fix: multiple ConcurrentModificationException in plugin

Author: Ingrim4

orebfuscator-core/src/main/java/dev/imprex/orebfuscator/proximity/ProximitySystem.java

@@ -45,33 +45,38 @@ public void start() {
   public void run() {
     long processStart = System.nanoTime();
     invokeProcess().whenComplete((v, throwable) -> {
-      if (throwable != null) {
-        OfcLogger.error("An error occurred while running proximity worker", throwable);
-      }
-
-      if (this.executor.isShutdown()) {
-        return;
-      }
-
-      long processTime = System.nanoTime() - processStart;
-      this.statistics.proximityProcess.add(processTime);
-
-      // check if we have enough time to sleep
-      long waitTime = Math.max(0, this.checkInterval - processTime);
-      long waitMillis = TimeUnit.NANOSECONDS.toMillis(waitTime);
-
-      if (waitMillis > 0) {
-        // measure wait time
-        this.statistics.proximityWait.add(TimeUnit.MILLISECONDS.toNanos(waitMillis));
-        this.executor.schedule(this, waitMillis, TimeUnit.MILLISECONDS);
-      } else {
-        // Schedule instead of executing directly to break reentrant execution chains of
-        // OrebfuscatorExecutor and avoid potential StackOverflowError.
-        this.executor.schedule(this, 0L, TimeUnit.NANOSECONDS);
-      }
-    }).whenComplete((v, throwable) -> {
-      if (throwable != null) {
-        OfcLogger.error("An error occurred while running proximity worker, can't recover!", throwable);
+      try {
+        if (throwable != null) {
+          OfcLogger.error("An error occurred while running proximity worker", throwable);
+        }
+
+        if (this.executor.isShutdown()) {
+          return;
+        }
+
+        long processTime = System.nanoTime() - processStart;
+        this.statistics.proximityProcess.add(processTime);
+
+        // check if we have enough time to sleep
+        long waitTime = Math.max(0, this.checkInterval - processTime);
+        long waitMillis = TimeUnit.NANOSECONDS.toMillis(waitTime);
+
+        if (waitMillis > 0) {
+          // measure wait time
+          this.statistics.proximityWait.add(TimeUnit.MILLISECONDS.toNanos(waitMillis));
+          this.executor.schedule(this, waitMillis, TimeUnit.MILLISECONDS);
+        } else {
+          // Schedule instead of executing directly to break reentrant execution chains of
+          // OrebfuscatorExecutor and avoid potential StackOverflowError.
+          this.statistics.proximityWait.add(0);
+          this.executor.schedule(this, 0L, TimeUnit.NANOSECONDS);
+        }
+      } catch (Exception e) {
+        OfcLogger.error("An error occurred while scheduling proximity worker", e);
+
+        // backoff for 1sec on reschedule failure
+        this.statistics.proximityWait.add(TimeUnit.SECONDS.toNanos(1));
+        this.executor.schedule(this, 1L, TimeUnit.SECONDS);
       }
     });
   }

orebfuscator-plugin/src/main/java/net/imprex/orebfuscator/iterop/BukkitPlayerAccessorManager.java

@@ -1,11 +1,9 @@
 package net.imprex.orebfuscator.iterop;
 
-import dev.imprex.orebfuscator.interop.PlayerAccessor;
-import dev.imprex.orebfuscator.logging.OfcLogger;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import net.imprex.orebfuscator.Orebfuscator;
+import java.util.concurrent.ConcurrentHashMap;
 import org.bukkit.Bukkit;
 import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
@@ -17,11 +15,13 @@
 import org.bukkit.event.server.PluginDisableEvent;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
+import dev.imprex.orebfuscator.interop.PlayerAccessor;
+import net.imprex.orebfuscator.Orebfuscator;
 
 @NullMarked
 public class BukkitPlayerAccessorManager implements Listener {
 
-  private final Map<Player, BukkitPlayerAccessor> players = new HashMap<>();
+  private final Map<Player, BukkitPlayerAccessor> players = new ConcurrentHashMap<>();
 
   private final Orebfuscator orebfuscator;
   private final BukkitWorldAccessorManager worldManager;

orebfuscator-plugin/src/main/java/net/imprex/orebfuscator/iterop/BukkitWorldAccessorManager.java

@@ -4,6 +4,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import net.imprex.orebfuscator.Orebfuscator;
 import org.bukkit.Bukkit;
 import org.bukkit.World;
@@ -17,7 +18,7 @@
 @NullMarked
 public class BukkitWorldAccessorManager implements Listener {
 
-  private final Map<World, BukkitWorldAccessor> worlds = new HashMap<>();
+  private final Map<World, BukkitWorldAccessor> worlds = new ConcurrentHashMap<>();
 
   private final Orebfuscator orebfuscator;
 

orebfuscator-plugin/src/main/java/net/imprex/orebfuscator/util/WrappedClientboundLevelChunkPacketData.java

@@ -5,6 +5,7 @@
 import com.comphenix.protocol.reflect.accessors.FieldAccessor;
 import com.comphenix.protocol.utility.MinecraftReflection;
 import dev.imprex.orebfuscator.util.BlockPos;
+import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
 import java.util.function.Predicate;
@@ -43,7 +44,8 @@ public void setBuffer(byte[] buffer) {
   }
 
   public void removeBlockEntityIf(Predicate<BlockPos> predicate) {
-    List<?> blockEntities = (List<?>) BLOCK_ENTITIES.get(this.handle);
+    // work on copy only to prevent ConcurrentModificationException
+    List<?> blockEntities = new ArrayList<>((List<?>) BLOCK_ENTITIES.get(this.handle));
     for (Iterator<?> iterator = blockEntities.iterator(); iterator.hasNext(); ) {
       Object blockEntityInfo = iterator.next();
       int packedXZ = (int) PACKED_XZ.get(blockEntityInfo);
@@ -56,5 +58,6 @@ public void removeBlockEntityIf(Predicate<BlockPos> predicate) {
         iterator.remove();
       }
     }
+    BLOCK_ENTITIES.set(this.handle, blockEntities);
   }
 }