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fix ConcurrentModificationException in async command sending #13626

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fix ConcurrentModificationException in async command sending #13626

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e21ef2a
fix ConcurrentModificationException in async command sending
Gerrygames Feb 11, 2026
4733cfa
minor comment fix
Warriorrrr Feb 14, 2026
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33 changes: 13 additions & 20 deletions paper-server/patches/sources/net/minecraft/commands/Commands.java.patch
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Original file line number Diff line number Diff line change
Expand Up @@ -134,7 +134,7 @@
}

return null;
@@ -409,17 +_,110 @@
@@ -409,17 +_,113 @@
}

public void sendCommands(ServerPlayer player) {
Expand All @@ -147,9 +147,10 @@
+ // CraftBukkit start
+ // Register Vanilla commands into builtRoot as before
+ // Paper start - Perf: Async command map building
+ // Copy root children to avoid concurrent modification during building
+ final java.util.Collection<CommandNode<CommandSourceStack>> commandNodes = new java.util.ArrayList<>(this.dispatcher.getRoot().getChildren());
+ COMMAND_SENDING_POOL.execute(() -> this.sendAsync(player, commandNodes));
+ // Copy root node to avoid concurrent modification during building
+ final RootCommandNode<CommandSourceStack> rootNode = new RootCommandNode<>();
+ this.dispatcher.getRoot().getChildren().forEach(rootNode::addChild);
+ COMMAND_SENDING_POOL.execute(() -> this.sendAsync(player, rootNode));
+ }
+
+ // Fixed pool, but with discard policy
Expand All @@ -163,13 +164,16 @@
+ new java.util.concurrent.ThreadPoolExecutor.DiscardPolicy()
+ );
+
+ private void sendAsync(ServerPlayer player, java.util.Collection<CommandNode<CommandSourceStack>> dispatcherRootChildren) {
+ private void sendAsync(ServerPlayer player, RootCommandNode<CommandSourceStack> dispatcherRoot) {
+ // Paper end - Perf: Async command map building
Map<CommandNode<CommandSourceStack>, CommandNode<CommandSourceStack>> map = new HashMap<>();
RootCommandNode<CommandSourceStack> rootCommandNode = new RootCommandNode<>();
map.put(this.dispatcher.getRoot(), rootCommandNode);
- map.put(this.dispatcher.getRoot(), rootCommandNode);
- fillUsableCommands(this.dispatcher.getRoot(), rootCommandNode, player.createCommandSourceStack(), map);
+ fillUsableCommands(dispatcherRootChildren, rootCommandNode, player.createCommandSourceStack(), map); // Paper - Perf: Async command map building; pass copy of children
+ // Paper start - Perf: Async command map building; pass copy of root
+ map.put(dispatcherRoot, rootCommandNode);
+ fillUsableCommands(dispatcherRoot, rootCommandNode, player.createCommandSourceStack(), map);
+ // Paper end - Perf: Async command map building; pass copy of root
+
+ java.util.Collection<String> bukkit = new java.util.LinkedHashSet<>();
+ for (CommandNode node : rootCommandNode.getChildren()) {
Expand Down Expand Up @@ -198,10 +202,8 @@
player.connection.send(new ClientboundCommandsPacket(rootCommandNode, COMMAND_NODE_INSPECTOR));
}

- private static <S> void fillUsableCommands(CommandNode<S> root, CommandNode<S> current, S source, Map<CommandNode<S>, CommandNode<S>> output) {
- for (CommandNode<S> commandNode : root.getChildren()) {
+ private static <S> void fillUsableCommands(java.util.Collection<CommandNode<S>> children, CommandNode<S> current, S source, Map<CommandNode<S>, CommandNode<S>> output) { // Paper - Perf: Async command map building; pass copy of children
+ for (CommandNode<S> commandNode : children) { // Paper - Perf: Async command map building; pass copy of children
private static <S> void fillUsableCommands(CommandNode<S> root, CommandNode<S> current, S source, Map<CommandNode<S>, CommandNode<S>> output) {
for (CommandNode<S> commandNode : root.getChildren()) {
+ // Paper start - Brigadier API
+ if (commandNode.clientNode != null) {
+ commandNode = commandNode.clientNode;
Expand Down Expand Up @@ -248,12 +250,3 @@
if (argumentBuilder.getRedirect() != null) {
argumentBuilder.redirect(output.get(argumentBuilder.getRedirect()));
}
@@ -428,7 +_,7 @@
output.put(commandNode, commandNode1);
current.addChild(commandNode1);
if (!commandNode.getChildren().isEmpty()) {
- fillUsableCommands(commandNode, commandNode1, source, output);
+ fillUsableCommands(commandNode.getChildren(), commandNode1, source, output); // Paper - Perf: Async command map building; pass copy of children
}
}
}
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