can join() be used between Peer threads

[Prahalad Deshpande]

This is one question that has baffled me. As i read through the topics on thread I came to understand that join() method to some extent can be used to sequence the order in which the threads are executing
Now I have one question:
In all the code examples provided uptill now the thread spawning another thread calls the join method on the spawned thread. By this i mean
If thread A creates thread B then A calls b.wait() where b is an object of type thread B. So as of now we have join() helping us to allow the parent wait for the child.
But what if I have two peer threads let's say C and D both spawned by the main thread; but I want thread D to execute only after thread C executes.
How do i accomplish that.
Please help me out here. I have written a sample code for the same but i dont seem to get that right. Please help me out. I can post the code if needed

Thanks in advance
Prahalad

[Adrian Engler]

- The thread that should only start after another thread has to have a reference to the thread it should join.
- If the other thread is not yet alive, a call to join will not cause the first thread to wait (NEW state has to be taken into account).

I think the following class should do what you described:

public class JoiningRunnable implements Runnable {
 
private Thread threadToJoin;

public JoiningRunnable(Thread t) {
this.threadToJoin = t;
}

public JoiningRunnable() {
this.threadToJoin = null;
}

public void run() {
synchronized (this) {
this.notify();
}
if (this.threadToJoin != null) {
synchronized(this.threadToJoin) {
try {
while (this.threadToJoin.getState() != Thread.State.TERMINATED) {
this.threadToJoin.wait();
}
}
catch (InterruptedException ie) {
// interrupted}
}
}
}
System.out.println(Thread.currentThread().getName() + " running");
}

public static void main(String[] args) {
Thread t1 = new Thread(new JoiningRunnable(), "Thread 1");
Thread t2 = new Thread (new JoiningRunnable(t1), "Thread 2");

t1.start();
t2.start();
}
 
}