libcommon VS assembly

If you like Lua coroutines and C++20 coroutines, I have written a piece of code that allows to combine both: https://github.com/CM4all/libcommon/blob/master/src/lua/CoAw...

It's used for example by our "myproxy" project: https://github.com/CM4all/myproxy/blob/master/src/Connection... (Ctrl-F Lua::CoAwaitable) - a Lua coroutine is launched from within a C++20 coroutine and the C++20 coroutine awaits the Lua coroutine. Everything integrated in a non-blocking I/O event loop.

When you're learning something for the first time, it can be hard to know what mental model you need to have to be effective with the tool.

Some documentation is reference material. With reference material you might navigate the reference material in a particular traversal to get what you need to do what you want.

But at the beginning of your journey, you need to be taught a "flow" an expected pattern of operation to build up the right mental model of how an average session with the tool works. For programming this might be the edit file, compile, run, debug loop, or TDD or IntelliJ's build and deploy. Or a CI system commit, push, deploy, promote cycle. Or kubernetes kubectl edit, apply.

I opened the "dining philosophers TLA+" example and ran it - this seemed to be an affordance of the TLA+ Toolbox GUI which was straightforward to understand.

But then I tried to use the tool with my own. I interpreted the existing code of the dining philosophers and tried to make my own ringbuffer model.

It took me a while that I needed to update this screen to put in the following details that I have filled in on the screenshot:

https://github.com/samsquire/assembly/blob/main/screenshots/...

You have to put your entrypoint in the "temporal formula" and then put your model arguments on the right hand side.

I was able to piece together the operation of this tool by piecing together various reference details together, it wasn't until I saw that screenshot I referenced in my OP that I realised I needed to do that step to get the PlusCal code to update the TLC code that follows it. I was wondering why it didn't work until I saw that screenshot.

Thank you for this in-depth article.

I am a less than a C++ beginner but I asked Stack Overflow how to run C++ coroutines in a thread pool. It seems coroutines in C++20 are unfinalised but don't quote me on that but I did get some sourcecode for older versions of the C++20 standard.

I used Marce's Col's excellent blog post about how to create coroutines in assembly by adjusting the RSP pointer.

https://blog.dziban.net/posts/coroutines/

I extended Marce's code to run the coroutines in kernel threads:

https://github.com/samsquire/assembly (see threadedcoroutines.S)

I have been thinking of coroutines in terms of query compilation for database engines and the volcano query model and this article:

https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html

Tying together two pieces of code that call eachother in push or pull driven style is really powerful. Or if you're running multiple independent tasks that need their own state. This as I understand it is the original intent of object orientation that Alan Kay wanted and is represented by Erlang and partly Go.

Specifically, I am thinking of compiler created coroutines where code can be interleaved at compile time rather than at runtime.

Thank you for your ideas and thoughts.

This might be relevant - I've been playing around with some assembly to unwind the stack, but it occurred to me I don't need to pop the stack to scan through it. So like C++ exception handling (I learned about it in the Itanium C++ ABI) or algebraic effects, you can scan memory if you have access to the stack start in memory (I do that by storing the rsp somewhere in .global main) in theory it's just data.

I need to generate sections of lookup data for range information for associating .text code section addresses with function names.

In theory this would also be useful for coroutines since a coroutine position/state is just a program counter position of code that you can JMP to in your yield function (that isn't a call but an offset)

To move a coroutine from one thread to another or another machine over the network or persist to disk, let me think. We could do what C++ coroutines does and have a promise struct object that is presumably on the stack when a coroutine resumes by jumping to that coroutines location.

I think the hard part is being stackless and persisting the current coroutine state. You could mov $COMPILER_DETERMINED_OFFSET into -10(%rbp) that promise object and then when the coroutine resumes it does a JMP -10(%rbp) in a label before the coroutine body.

I am a beginner to assembly programming but here is my program: https://github.com/samsquire/assembly/blob/main/stackunwind....

https://github.com/samsquire/assembly/blob/main/coroutines.S

This might be useful to someone who wants to port this to C. This uses the stack switching idea. So they are stackful coroutines.

There's also Tina a header only coroutine library