inheriting from Thread and vice versa.

Some tasks:

• Download the lecture code, compile and run all the demos shown in the class.
• Change Packer.java so that it implements Runnable rather than extends Thread. Make the necessary changes to ThreadedFillDemo so that the program creates a Thread from Packer.
• Choose another threaded example which uses Runnable and convert it to work by subclassing Thread (You can skip this if you get it by now. More important to take a subclassed version and convert it to one which runs on the interface model).
• Change some of the data and times in ScheduleTasks to see the effect of the Timer class.
• Alter the pause times on the messages in JumbledMessage to see the effect, in both the unsynchronized and synchronized versions.

Exercise - Dining Philosophers

Run the code provided in the lecture for the Dining Philosopher's problem, and see what responses appear. Try it three or four times so that you get a feel for the program, and the difficulties which emerge.

Now try to fix this source code. The fix will have to take place in Philosopher.java. There are different ways to fix this:

• Flip a coin - Use a random number generator to return a random Boolean that decides whether to pick up the first fork.
• Look before you leap - Check if the second fork is available. If not put down the first fork. Does this lead to any other possible problems?

If you are interested in pursuing this problem further, keep track of the number of times that each philosopher gets to eat. Is the sharing of the food fair; i.e. do they each get to eat about the same number of times?