How to enforce Lua scripts runtime limit?

Question

Running an almost trivial script in lua with dofile, 10000 times, takes about 52 seconds in this machine, but if i run 10000 times "lua52 script.lua", it takes 3 or 4 times more. I'm aware that there's more system calls involved and other overhead, but what i try to achieve is running scripts with a timeout of let's say 3 seconds, and print out the output. My problem is scripts with infinite loops, intentional or not, for example:

while(true) do
end

Can i make a timeout for a dofile from within Lua? Is my only option to call the interpreter each time with timeout(3)?

Answer 1

It feels a bit wrong for a novice like me to be correcting lhf on Lua matters, but here goes; passing "count" to debug.sethook is the same as passing "c" or "call", the correct mask to pass to fire the associated function after n VM instructions is "".

As such, to restrict the runtime of code loaded from dofile(), use something like the following:

local f = function() error("timeout") end
local x,y = xpcall(function()
  debug.sethook(f, "", 1e8)
  local ret = dofile("script.lua")
  debug.sethook()
  return ret
end, debug.traceback)

Answer 2

If you don't call out to C functions in your scripts you can use the count hook with a large count value and raise an error inside the hook:

local function f() error"timeout!" end
debug.sethook(f,"count",1e6)
while true do end

In your application, set the count hook before calling dofile.

The count hook is called every n Lua VM instructions. However, there is not way to account for the time taken in C functions, hence my caveat above.