document the optional argument of the `Task` constructor

[nsajko]

The optional Int parameter seems to determine the stack size of the Task, but its not documented at all.

julia/base/task.jl

Line 5 in 1193997

Core.Task(@nospecialize(f), reserved_stack::Int=0) = Core._Task(f, reserved_stack, ThreadSynchronizer())

[nsajko]

The nice thing about making the Task stack size limit public, is that now it'll be possible to run with a smaller size within the test suite of a package, to catch potential issues early, e.g., overly deep recursion.

[vtjnash]

Just as a warning though, you will consume substantially more memory (both physical and virtual) if you use this option, as it forces eager allocation of a stack that may never get used. Use with some care.

[nsajko]

Oh. I didn't think it'd work like that.

[MilesCranmer]

Just as a warning though, you will consume substantially more memory (both physical and virtual) if you use this option, as it forces eager allocation of a stack that may never get used. Use with some care.

It feels surprising that memory is allocated differently between default stack size limit and custom stack size limit. How hard would it be to turn off eager allocations here?

[MilesCranmer]

I'm also confused because

julia> Task(() -> sleep(10), 10 * 1024 ^ 4)  |> schedule |> fetch

doesn't OOM...