13.5. Test Your Understanding

1:	An asynchronous delegate must have a void return value. True False
2:	Given this delegate private delegate void myDelegate(string msg); myDelegate d = new myDelegate(PrintMessage); identify the role of ia, p1, p2, and p3 in this BeginInvoke call: ia = d.BeginInvoke(p1, p2, p3);
3:	What is thread local storage used for?
4:	What is the default maximum number of threads that a thread pool can hold?
5:	What two delegates are used to create a thread directly, and how do they differ?
6:	Describe a syntactically simpler way to generate the following code: Monitor.Enter(obj); { // Code to synchronize } finally { Monitor.Exit(obj); }
7:	How many times does the following code print the console message? private static s; public static void Main() { s = new Semaphore(0, 3); // Create and start five numbered threads for(int i = 1; i <= 5; i++) { Thread t = new Thread(new ThreadStart(Worker)); t.Start(); } } private static void Worker(object num) { s.WaitOne(); Console.WriteLine("Thread enters semaphore "); Thread.Sleep(100); s.Release(); } 0 1 3 5
8:	What happens when you attempt to run this code? class UseMutex { public void ThreadStart() { Mutex mutex = new Mutex(false, "MyMutex"); mutex.WaitOne(); Console.WriteLine("Worker Thread"); } static void Main() { UseMutex obj = new UseMutex(); Thread thread = new Thread( new ThreadStart(obj.ThreadStart)); Mutex mutex = new Mutex(true, "MyMutex"); thread.Start(); Thread.Sleep(1000); Console.WriteLine("Primary Thread"); mutex.ReleaseMutex(); } } It prints: Worker Thread Primary Thread It prints: Primary Thread Worker Thread The program deadlocks and there is no output.
9:	To illustrate deadlocking, Edsger Dijkstra introduced a "Dining Philosopher" metaphor that has become a classical way of introducing resource allocation and deadlocking. The metaphor (with variations) goes like this: Five philosophers, who spend their lives alternately thinking and eating, are sitting around a table. In the center of the round table is an infinite supply of food. Before each philosopher is a plate, and between each pair of plates is a single chopstick. Once a philosopher quits thinking, he or she attempts to eat. In order to eat, a philosopher must have possession of the chopstick to the left and right of the plate. Your challenge is to design a program that creates five threads—one to represent each philosopher—that continually perform the tasks of thinking and eating. The program should implement a synchronization scheme that allows each thread to periodically acquire two chopsticks so that it can eat for a fixed or random (your choice) amount of time. After eating, a philosopher should release its chopsticks and think for a while before trying to eat again. Hint: Use Monitor.Wait() to try to acquire chopsticks, and Monitor.PulseAll() to notify all threads that chopsticks are being released.