wait() and notify() throw exception even if i have the lock

[cozsmin]

hello , as u know wait() and notify() will not thow an exception if the method that calls them has the lock , or esle i misundrestood java :P





this is the code that throws (unwanted) exceptions :
(or u can download it from :
http://www.geocities.com/mndt_0/file...ForThread.java
at this link it has the spaces )

public class WaitingForThread {
 
    public static void main (String []args) {
 
        String []message = {"msg 1","msg 2","msg 3"
            ,"msg 4","msg 5","msg 6","msg 7","msg 8","msg 9","msg 10"};
 
        boolean begin[] = new boolean [10];
 
        Client client = new Client(begin);
 
        Producer producer = new Producer(message,client,begin);
 
        new Thread(client).start();
 
        new Thread(producer).start();
    }
}
 
class Producer implements Runnable {
 
    String message[] = new String [10];
 
    int msgNumber;
 
    Client client;
 
    boolean begin[];
 
    Producer (String [] message, Client client,boolean [] begin) {
 
        this.message = message;
 
        this.client = client;
 
        this.begin = begin;
    }
 
    public void run() {
 
        synchronized (this.client) {
 
            while (msgNumber <message.length) {
 
                try {
 
                    Thread.sleep(200);
                }
                    catch(Exception e) {e.printStackTrace();}
 
                client.message[msgNumber] = message[msgNumber];
 
                System.out.print("\n\n Producer passed message nr "
 
                +msgNumber);
 
                begin[msgNumber] = true;
 
 
                try {
 
                    notify();
                    System.out.print("\n\n the producer waits now..");
                    wait();
                }
 
                catch (Exception e) {e.printStackTrace();}
 
                msgNumber++;
            }
 
 
    /*        while(true) {
 
                try {
 
                    Thread.sleep(200);
                    System.out.print("\n\n producer `s run()");
                }            
                    catch (Exception e) {};
            }
 
    */
 
        }
    }
} 
 
class Client implements Runnable{
 
    int msgNumber;
 
    boolean begin[];
 
    String [] message = new String[10];
 
    Client(boolean []begin) {
 
        this.begin = begin;
    }
 
    synchronized public void run () {
 
        while (true) {
 
            while (!begin[msgNumber]) {
 
                try {
                        System.out.print("\n\n the client is waiting for the Producer\n\n");
        //                System.out.print("\n\n begin["+msgNumber+"] = "+begin[msgNumber]);
                        Thread.sleep(3000);
                        notify();
                        wait();
                    }
 
                    catch (Exception e) {e.printStackTrace();}
            }
 
            if (message[msgNumber]!=null) {
 
                System.out.print("\n\n client is thinking..");
 
                try {
 
                    Thread.sleep(2000);
                }
 
                catch(Exception e) {e.printStackTrace() ;}
 
                System.out.print("\n\n client says : \""+message[msgNumber++]
                +"\"\n\n");
 
                try {
 
                    notify();                    
                    System.out.print("\n\n client is waiting..");
                    wait();
                }
 
                catch (Exception e) {e.printStackTrace();}
            }
 
 
 
    /*        while(true) {
 
                try {
 
                    Thread.sleep(200);
                    System.out.print("\n\n clinet `s run ()");
                }            
                    catch (Exception e) {};
            }
 
    */
 
        }
    }
}
 

i put the /* */ to see if the 2 run() were synchronidez and they were, too se , just put /* */ the rest of the run()1s body for each class , and u will see that only one run() will print.

[JosAH]

Which Exception has been thrown? Can you produce a stack trace?

kind regards,

Jos

[cozsmin]

java.lang.Illeg alMonitorStateE xception

at java.lang.Objec t.notify(Native Method)
at Producer.run(Wa itingForThread. java 63) // it wa 64 but i took out the package
at java.lang.Threa d.run(Unkown Source)


it has the stackTrace built in th script ;
just run the code and see

[JosAH]

I found it: in Java you always synchronize, wait and notify on a certain object.
Your code waits on the client object (that's why you pass the client to the
Producer's constructor).

In your Producer you don't wait/notify on the client, i.e. you simply do this:

wait();
notify();

instead of:

client.wait();
client.notify();

kind regards,

Jos

[cozsmin]

that is it, instead of .wait() or .notify() on the object i was locked on ( producer is syncronized on client) , i did this.notify() and this.wait()

[JosAH]

that is it, instead of .wait() or .notify() on the object i was locked on ( producer is syncronized on client) , i did this.notify() and this.wait()

Yep, that's it; problem solved ;-)

kind regards,

Jos