Object sychronized and thread notifyAll

find out a snip of multi-thread testing code.  when try to run it on NetBeans, encounter an error

IllegalMonitorStateException: current thread not owner

 

After investigation, find out the root cause is:

can't do a notifyAll without having a lock on the object first.

 

 

So record it as a knowledge capture.

 

 

code as following:

Main.java

package forumtest;public class Main { /** * @param args the command line arguments */ public static void main(String[] args) { Forum forum = new Forum(2); for(int i = 0; i < 50; i ++) { Member mem = new Member("memeber "+ i, forum); } }}

Forum.java

package forumtest;public class Forum { private int emptysite; private static int numberorder=0; public Forum( int es){ emptysite = es; }public synchronized void joinin(){ if(emptysite == 0 ){ try{ wait(); }catch(InterruptedException ie){ ie.printStackTrace(); } } emptysite --; numberorder ++; System.out.println("join in " + numberorder);}public synchronized void leave(){ emptysite ++; notifyAll(); System.out.println("leave one member");}}

 

Member.java

package forumtest;public class Member extends Thread{ private Forum forum; private String name; public Member(String name, Forum forum){ super(name); this.forum = forum; this.start(); } public void run() { try{ sleep((int)(Math.random()*10000)); }catch(InterruptedException ie){ ie.printStackTrace(); } forum.joinin(); try{ sleep((int)(Math.random()*10000)); }catch(InterruptedException ie){ ie.printStackTrace(); } forum.leave(); try{ sleep((int)(Math.random()*10000)); }catch(InterruptedException ie){ ie.printStackTrace(); } }}