Large Lua string allocation/concatenations crashes Lua environment.

[tlubke]

Doing iterative string building like this can lead to issues.

local n = 9

for i=1,n do
  local s = ""
  for i=1,(2^i) do
    s = s.."!"
  end
end

For n = 9, this is fine, but n = 10 appears to hang something in the firmware. LEDs will hold their state, diii continues to show as connected, but all code execution seems to stop. Soft reboot via ^^r doesn't work, but physically reconnecting seems to fix things.

Interesting to note that building one constant string of size 2^10 does not cause the same behavior. Maybe the strings spawned by concatenation are not garbage collected fast enough and cause an out-of-memory failure because of it?

EDIT: Quick calc using the summation formula would mean n=9 => 131,238B and n=10 => 524,800B assuming nothing gets free'd before the end of the loop. n=10 would be more than available SRAM of the Pico 2.

EDIT 2: Yeah, I think garbage collection is the issue. Adding collectgarbage("collect") to the inner for-loop fixes the crash. I don't think this allocation/collection problem is realistically something to fix, but would be nice to keep the Lua environment running if possible.

[tehn]

thanks for taking a look.

i need to do some real benchmarking of the memory limits within this system. will see if i can put in some introspection utilities for better understanding what's going on.

[tehn]

heap has about 220k so i think your assessment makes sense!

i'll update the README to indicate the memory limitations. let me know if you'd like this issue reopened, if there is a proposal for a structural change.

[catfact]

i think this can be fixed, and is worth fixing. i would try using a custom allocator that errors gracefully rather than panicking...