Thread monitoring

When I write multi thread programs, it's always a trouble to debug whenever a thread hangs. That's because:

1. You don't see what's going on. I don't put logging when I write a library and I don't usually use raw thread.
2. The problem is gone away if I put a debug print
3. And/or it happens only once in a hundred

So, I started thinking that if I want to resolve this, it has to be a fundamental solution instead of AdHoc one.

Now, what could be a fundamental solution for this? Before forming ideas, which may not even be applicable, I need to think what's the requirements to debug hanged threads. So, things what I want to see are:

1. State of the thread If it's running, sleeping, waiting whatsoever
2. Where the location is or which procedure is being called.
3. Who the caller of the procedure is

Looking at these, it's basically thread introspection. This means, I need to know the thread, even though once a thread is created, then we just release it to dark space hoping he can manage his wellness (I feel like a parent looking at my own child leaving the house 😢). If you need to be a worrying parent, you need to let your children have a GPS to track where they are. Okay then, let Sagittarius be a good parent for his own children (threads).

The idea came up in my mind is to change the VM architecture. Currently, a VM, as we all know it's an abbreviation of Virtual Machine, is a thread. So, whenever a thread is created, then we have a new VM. Now, there must be a manager to holds / monitor the threads. I don't dare to change names, so let's the manager kernel. Then the architecture should look like this:

+------------------------------------+
|              kernel                |
+---+--------------------------------+
    | threads
  +-+-+------+---+
  |   | main | * |
  +---+------+-|-+
               |
             +-+-+-------+---+
             | * | child | * |
             +---+-------+-|-+
                           |
                         +-+-+-------+---+
                         | * | child | * |
                         +---+-------+---+

Threads should be stored in a double-linked list and each threads should have the reference of the kernel to make my life easier. With this architecture, it seems I can add extra thread to monitor other siblings from Scheme world.

I feel I'm overlooking something but probably a good starting point.