Producer Consumer (Semaphore?)
I am trying to understand concurrency in Java and have tried to code a producer consumer example:
package de.fasel;
publicclass PackagingUnit{
privateint numberOfUnits;
privatestaticfinalint PACKAGE_SIZE = 50;
public PackagingUnit(){
this.numberOfUnits = 0;
}
publicvoid addUnit(){
numberOfUnits++;
notify();
}
publicvoid getPackage(){
while (this.numberOfUnits < 50)
try{
wait();
}catch (InterruptedException e){
// TODO Auto-generated catch block
e.printStackTrace();
}
this.numberOfUnits -= PACKAGE_SIZE;
}
}
package de.fasel;
import java.util.concurrent.TimeUnit;
publicclass Producerimplements Runnable{
privateint productionTime;
private PackagingUnit pUnit;
private String name;
/**
* @param productionTime in sec int
* @param pUnit
* @param name
*/
public Producer(int productionTime, PackagingUnit pUnit, String name){
this.productionTime = productionTime;
this.pUnit = pUnit;
this.name = name;
}
publicvoid run(){
while (true){
try{
TimeUnit.SECONDS.sleep(productionTime);
}catch (InterruptedException e){
// TODO Auto-generated catch block
e.printStackTrace();
}
this.pUnit.addUnit();
System.out.printf("%s has produced one unit", name);
}
}
}
package de.fasel;
publicclass Shipperimplements Runnable{
private PackagingUnit pUnit;
public Shipper(PackagingUnit unit){
super();
// TODO Auto-generated constructor stub
pUnit = unit;
}
publicvoid run(){
while(true){
this.pUnit.getPackage();
System.out.println("One package has been shipped");
}
}
}
package de.fasel;
publicclass Tester{
publicstaticvoid main(String[] args){
PackagingUnit pUnit =new PackagingUnit();
Producer p1 =new Producer(3, pUnit,"p1");
Producer p2 =new Producer(2, pUnit,"p2");
Producer p3 =new Producer(1, pUnit,"p3");
Producer p4 =new Producer(1, pUnit,"p4");
Shipper s =new Shipper(pUnit);
Thread tp1 =new Thread(p1);
tp1.start();
Thread tp2 =new Thread(p2);
tp2.start();
Thread tp3 =new Thread(p3);
tp3.start();
Thread tp4 =new Thread(p4);
tp4.start();
Thread ts =new Thread(s);
ts.start();
}
}
When I run this I get the following exception
Exception in thread "Thread-4" java.lang.IllegalMonitorStateException: current thread not owner
at java.lang.Object.wait(Native Method)
at java.lang.Object.wait(Unknown Source)
at de.fasel.PackagingUnit.getPackage(PackagingUnit.java:20)
at de.fasel.Shipper.run(Shipper.java:15)
at java.lang.Thread.run(Unknown Source)
How can I make this work?
Thanks
