Multithreading for command system

Author: Zabuzard

application/src/main/java/org/togetherjava/tjbot/commands/SlashCommand.java

@@ -92,6 +92,10 @@ public interface SlashCommand {
      * Triggered by the command system when a slash command corresponding to this implementation
      * (based on {@link #getData()} has been triggered.
      * <p>
+     * This method may be called multi-threaded. In particular, there are no guarantees that it will
+     * be executed on the same thread repeatedly or on the same thread that other event methods have
+     * been called on.
+     * <p>
      * Details are available in the given event and the event also enables implementations to
      * respond to it.
      * <p>
@@ -134,6 +138,10 @@ public interface SlashCommand {
      * Triggered by the command system when a button corresponding to this implementation (based on
      * {@link #getData()} has been clicked.
      * <p>
+     * This method may be called multi-threaded. In particular, there are no guarantees that it will
+     * be executed on the same thread repeatedly or on the same thread that other event methods have
+     * been called on.
+     * <p>
      * Details are available in the given event and the event also enables implementations to
      * respond to it.
      * <p>
@@ -150,6 +158,10 @@ public interface SlashCommand {
      * Triggered by the command system when a selection menu corresponding to this implementation
      * (based on {@link #getData()} has been clicked.
      * <p>
+     * This method may be called multi-threaded. In particular, there are no guarantees that it will
+     * be executed on the same thread repeatedly or on the same thread that other event methods have
+     * been called on.
+     * <p>
      * Details are available in the given event and the event also enables implementations to
      * respond to it.
      * <p>

application/src/main/java/org/togetherjava/tjbot/commands/system/CommandSystem.java

@@ -22,6 +22,8 @@
 import org.togetherjava.tjbot.db.Database;
 
 import java.util.*;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -40,6 +42,7 @@
 public final class CommandSystem extends ListenerAdapter implements SlashCommandProvider {
     private static final Logger logger = LoggerFactory.getLogger(CommandSystem.class);
     private static final String RELOAD_COMMAND = "reload";
+    private static final ExecutorService COMMAND_SERVICE = Executors.newCachedThreadPool();
     private final Map<String, SlashCommand> nameToSlashCommands;
 
     /**
@@ -80,7 +83,9 @@ public CommandSystem(@NotNull Database database) {
     public void onReady(@NotNull ReadyEvent event) {
         // Register reload on all guilds
         logger.debug("JDA is ready, registering reload command");
-        event.getJDA().getGuildCache().forEach(this::registerReloadCommand);
+        event.getJDA()
+            .getGuildCache()
+            .forEach(guild -> COMMAND_SERVICE.execute(() -> registerReloadCommand(guild)));
         // NOTE We do not have to wait for reload to complete for the command system to be ready
         // itself
         logger.debug("Command system is now ready");
@@ -90,21 +95,22 @@ public void onReady(@NotNull ReadyEvent event) {
     public void onSlashCommand(@NotNull SlashCommandEvent event) {
         logger.debug("Received slash command '{}' (#{}) on guild '{}'", event.getName(),
                 event.getId(), event.getGuild());
-        requireSlashCommand(event.getName()).onSlashCommand(event);
+        COMMAND_SERVICE.execute(() -> requireSlashCommand(event.getName()).onSlashCommand(event));
     }
 
     @Override
     public void onButtonClick(@NotNull ButtonClickEvent event) {
         logger.debug("Received button click '{}' (#{}) on guild '{}'", event.getComponentId(),
                 event.getId(), event.getGuild());
-        forwardComponentCommand(event, SlashCommand::onButtonClick);
+        COMMAND_SERVICE.execute(() -> forwardComponentCommand(event, SlashCommand::onButtonClick));
     }
 
     @Override
     public void onSelectionMenu(@NotNull SelectionMenuEvent event) {
         logger.debug("Received selection menu event '{}' (#{}) on guild '{}'",
                 event.getComponentId(), event.getId(), event.getGuild());
-        forwardComponentCommand(event, SlashCommand::onSelectionMenu);
+        COMMAND_SERVICE
+            .execute(() -> forwardComponentCommand(event, SlashCommand::onSelectionMenu));
     }
 
     private void registerReloadCommand(@NotNull Guild guild) {