parallele-programmierung/u07-3

Problem 7.3: Compare different Executor implementations

a)

Two important parameters of class ThreadPoolExecutor are corePoolSize and maximumPoolSize. Read about their effect, e.g. at https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/util/concurrent/ThreadPoolExecutor.html or in Java Concurreny in Practice, chapter 8. Write an algorithm in pseudo code that describes what happens when a new task is submitted and another algorithm describing what happens when a task is finished. These two algorithms must use the corePoolSize the maximumPoolSize and the keepAliveTime.

Answer:

function execute(runnable) {
	if (runningThreads.size() < corePoolSize) {
		createNewThread();
	} else if (runningThreads.size() < maximumPoolSize && queue.isFull()) {
		createNewThread();
	}
}

function onTaskCompletion() {
	if (runningThreads > corePoolSize) {
		for (thread : runningThreads) {
			if (thread.idleTime() > keepAliveTime) {
				thread.terminate();
			}
		}
	}
}

b)

Now consider the thread pools created by the factory methods newFixedThreadPool(int nThreads) and newCachedThreadPool() mentioned on slide 5-19 (you can find further details at https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/util/concurrent/Executors.html): How can you create these two kinds of thread pool using the general constructor ThreadPoolExecutor()?

Answer:

ThreadPoolExecutor fixedThreadPool = new ThreadPoolExecutor(n, n);
ThreadPoolExecutor cachedThreadPool = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS);