avoid locking in generated function preamble

Author: MilesCranmer

src/Convert/pyconvert.jl

@@ -309,8 +309,9 @@ pyconvert_fix(::Type{T}, func) where {T} = x -> func(T, x)
 
 const PYCONVERT_RULES_CACHE = Lockable(Dict{Type,Dict{C.PyPtr,Vector{Function}}}())
 
-@generated pyconvert_rules_cache(::Type{T}) where {T} =
-    Base.@lock PYCONVERT_RULES_CACHE get!(Dict{C.PyPtr,Vector{Function}}, PYCONVERT_RULES_CACHE[], T)
+pyconvert_rules_cache(::Type{T}) where {T} =
+    Base.@lock PYCONVERT_RULES_CACHE _pyconvert_rules_cache!(PYCONVERT_RULES_CACHE[], T)
+@generated _pyconvert_rules_cache!(d::Dict, ::Type{T}) where {T} = get!(Dict{C.PyPtr,Vector{Function}}, d, T)
 
 function pyconvert_rule_fast(::Type{T}, x::Py) where {T}
     if T isa Union