java - How to debug a multi-threaded app in IntelliJ?

Question

I'm having a strange issue with multiple threads and breakpoints in IntelliJ IDEA 14.0.2. Code after the breakpoint is executed before it stops on it.

import java.util.concurrent.atomic.AtomicInteger;


public class Main {

    private static final int NUM_CLIENTS = 1000;

    static class TestRunnable implements Runnable {
        AtomicInteger lock;
        @Override
        public void run() {
            synchronized (this.lock) {
                int curCounter = this.lock.addAndGet(1);
                System.out.println("Thread: " + Thread.currentThread().getName() + "; Count: " + curCounter);
                if (curCounter >= NUM_CLIENTS) {
                    lock.notifyAll();
                }
            }
        }
    }

    public static void main(final String args[]) {
        final AtomicInteger lock = new AtomicInteger(0);
        for (int i = 0; i < NUM_CLIENTS; i++) {
            TestRunnable tr1 = new TestRunnable();
            tr1.lock = lock;
            new Thread(tr1).start();
        }
        synchronized (lock) {
            try {
                lock.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Main woken up");
        }
    }
}

When I put a breakpoint (Suspend All) at line 12, synchronized (this.lock), System.out.println still executes (sometimes several times). Here's a screenshot:

As far as I know, all threads should stop at the breakpoint.

Answer 1

The documentation reads confusingly, but this is the relevant block. What it distills down to is setting the property to suspend on threads, and not the entire application instead. This will cause you to hit the break point on each individual thread instead of an arbitrary, indeterminate thread.

• Suspend Policy: All
  • When a breakpoint is hit, all threads are suspended.
• Suspend Policy: Thread
  • When the breakpoint is hit, the thread where the breakpoint is hit is suspended.