Dynamic Trees Crash (Exception ticking world) (BasicBranchBlock.checkForRot)

[lavatrout]

Summary

Crash occurs on dedicated server during world generation via Chunky. Crash report says:

• Exception ticking world
• spammed strack trace: com.ferreusveritas.dynamictrees.block.branch.BasicBranchBlock.checkForRot(BasicBranchBlock.java:169) ~[DynamicTrees-1.20.1-1.4.9.jar%23695!/:1.20.1-1.4.9] {re:classloading}

Details

I am running a dedicated server for the modpack: Minecolonies Create and Conquer. I added a few mods to the modpack (Chunky, All the Leaks, Sparky, etc) to make server hosting easier and less resource intensive.

We were playing on the server with no issues until a bug cropped up in the version of Minecolonies we were using. I updated the version of minecolonies (and its dependents), and while I was at it, added distant horizons. The minecolonies bug was fixed, but stuttering lag made the game difficult to play.

When we were done, I restarted the server and ran chunky over night hoping that pregenerating the world would resolve the lag spikes. However, the server experienced a tick that took over 120 seconds to complete, and it crashed. The crash report contains repeated calls to block.branch.BasicBranchBlock.checkForRot. This looks like a stack overflow to me, but I don't have enough context be certain.

Below is a section of the console output:

[03:18:29] [Server Watchdog/ERROR] [minecraft/ServerWatchdog]: A single server tick took 120.00 seconds (should be max 0.05)
[03:18:29] [Server Watchdog/ERROR] [minecraft/ServerWatchdog]: Considering it to be crashed, server will forcibly shutdown.
[03:18:30] [Server Watchdog/FATAL] [ne.mi.co.ForgeMod/]: Preparing crash report with UUID 8096a5e9-c1d1-4bce-974f-14381a5e2f35
[03:18:30] [Server Watchdog/FATAL] [ne.mi.co.ForgeMod/]: Preparing crash report with UUID da87fc3f-a0e9-464d-a9cf-7a57b6a883bf
[03:18:30] [Server Watchdog/ERROR] [minecraft/ServerWatchdog]: This crash report has been saved to: C:\Users\anher\Documents\mcss_win-x86-64_v13.10.0\servers\Minecolonies_C&C\.\crash-reports\crash-2026-04-13_03.18.30-server.txt

The server generated two crash reports. The first crash report contains the Dynamic Trees stack trace. The second crash report was generated by the Server Watchdog. Both are included below.

Steps to Reproduce

To be included once found...

Mod Version

• Dynamic Trees version: 1.20.1-1.4.9
• Mods and additional add-ons included in crash report. Due to compatibility issues, several mods are not fully up to date.

Reports

Dynamic Trees crash report: https://gist.github.com/lavatrout/2c61779eca3e1cdb04f65c15cef61ebc
Server Watchdog crash report: https://gist.github.com/lavatrout/ad05e8f635fdcedf0b8775d17cc39918

[lavatrout]

Update: I can reproduce the crash by loading a specific chunk in my world. It appears to be an issue with a specific tree (or trees). I suspect the problem is with the tree's shape (either the branches turn around in a circle or two trunks share a branch... im not sure) and the rot code gets stuck in an infinite recursion. I wish I had the know-how to look at the generated tree pre-rot, but I don't. I can't even get my character near it before the game crashes.

I did figure out a code change that fixes the crash on my end by changing the code in BasicBranchBlock.java to this:

    //assigns hash value to each position to prevent infinite recursion in the case of a loop in the branch network.  This can happen when branches are placed in a circle, or when a branch grows back into itself.
    @Override
    public boolean checkForRot(LevelAccessor level, BlockPos pos, Species species, int fertility, int radius, RandomSource rand, float chance, boolean rapid) {
        return checkForRotInternal(level, pos, species, fertility, radius, rand, chance, rapid, new HashSet<>());
    }

    // Internal version that tracks visited positions to avoid infinite recursion
    private boolean checkForRotInternal(LevelAccessor level, BlockPos pos, Species species, int fertility, int radius, RandomSource rand, float chance, boolean rapid, Set<BlockPos> visited) {

        if (visited.contains(pos)) {
            return false; // already processing/processed this position -> avoid recursion loop
        }
        visited.add(pos);

        if (!rapid && (chance == 0.0f || rand.nextFloat() > chance)) {
            return false; // Bail out if not in rapid mode and the postRot chance fails
        }

        int neigh = 0; // High Nybble is count of branches, Low Nybble is any reinforcing treepart(including branches)

        for (Direction dir : Direction.values()) {
            BlockPos deltaPos = pos.relative(dir);
            BlockState deltaBlockState = level.getBlockState(deltaPos);
            neigh += TreeHelper.getTreePart(deltaBlockState).branchSupport(deltaBlockState, level, this, deltaPos, dir, radius);
            if (getBranchSupport(neigh) >= 1 && getLeavesSupport(neigh) >= 2) { // Need two neighbors.. one of which must be another branch
                return false; // Reinforced, no rot
            }
        }

        boolean didRot = species.rot(level, pos, neigh & 0x0F, radius, fertility, rand, rapid, fertility > 0);

        if (rapid && didRot) { // Speedily postRot back dead branches if this block rotted
            for (Direction dir : Direction.values()) {
                BlockPos neighPos = pos.relative(dir);
                BlockState neighState = level.getBlockState(neighPos);
                // Only recurse into same branch type and skip already visited positions to prevent infinite recursion
                if (neighState.getBlock() == this && !visited.contains(neighPos)) {
                    this.checkForRotInternal(level, neighPos, species, fertility, getRadius(neighState), rand, 1.0f, true, visited);
                }
            }
        }

        return didRot;
    }

I don't know if a change like this would affect the rest of the code, but feel free to use that if you want 👍