Multithreaded WASM

[calm stag]

I would like to write multithreaded WASM using Zig. I know that multithreaded WASM can be achieved by spawning multiple Web Workers, then giving them all the same WebAssembly.Memory backed by a SharedArrayBuffer. Workers can synchronize and communicate using atomics.

Questions I have:

• What about the stack space per thread? Since all threads use the same memory, their stacks must not overlap. How do I control this?
• Are there any synchronization primitives built-in that can help me, or must I handroll all of it? (thinking mutexes, etc.)
• What things are thread safe? Is the wasm allocator thread safe? If not, do I need to wrap allocations in my own mutex?

[storm coyote]

I don't know anything about wasm but on question 3, https://ziglang.org/documentation/0.16.0/std/#std.heap.WasmAllocator unfortunately

[calm stag]

What is a BrkAllocator?

Ah well, I can just use BrkAllocator then. If I have a mutex, I can just build my own allocator that, for every operation, locks the mutex and then forwards to the underlying allocator, no? Then I'm good!

[storm coyote]

it gets memory by extending the low part of the address space (the high part being the stack). That's how it was done in old unix OSes (and wasm apparently)

I suppose you can do that, yes