CMSC 433, Alan Sussman, U. Maryland (via
Bill Pugh) 1
CMSC433, Spring 2002
Programming Language
Technology and Paradigms
Java Threads
Alan Sussman
February 26, 2002
CMCS 433, Spring 2002 -Alan Sussman 2
Administrivia
•Project 2 due tomorrow at 6PM
–submit as project 2
•Project 1 commentary due March 6
–submit as project 11
–finish project 1 postmortem today
•Exam 1 coming up March 7
–practice exam posted later this weeks
•Java reading posted (finally)
CMCS 433, Spring 2002 -Alan Sussman 3
Last time -Java
•Multithreading
–Runnable interface vs. extending Thread
–InterruptedException –via interrupt()
–Synchronization
•lock per object
•synchronized methods and statements
CMCS 433, Spring 2002 -Alan Sussman 4
Synchronization example
class SyncTestextends Thread {
String msg;
public SyncTest(String s) {
msg = s;
start(); }
public void run() {
synchronized (SyncTest.class) {
System.out.print(“[“ + msg);
try { Thread.sleep(1000); }
catch (InterruptedException e) {};
System.out.println(“]”); }
}
public static void main(String [] args) {
new SyncTest(“Hello”); new SyncTest(“Synchronized”);
new SyncTest(“World”); }
}
CMCS 433, Spring 2002 -Alan Sussman 5
Wait and Notify
•Must be called inside synchronized method
or block of statements
•a.wait()
–gives up lock(s) on a
–adds thread to wait set for a
–suspends thread
•a.wait(int m)
–limits suspension to m milliseconds
CMCS 433, Spring 2002 -Alan Sussman 6
Wait and Notify (cont.)
•a.notify() resumes one thread from a’s wait list
–and removes it from wait set
–no control over which thread
•a.notifyAll() resumes all threads on a’s wait list
•resumed thread(s) must reacquire lock before
continuing
•wait doesn’t give up locks on any other objects
–e.g., acquired by methods that called this one
