Producer Consumer An example of using Threads Jan 15 2019 The problem One Thread the producer is producing information creating objects while another Thread the consumer is consuming using it We want the consumer to use the objects in the same order as the producer creates them We don t want either Thread to be loafing if there is work for it to do the Thread should be doing it We want to absolutely avoid busy loops Example 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 computer The overall structure import 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 Object void wait 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 Causes the current thread to wait until another thread invokes the notify method or the notifyAll method for this object 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 completed There is nothing special about the list object any object can be locked for synchronization The 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 class public class Consumer extends Thread public void run while true String s CommandList get System out println Consuming s The test class public 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 one Consuming two Consuming three Consuming four Another Consumer class import 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 class import 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 End
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