PA1 Discussion

Today Review Multithreading in Java Discuss Client-Server Architecture Some Hints on PA1

Thread Concepts A program may consist of many tasks that can run concurrently. A thread is the flow of execution of a task.

Thread Concepts In Java, each task is an instance of the Runnable interface, also called a runnable object. A thread is essentially an object that facilitates the execution of a task.

Thread Concepts When your program executes as an application, the Java interpreter starts a thread for main method. You can create additional threads to run concurrent tasks. Task 1: print the letter “a” 50 times Task 2: print the letter “b” 50 times Task 3: print the integers 1 through 50 Example 1: TestThread1.java

Thread Concepts Another way to create a multithreading program is to define a class that extends class Thread and implements the run() method.

Thread Concepts We will take this approach for PA1! Another way to create a multithreading program is to define a class that extends class Thread and implements the run method. Task 1: print letter “z” 50 times Task 2: print integers 1 through 50 Example 2: TestThread2.java

Thread Synchronization A shared resource may become corrupted if it is accessed simultaneously by multiple threads. To avoid race conditions, it is necessary to prevent more than one thread from simultaneously entering a certain part of the program. The keyword synchronized: acquire a lock of an object or class first before executing a block of code or a method. Example 3: TestThread3.java

Part I: Writing a Client-Server Application #status I just woke up! #statusPosted User User input: I just woke up!

Part II: Implementing a Broadcast Status Update Using Multi-threading How does the server manage multiple clients? How does each user broadcast messages?

Part III: Adding Friendship / Multicast Capability to the Social Media App private final userThread[] threads; ArrayList<String> friends = new ArrayList<String>(); ArrayList<String> friendrequests = new ArrayList<String>(); //keep track of sent friend requests