Hi list.
Why the following use of a ephemeron table to keep a chain of weakly referenced values degradates the GC performance?
local weakkeys = setmetatable({}, { __mode = "k" })
local strong = {}
for i = 1, 1e5 do
local value = {}
weakkeys[value] = strong
strong = value
end
These are the times such script takes to execute in my machine in the different versions of Lua with support for ephemerons:
Lua 5.2.4
real 0m7.222s
user 0m7.192s
sys 0m0.000s
Lua 5.3.5
real 0m42.718s
user 0m42.656s
sys 0m0.028s
Lua 5.4.0-alpha
real 2m26.025s
user 2m25.892s
sys 0m0.032s
The following code creates a similar reference structure,
local weakkeys = setmetatable({}, { __mode = "k" })
local strong = {}
for i = 1, 1e5 do
local value = {strong}
weakkeys[value] = true
strong = value
end
but the GC goes back to its normal performance:
Lua 5.2.4
real 0m0.075s
user 0m0.064s
sys 0m0.008s
Lua 5.3.5
real 0m0.068s
user 0m0.056s
sys 0m0.012s
Lua 5.4.0-alpha
real 0m0.062s
user 0m0.056s
sys 0m0.004s
Any insight is very welcome.
