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wait notify in threads

gudii9
gudii9 asked
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Last Modified: 2012-05-11
>>A call to wait from within synchronized code causes the thread to give up its lock and go to sleep. This normally happens to allow another thread to obtain the lock and continue some processing. The wait method is meaningless without the use of notify or notifyAll which allows code that is waiting to be notified that it can wake up and continue executing. A typical example of using the wait/notify protocol to allow communication between Threads appears to involve apparently endless loops such as

//producing code
while(true){
try{
 wait();
 }catch (InterruptedException e) {}
}

//some producing action goes here
notifyAll();
As true is notorious for staying true this, code looks at first glance like it will just loop forever. The wait method however effectively means give up the lock on the object and wait until the notify or notifyAll method tells you to wake up.



I read above wait notify from link
http://www.jchq.net/certkey/0703certkey.htm

It is not clear to me in terms how they work together.

Any ideas, resources, links, sample code highly appreciated. thanks in advance.
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Java Developer
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Top Expert 2010
Commented:
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Author

Commented:
what is poling.

Author

Commented:
i have looked the links


i did not understand this program what it means by doing wait notify from both ends as here

// A correct implementation of a producer and consumer.
class Q {
int n;
boolean valueSet = false;
synchronized int get() {
if(!valueSet)
try {
wait();
} catch(InterruptedException e) {
System.out.println("InterruptedException caught");
}
System.out.println("Got: " + n);
valueSet = false;
notify();
return n;
}
synchronized void put(int n) {
if(valueSet)
try {
wait();
} catch(InterruptedException e) {
System.out.println("InterruptedException caught");
}
this.n = n;
valueSet = true;
System.out.println("Put: " + n);
notify();
}
}

class Producer implements Runnable {
Q q;
Producer(Q q) {
this.q = q;
new Thread(this, "Producer").start();
}
public void run() {
int i = 0;
while(true) {
q.put(i++);
}
}
}

class Consumer implements Runnable {
Q q;
Consumer(Q q) {
this.q = q;
new Thread(this, "Consumer").start();
}
public void run() {
while(true) {
q.get();
}
}
}

public class PCFixed {
public static void main(String args[]) {
Q q = new Q();
new Producer(q);
new Consumer(q);
System.out.println("Press Control-C to stop.");
}
}

please advise
Mick BarryJava Developer
CERTIFIED EXPERT
Top Expert 2010

Commented:
its waits() for a value to be set
And another thread notify()s when it has been set

Author

Commented:
>>>its waits() for a value to be set
And another thread notify()s when it has been set

where in the code it is waiting for a value to set and notify when which value is set...

in this code


class Q {
int n;
boolean valueSet = false;
synchronized int get() {
if(!valueSet)
try {
wait();
} catch(InterruptedException e) {
System.out.println("InterruptedException caught");
}
System.out.println("Got: " + n);
valueSet = false;
notify();
return n;
}
synchronized void put(int n) {
if(valueSet)
try {
wait();
} catch(InterruptedException e) {
System.out.println("InterruptedException caught");
}
this.n = n;
valueSet = true;
System.out.println("Put: " + n);
notify();
}
}

class Producer implements Runnable {
Q q;
Producer(Q q) {
this.q = q;
new Thread(this, "Producer").start();
}
public void run() {
int i = 0;
while(true) {
q.put(i++);
}
}
}

class Consumer implements Runnable {
Q q;
Consumer(Q q) {
this.q = q;
new Thread(this, "Consumer").start();
}
public void run() {
while(true) {
q.get();
}
}
}

public class PCFixed {
public static void main(String args[]) {
Q q = new Q();
new Producer(q);
new Consumer(q);
System.out.println("Press Control-C to stop.");
}
}



please advise
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