Intellij Idea - Multithreading Debug - switching between threads

Question

How to switch between threads of a suspended program?

or Any tutorial on multi-threaded debugging with Intellij Idea describing basic features - suspend, resume, switch between threads.

very good tutorials/step-by-step guide available for Netbeans: e.g. https://netbeans.org/kb/docs/java/debug-multithreaded.html

Answer 1

Trick is to set breakpoint suspend policy to - Thread. View breakpoint properties (right-click on breakpoint)

Once done threads will hit breakpoint and block, now active thread can be switched to check race conditions/deadlocks.

Following code snippet for creating deadlock:

public static void main(String args[]) {
    Thread thread1 = new Thread(null, new MyThread(obj1, obj2), "Thread-1");
    Thread thread2 = new Thread(null, new MyThread(obj2, obj1), "Thread-2");
    thread1.start();
    thread2.start();
}
class MyThread implements Runnable {
    private Object obj1;
    private Object obj2;

    MyThread(Object obj1, Object obj2) {
        this.obj1 = obj1;
        this.obj2 = obj2;
    }

    @Override
    public void run() {
        System.out.println("Acquiring locks");
        synchronized (obj1){
            System.out.println("Acquired 1st lock");
            synchronized (obj2){
                System.out.println("Acquired 2nd lock");
            }
            System.out.println("Released 2nd lock");
        }
        System.out.println("Released 1st lock");
    }
}

Answer 2

Amit,

You may be interested in an alternative threads view of the call stack, enabled by clicking the 'Restore threads view' button:

A bit of documentation around that : Debug Tool Window - Threads

Also, these questions might be useful :

1. IntelliJ Thread Debug
2. IntelliJ - pause a thread while debugging