CM10228 Concurrency

In the early days of computing when programs were written on punch cards, you had to book a time slot on the computer in order to get to run your program. Errors, having to wait for input, or even just someone booking too much time were hugely inefficient uses of computing power when there were other programs that needed to be run. Nowadays, operating systems are ubiquitous, and it is possible to run multiple programs at the same time with no obvious switching, as far as the user is concerned. This area of computer science is called concurrency. A thread is like a 'worker' that runs some instructions. Using multiple threads allows the processor to allocate time to different programs and switch between them seamlessly. Furthermore, if one program is busy waiting for something that the processor can't help (e.g. user input), then it can spend time on the others instead. But that's not all, a single program will often have multiple threads. The primary purpose of this is so that it can handle multiple jobs 'at the same time'. For instance, a game might have one thread running the GUI, another running the AI, and another communicating over the network. Since multi-processor and multi-core systems came along, threads are also useful for separating a single large task to be handled more efficiently by separate processors (or cores).

Do this:

Open the Oracle Java Tutorial on concurrency.

Question:

Can you explain the two different ways of writing a Thread in Java? What are their benefits and which is more useful? (The first four pages of the tutorial should help you here.)

Task:

Implement this in Java:

Write a thread which just prints the numbers from 1 to 100, prefaced with "Thread: " and then dies. i.e. "Thread: 1", "Thread: 2", etc.

Create a class with a main method, which creates and runs your thread. It then goes on to print the numbers from 1 to 100, prefaced with "Main: ", i.e. "Main 1", "Main 2".

You should see that your thread and your main method take it in turns to print their numbers. But notice that it is not perfect, you cannot rely on them getting the same amount of time to perform their actions. Only that they will be roughly happening at the same time.
You have made a thread! It really is that easy. Just this will be enough to get you far with threading. But you should continue to read and learn about some other features before we move on.

Try adding calls to the method sleep(...) to the program you made in the previous step. (The next page of the tutorial should help.)

Try implementing the code that you find on each page up to and including The SimpleThreads Example, either by adding it to your previous program, a new one, or just download the code from the website. Experiment, it is the best way to learn.

Now you have learned the basics of threads. This is all you need for this sheet, however there are a few more topics that are worth learning and will help you with coursework 2, in particular:

CM10228 / Programming Ib: Lab 2

Concurrency and Networking: Threading (Concurrency)

Background:

Do this:

Do this: (in your own time)