Mention Base.Lockable in "multi-threading.md" (#58107)
When I originally learned about multithreading and locks (and ended up
rewriting
[https://docs.julialang.org/en/v1/manual/multi-threading/#man-using-locks](Using
locks to avoid data-races)), I was puzzled to find that the association
of a lock and a value was the mental task of the programmer, and not the
programmatic task of the program. I made that explicit in that section
of the manual, writing the following:
> Note that the link between a lock and a variable is made by the
programmer, and not the program.
I was therefore very happy to see Base.Lockable introduced in Julia
1.11. What was missing, was any mention of it in the relevant section of
the manual.
This PR adds a subsection under locks (So a forth level of headings, not
sure if that is fine), showcasing and reccomending the use of
Base.Lockable. I have made heavy use of comments in the example, which
breaks with the general style, but adds valuable interpretation along
the way. I am very open restructuring that part in particular.
---------
Co-authored-by: Chengyu Han <cyhan.dev@outlook.com>
Co-authored-by: Neven Sajko <4944410+nsajko@users.noreply.github.com>
Co-authored-by: Oscar Smith <oscardssmith@gmail.com>
