Use SingleThreadScheduler in Folia

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/BukkitScheduler.java

@@ -0,0 +1,39 @@
+package com.turikhay.mc.mapmodcompanion.spigot;
+
+import org.bukkit.plugin.Plugin;
+
+import java.util.logging.Level;
+
+public class BukkitScheduler implements PluginScheduler {
+    private final Plugin plugin;
+
+    public BukkitScheduler(Plugin plugin) {
+        this.plugin = plugin;
+    }
+
+    @Override
+    public void cleanUp() {
+    }
+
+    @Override
+    public void schedule(Runnable r) {
+        if (plugin.getServer().isPrimaryThread()) {
+            executeTask(r);
+        } else {
+            plugin.getServer().getScheduler().scheduleSyncDelayedTask(this.plugin, () -> executeTask(r));
+        }
+    }
+
+    private void executeTask(Runnable r) {
+        try {
+            r.run();
+        } catch (Throwable t) {
+            plugin.getLogger().log(Level.SEVERE, "Failed to execute the task", t);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "BukkitScheduler{}";
+    }
+}

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/FoliaSupport.java

@@ -0,0 +1,18 @@
+package com.turikhay.mc.mapmodcompanion.spigot;
+
+public class FoliaSupport {
+    private static Boolean IS_FOLIA_SERVER;
+
+    public static boolean isFoliaServer() {
+        if (IS_FOLIA_SERVER == null) {
+            boolean isIt = true;
+            try {
+                Class.forName("io.papermc.paper.threadedregions.RegionizedServer");
+            } catch (Throwable t) {
+                isIt = false;
+            }
+            IS_FOLIA_SERVER = isIt;
+        }
+        return IS_FOLIA_SERVER;
+    }
+}

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/MapModCompanion.java

@@ -38,6 +38,7 @@ public class MapModCompanion extends JavaPlugin {
     );
 
     private VerboseLogger logger;
+    private PluginScheduler scheduler;
     private ScheduledExecutorService fileChangeWatchdogScheduler;
     private IdRegistry registry;
     private @Nullable ProtocolLib protocolLib;
@@ -63,16 +64,18 @@ public void onLoad() {
 
     @Override
     public void onEnable() {
+        scheduler = initScheduler();
         fileChangeWatchdogScheduler = FileChangeWatchdog.createScheduler(ILogger.ofJava(logger));
         new Metrics(this, BSTATS_ID);
         saveDefaultConfig();
-        load();
+        scheduler.schedule(this::load);
     }
 
     @Override
     public void onDisable() {
-        unload();
+        scheduler.schedule(this::unload);
         fileChangeWatchdogScheduler.shutdown();
+        scheduler.cleanUp();
     }
 
     private void load() {
@@ -90,7 +93,7 @@ private void load() {
                 logger,
                 fileChangeWatchdogScheduler,
                 getDataFolder().toPath().resolve("config.yml"),
-                () -> getServer().getScheduler().scheduleSyncDelayedTask(this, this::reload)
+                () -> scheduler.schedule(this::reload)
         );
         fileChangeWatchdog.start();
     }
@@ -108,6 +111,18 @@ private void reload() {
         load();
     }
 
+    private PluginScheduler initScheduler() {
+        PluginScheduler selected;
+        if (FoliaSupport.isFoliaServer()) {
+            logger.info("Folia server support enabled");
+            selected = new SingleThreadScheduler(ILogger.ofJava(logger));
+        } else {
+            selected = new BukkitScheduler(this);
+        }
+        logger.fine("Scheduler: " + selected);
+        return selected;
+    }
+
     private IdRegistry initRegistry() {
         World world = null;
         if (getConfig().getBoolean("preferDefaultWorld", true)) {

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/PluginScheduler.java

@@ -0,0 +1,7 @@
+package com.turikhay.mc.mapmodcompanion.spigot;
+
+import com.turikhay.mc.mapmodcompanion.Disposable;
+
+public interface PluginScheduler extends Disposable {
+    void schedule(Runnable r);
+}

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/SingleThreadScheduler.java

@@ -0,0 +1,36 @@
+package com.turikhay.mc.mapmodcompanion.spigot;
+
+import com.turikhay.mc.mapmodcompanion.DaemonThreadFactory;
+import com.turikhay.mc.mapmodcompanion.ILogger;
+
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+
+public class SingleThreadScheduler implements PluginScheduler {
+
+    private final ScheduledThreadPoolExecutor service;
+
+    public SingleThreadScheduler(ILogger logger) {
+        this.service = new ScheduledThreadPoolExecutor(
+                1,
+                new DaemonThreadFactory(logger, SingleThreadScheduler.class)
+        );
+        service.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
+    }
+
+    @Override
+    public void cleanUp() {
+        service.shutdown();
+    }
+
+    @Override
+    public void schedule(Runnable r) {
+        service.submit(r);
+    }
+
+    @Override
+    public String toString() {
+        return "SingleThreadScheduler{" +
+                "service=" + service +
+                '}';
+    }
+}