Lock only once for multiple accesses

[Borketh]

As per our previous convo through discord, I have a proposal for reducing the number of times App needs to be locked for access to fields. Here it is:

struct Singleton
    # what's in here doesn't matter
    number::Int
    bool::Bool
    symbol::Symbol
    Singleton(; number::Int=0, bool::Bool=false, symbol::Symbol=:hi) = begin
        if !isassigned(singleton)
            singleton[] = new(number, bool, symbol)
        end
        
        return sng_lock, singleton
    end
end

global const singleton = Ref{Singleton}()
global const sng_lock = ReentrantLock()

# Locked Multiple Field Access Operator
function LMFAO(lk::ReentrantLock, objref::Base.RefValue{T}, fields::Symbol...) where T
    @assert typeof(lk) === ReentrantLock
    @lock lk let obj::T = objref[]
        stuff = NTuple{length(fields), Any}(getfield(obj, f) for f in fields)
    end
end

macro LMFAO(lk::Symbol, objref::Symbol, fields::Symbol...) 
    @info "Variable method"
    quote LMFAO($lk, $objref, $fields...) end
end

macro LMFAO(call::Expr, fields::Symbol...)
    @info "Call method"
    quote LMFAO(eval($call)..., $fields...) end 
end


n, b, sy = @LMFAO Singleton() number bool symbol # these don't have to be in order
@info n b sy

lk, sg = Singleton()
n, b, sy = @LMFAO lk sg number bool symbol
@info lk sg
@info n b sy

In theory this locks once to retrieve the struct and then the fields requested.
If the informality of the macro-acronym (macronym?) is too much I'll think of something else.

[jhigginbotham64]

This seems like a neat idea, but I'm going to wait to work on it until I've settled how multi-app is going to be handled. Singletons should be going away in v0.3.0, so I don't want to invest too heavily in beautifying them just yet.

[Borketh]

I intend to make a package called LockedStructs.jl that uses this and a couple other things pending, which you may be able to use. If all goes well it should be ready for the registry by the weekend.

[jhigginbotham64]

I've been working on v0.3.0 and it's not done yet but already there are no more locks. Hence no need for this issue.