Producer-ConsumerThe problemThe overall structureMethods in java.lang.ObjectThe put methodThe get methodThe Consumer classThe test classAnother Consumer classAnother test classThe EndJan 15, 2019Producer-ConsumerAn example of using ThreadsThe problemOne Thread, the producer, is “producing” information (creating objects), while another Thread, the consumer, is “consuming” (using) itWe want the consumer to use the objects in the same order as the producer creates themWe don’t want either Thread to be “loafing”—if there is work for it to do, the Thread should be doing itWe want to absolutely avoid busy loopsExample busy loop: while (!ready) { }(the other Thread will reset the ready variable)Busy loops will consume all available CPU cycles and seriously slow down everything on the computerThe overall structureimport java.util.Vector;public class CommandList { static Vector list = new Vector(); public static void put(String s) { // code on next slide } public static String get() { // code on slide after next }}Methods in java.lang.Objectvoid wait()Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.void wait(long timeout)Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. void notify()Wakes up a single thread that is waiting on this object's monitor.void notifyAll()Wakes up all threads that are waiting on this object's monitor.The put method public static void put(String s) { synchronized (list) { list.add(s); list.notify(); } }The synchronized(list) block will take the list object as soon as it becomes available, and “lock” it so no other synchronized(list) can use it until this block is completedThere is nothing special about the list object; any object can be locked for synchronizationThe get method public static String get() { if (list.size() > 0) { synchronized (list) { return (String)list.remove(0); } } else { try { synchronized (list) { list.wait(); return get(); } } catch (InterruptedException e) { return "InterruptedException"; } } }}The Consumer classpublic class Consumer extends Thread { public void run() { while (true) { String s = CommandList.get(); System.out.println("Consuming " + s); } }}The test classpublic class CommandListTester { public static void main(String[] args) { Consumer consumer = new Consumer(); consumer.start(); CommandList.put("one"); CommandList.put("two"); sleep(2000); CommandList.put("three"); CommandList.put("four"); } private static void sleep(int ms) { try { Thread.sleep(ms); } catch (InterruptedException e) { } }}Output:Consuming oneConsuming twoConsuming threeConsuming fourAnother Consumer classimport java.util.Random;public class Consumer2 extends Thread { static Random rand = new Random(); public void run() { while (true) { String s = CommandList.get(); System.out.println("Consuming " + s); try {Thread.sleep(rand.nextInt(1000)); } catch (InterruptedException e) { } } }}Another test classimport java.util.Random;public class CommandListTester2 { static Random rand = new Random(100); public static void main(String[] args) { Consumer consumer = new Consumer(); consumer.start(); String[] words = { "one", "two", "three", "four", "five", "six" }; for (int i = 0; i < words.length; i++) { CommandList.put(words[i]); try { Thread.sleep(rand.nextInt(1000)); } catch (InterruptedException e) { } } }}The
View Full Document
Unlocking...