I'm having a problem making threads wait on one another. What I'm doing is just a very simple program that has two classes, one that takes "sweets" from a bag called the child and another that puts them in called the parent. Now I'm using a boolean to control when they should each wait and that works fine.
The trouble is, I can't get them to restart. The sun toutorial says that notify() and notiftAll() will wake up a method that is allready waiting but they just dont' seem to do anything
. The two classes are shown below.
class Parent extends Thread
{
// Our thread works on this
public Bag bag;
// Constructor
public Parent(Bag bag)
{
this.bag = bag;
}
// What our thread does
public synchronized void run()
{
while (true)
{
while(bag.avail)
{
try
{
System.out.println("Parent is waiting...");
wait();
}
catch (InterruptedException e)
{
}
}
bag.sweets++;
bag.in++;
bag.avail = true; //change avail to true so that the child won't have to wait
notify();
System.out.println("parent puts in: " + bag.in + " sweets is now = " + bag.sweets);
}
}
}
// The child thread
class Child extends Thread
{
// Our thread works on this
public Bag bag;
// Constructor
public Child(Bag bag)
{
this.bag = bag;
}
// What our thread does
public synchronized void run()
{
while (true)
{
while(!bag.avail)
{
try
{
System.out.println("Child is waiting...");
wait();
}
catch (InterruptedException e)
{
}
}
//System.out.println("child takes out: " + bag.out + " sweets is now = " + bag.sweets);
bag.sweets--;
bag.out++;
bag.avail = false; //change to false so the parent need not wait
notify(); //here's the problem
}
}
}
The variables are all in a seperate class called bag. I can get this to work using "busy waiting", by making the threads loop rather than wait. I'm really stuck with this one and I just need a push in the right direction. Thanks all.