Why is Json parsing slower in multiple threads?

[Andrej Mitrovic]

On Wednesday, 21 June 2023 at 00:35:42 UTC, Steven Schveighoffer 
wrote:
> The D GC has a single global lock to allocate memory -- even 
> memory that might be on a free list. So the threads are all 
> bottlenecked on waiting their turn for the lock.

This would be something that's important enough to list on the 
spec page for the GC: https://dlang.org/spec/garbage.html

It's only mentioned in passing here: 
https://dlang.org/articles/d-array-article.html#caching
in the sentence "not to mention acquiring the global GC lock".

In theory the GC is replaceable but I think we should document 
the behavior of the default one.

I'll submit an issue for it.