It's ugly but it stops OOM

worldedit-bukkit/adapters/adapter-1_21/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/fawe/v1_21_R1/PaperweightGetBlocks.java

@@ -17,6 +17,7 @@ import com.fastasyncworldedit.core.queue.IQueueExtent;
 import com.fastasyncworldedit.core.queue.implementation.QueueHandler;
 import com.fastasyncworldedit.core.queue.implementation.blocks.CharGetBlocks;
 import com.fastasyncworldedit.core.util.MathMan;
+import com.fastasyncworldedit.core.util.MemUtil;
 import com.fastasyncworldedit.core.util.NbtUtils;
 import com.fastasyncworldedit.core.util.collection.AdaptedMap;
 import com.sk89q.worldedit.bukkit.BukkitAdapter;
@@ -430,7 +431,7 @@ public class PaperweightGetBlocks extends CharGetBlocks implements BukkitGetBloc
     }
 
     @Override
-    @SuppressWarnings("rawtypes")
+    @SuppressWarnings({"rawtypes", "unchecked"})
     public synchronized <T extends Future<T>> T call(IQueueExtent<? extends IChunk> owner, IChunkSet set, Runnable finalizer) {
         if (!callLock.isHeldByCurrentThread()) {
             throw new IllegalStateException("Attempted to call chunk GET but chunk was not call-locked.");
@@ -439,6 +440,15 @@ public class PaperweightGetBlocks extends CharGetBlocks implements BukkitGetBloc
         final ServerLevel nmsWorld = serverLevel;
         CompletableFuture<LevelChunk> nmsChunkFuture = ensureLoaded(nmsWorld, chunkX, chunkZ);
         LevelChunk chunk = nmsChunkFuture.getNow(null);
+        if (chunk == null && MemUtil.shouldBeginSlow()) {
+            try {
+                chunk = nmsChunkFuture.get(); // "Artificially" slow FAWE down if memory low as performing the
+            } catch (InterruptedException | ExecutionException e) {
+                LOGGER.error("Could not get chunk at {},{} whilst low memory", chunkX, chunkZ, e);
+                throw new FaweException(
+                        TextComponent.of("Could not get chunk at " + chunkX + "," + chunkZ + " whilst low memory: " + e.getMessage()));
+            }
+        }
         // Run immediately if possible
         if (chunk != null) {
             return internalCall(set, finalizer, chunk, nmsWorld);

worldedit-core/src/main/java/com/fastasyncworldedit/core/Fawe.java

@@ -138,6 +138,7 @@ public class Fawe {
             } catch (Throwable ignored) {
             }
         }, 0);
+        TaskManager.taskManager().repeatAsync(() -> MemUtil.checkAndSetApproachingLimit(), 1);
 
         TaskManager.taskManager().repeat(timer, 1);
 
@@ -417,11 +418,16 @@ public class Fawe {
             final NotificationEmitter ne = (NotificationEmitter) memBean;
 
             ne.addNotificationListener((notification, handback) -> {
+                LOGGER.info("Notification");
                 final long heapSize = Runtime.getRuntime().totalMemory();
                 final long heapMaxSize = Runtime.getRuntime().maxMemory();
                 if (heapSize < heapMaxSize) {
                     return;
                 }
+                LOGGER.info("NNNNNNNNNNNNNNNNNNNNNNNNNNNN");
+                LOGGER.info("NNNNNNNNNNNNNNNNNNNNNNNNNNNN");
+                LOGGER.info("NNNNNNNNNNNNNNNNNNNNNNNNNNNN");
+                LOGGER.info("JJJJJJJJJJJJJJJJJJJJJJJJJJJJ");
                 MemUtil.memoryLimitedTask();
             }, null, null);
 

worldedit-core/src/main/java/com/fastasyncworldedit/core/queue/IQueueExtent.java

@@ -2,9 +2,6 @@ package com.fastasyncworldedit.core.queue;
 
 import com.fastasyncworldedit.core.extent.filter.block.ChunkFilterBlock;
 import com.fastasyncworldedit.core.extent.processor.IBatchProcessorHolder;
-import com.fastasyncworldedit.core.internal.simd.SimdSupport;
-import com.fastasyncworldedit.core.internal.simd.VectorizedCharFilterBlock;
-import com.fastasyncworldedit.core.internal.simd.VectorizedFilter;
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.operation.Operation;
 import com.sk89q.worldedit.math.BlockVector2;
@@ -157,11 +154,7 @@ public interface IQueueExtent<T extends IChunk> extends Flushable, Trimable, ICh
         if (newChunk != null) {
             chunk = newChunk;
             if (block == null) {
-                if (SimdSupport.useVectorApi() && filter instanceof VectorizedFilter) {
-                    block = new VectorizedCharFilterBlock(this);
-                } else {
-                    block = this.createFilterBlock();
-                }
+                block = this.createFilterBlock();
             }
             block.initChunk(chunkX, chunkZ);
             chunk.filterBlocks(filter, block, region, full);

worldedit-core/src/main/java/com/fastasyncworldedit/core/util/MemUtil.java

@@ -9,6 +9,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 public class MemUtil {
 
     private static final AtomicBoolean memory = new AtomicBoolean(false);
+    private static final AtomicBoolean slower = new AtomicBoolean(false);
 
     public static boolean isMemoryFree() {
         return !memory.get();
@@ -28,6 +29,10 @@ public class MemUtil {
         return false;
     }
 
+    public static boolean shouldBeginSlow() {
+        return slower.get();
+    }
+
     public static long getUsedBytes() {
         return Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
     }
@@ -51,6 +56,13 @@ public class MemUtil {
         return size;
     }
 
+    public static void checkAndSetApproachingLimit() {
+        final long heapFreeSize = Runtime.getRuntime().freeMemory();
+        final long heapMaxSize = Runtime.getRuntime().maxMemory();
+        final int size = (int) ((heapFreeSize * 100) / heapMaxSize);
+        slower.set(size > 80);
+    }
+
     private static final Queue<Runnable> memoryLimitedTasks = new ConcurrentLinkedQueue<>();
     private static final Queue<Runnable> memoryPlentifulTasks = new ConcurrentLinkedQueue<>();