Unusual error and crash.

[jhcole]

Running 90e08fe. I can't figure out how line falling_snow.lua:98 is fine but then it chokes on 109. I've only seen this error once.

2016-08-10 04:17:41: ERROR[Main]: ServerError: Runtime error from mod 'snow' in callback environment_Step(): /home/foz/.minetest/mods/snow/src/falling_snow.lua:109: attempt to index a nil value
2016-08-10 04:17:41: ERROR[Main]: stack traceback:
2016-08-10 04:17:41: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:109: in function 'cold_perlin_test'
2016-08-10 04:17:41: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:137: in function 'get_snow'
2016-08-10 04:17:41: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:226: in function 'step_func'
2016-08-10 04:17:41: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:274: in function </home/foz/.minetest/mods/snow/src/falling_snow.lua:273>
2016-08-10 04:17:41: ERROR[Main]: /usr/local/share/minetest/builtin/game/register.lua:369: in function </usr/local/share/minetest/builtin/game/register.lua:349>

[HybridDog]

minetest-mod-snow/src/falling_snow.lua

Line 88 in 90e08fe

-- cache perlin noise tests

The metatable of cold_perl_values is changed, maybe the garbage collector deleted cold_perl_values[y] when minetest.get_perlin took memory.
Actually it should know that cold_perl_values[y][x] is accessed there and avoid deleting it, shouldn't it?

[jhcole]

I thought it might be related to garbage collection, but I would have hoped Lua would know better. Its very confusing to me at the moment what happened.

[jhcole]

It happened again :(

2016-08-14 13:34:58: ERROR[Main]: ServerError: Runtime error from mod 'snow' in callback environment_Step(): /home/foz/.minetest/mods/snow/src/falling_snow.lua:109: attempt to index a nil value
2016-08-14 13:34:58: ERROR[Main]: stack traceback:
2016-08-14 13:34:58: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:109: in function 'cold_perlin_test'
2016-08-14 13:34:58: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:137: in function 'get_snow'
2016-08-14 13:34:58: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:226: in function 'step_func'
2016-08-14 13:34:58: ERROR[Main]: /home/foz/.minetest/mods/snow/src/falling_snow.lua:274: in function </home/foz/.minetest/mods/snow/src/falling_snow.lua:273>
2016-08-14 13:34:58: ERROR[Main]: /usr/local/share/minetest/builtin/game/register.lua:369: in function </usr/local/share/minetest/builtin/game/register.lua:349>

[HybridDog]

Maybe minetest.get_perlin takes lots of memory.
l now assume the garbage collector does not know that it is used there.
Anyway, if it removes cold_perl_values[y], it needs memory, so it should not cache v if it happened: 30b0dd9

Strangely your error message is attempt to index a nil value, i.e. x or y is nil (somehow?) but if the field was nil, e.g. due to garbage collection, the error message would be different: attempt to index field '?' (a nil value).
If it still crashes, it now tells at least if y (or both) (L109) or only x (L110) becomes nil, please inform me.

[rubenwardy]

try adding

if x == nil then
    error("nil x")
end
if y == nil then
    error("ni y")
end

to

minetest-mod-snow/src/falling_snow.lua

Line 97 in 90e08fe

and seeing if that causes it to crash due to either of them being nil

[HybridDog]

rubenwardy, as long as this can't be reproduced, the code doesn't help much

x and y is passed to l_get2d, which copies the values to NoisePerlin2D l assume

[HybridDog]

but this crashes as soon as a the first player joins the server.

2016-08-20 06:23:59: ERROR[Main]: ServerError: Runtime error from mod 'snow' in callback environment_Step(): .../foz/Code/minetest/bin/../mods/snow/src/falling_snow.lua:122: x no integer but 38.588001251221 y no integer but -43.385997772217
2016-08-20 06:23:59: ERROR[Main]: stack traceback:
2016-08-20 06:23:59: ERROR[Main]: [C]: in function 'error'
2016-08-20 06:23:59: ERROR[Main]: .../foz/Code/minetest/bin/../mods/snow/src/falling_snow.lua:122: in function 'cold_perlin_test'
2016-08-20 06:23:59: ERROR[Main]: .../foz/Code/minetest/bin/../mods/snow/src/falling_snow.lua:155: in function 'get_snow'
2016-08-20 06:23:59: ERROR[Main]: .../foz/Code/minetest/bin/../mods/snow/src/falling_snow.lua:244: in function 'step_func'
2016-08-20 06:23:59: ERROR[Main]: .../foz/Code/minetest/bin/../mods/snow/src/falling_snow.lua:292: in function <.../foz/Code/minetest/bin/../mods/snow/src/falling_snow.lua:291>
2016-08-20 06:23:59: ERROR[Main]: /home/foz/Code/minetest/bin/../builtin/game/register.lua:369: in function

l think l forgot to round the player position, so the cache didn't work and
l assume because float numbers are inaccurate in lua, the indices change slightly.

[jhcole]

I deployed the latest (b1a7d12) a week ago and haven't seen it happen again so hopefully it is fixed. I have, however, run out of memory twice in the last week #22