Multithreading in Direct 3D 12

Question

Hi I am a newbie learning Direct 3D 12.

So far, I understood that Direct 3D 12 is designed for multithreading and I'm trying to make my own simple multithread demo by following the tutorial by braynzarsoft.

https://www.braynzarsoft.net/viewtutorial/q16390-03-initializing-directx-12

Environment is windows, using C++, Visual Studio.

As far as I understand, multithreading in Direct 3D 12 seems, in a nutshell, populating command lists in multiple threads.

If it is right, it seems

• 1 Swap Chain
• 1 Command Queue
• N Command Lists (N corresponds to number of threads)
• N Command Allocators (N corresponds to number of threads)
• 1 Fence

is enough for a single window program.

I wonder

Q1. When do we need multiple command queues?

Q2. Why do we need multiple fences?

Q3. When do we submit commands multiple times?

Q4. Does GetCPUDescriptorHandleForHeapStart() return value changes?

Q3 comes from here.

https://developer.nvidia.com/sites/default/files/akamai/gameworks/blog/GDC16/GDC16_gthomas_adunn_Practical_DX12.pdf

Purpose of Q4 is I thought of calling the function once and store the value for reuse, it didn't change when I debugged.

Rendering loop in my mind is (based on Game Loop pattern), for example,

1. Thread waits for fence value (eg. Main thread).
2. Begin multiple threads to populate command lists.
3. Wait all threads done with population.
4. ExecuteCommandLists.
5. Swap chain present.
6. Return to 1 in the next loop.

If I am totally misunderstanding, please help.