fix: snapshot entity metrics on main thread

src/main/java/com/prometheus/spigot/metrics/MetricsRegistry.java

@@ -6,6 +6,7 @@ import java.lang.management.MemoryUsage;
 import java.lang.management.ThreadMXBean;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
@@ -31,6 +32,8 @@ public final class MetricsRegistry {
     private final Method serverMsptMethod;
     private final Method playerPingMethod;
     private final Method chunkTileEntitiesMethod;
+    private volatile Map<String, Long> entityCountsSnapshot = Collections.emptyMap();
+    private volatile Map<String, Long> tileEntityCountsSnapshot = Collections.emptyMap();
 
     private final LongAdder chatMessages = new LongAdder();
     private final LongAdder playerMovements = new LongAdder();
@@ -120,6 +123,37 @@ public final class MetricsRegistry {
         pluginDisables.increment();
     }
 
+    public void refreshEntitySnapshots() {
+        Map<String, Long> entityCounts = new HashMap<>();
+        Map<String, Long> tileCounts = new HashMap<>();
+
+        for (var world : server.getWorlds()) {
+            for (Entity entity : world.getEntities()) {
+                EntityType type = entity.getType();
+                String label = normalizeLabel(type.name());
+                entityCounts.merge(label, 1L, Long::sum);
+            }
+
+            if (chunkTileEntitiesMethod != null) {
+                for (Chunk chunk : world.getLoadedChunks()) {
+                    Object result = invoke(chunkTileEntitiesMethod, chunk);
+                    if (!(result instanceof Object[] states)) {
+                        continue;
+                    }
+                    for (Object state : states) {
+                        if (state instanceof BlockState blockState) {
+                            String label = normalizeLabel(blockState.getType().name());
+                            tileCounts.merge(label, 1L, Long::sum);
+                        }
+                    }
+                }
+            }
+        }
+
+        entityCountsSnapshot = Collections.unmodifiableMap(entityCounts);
+        tileEntityCountsSnapshot = Collections.unmodifiableMap(tileCounts);
+    }
+
     public String render() {
         StringBuilder builder = new StringBuilder();
 
@@ -226,37 +260,14 @@ public final class MetricsRegistry {
     }
 
     private void appendEntityMetrics(StringBuilder builder) {
-        Map<String, Long> entityCounts = new HashMap<>();
-        for (var world : server.getWorlds()) {
-            for (Entity entity : world.getEntities()) {
-                EntityType type = entity.getType();
-                String label = normalizeLabel(type.name());
-                entityCounts.merge(label, 1L, Long::sum);
-            }
-        }
-        appendLabeledGauge(builder, "spigot_entities_total", "Entities by type", "type", entityCounts);
+        appendLabeledGauge(builder, "spigot_entities_total", "Entities by type", "type", entityCountsSnapshot);
     }
 
     private void appendTileEntityMetrics(StringBuilder builder) {
         if (chunkTileEntitiesMethod == null) {
             return;
         }
-        Map<String, Long> tileCounts = new HashMap<>();
-        for (var world : server.getWorlds()) {
-            for (Chunk chunk : world.getLoadedChunks()) {
-                Object result = invoke(chunkTileEntitiesMethod, chunk);
-                if (!(result instanceof Object[] states)) {
-                    continue;
-                }
-                for (Object state : states) {
-                    if (state instanceof BlockState blockState) {
-                        String label = normalizeLabel(blockState.getType().name());
-                        tileCounts.merge(label, 1L, Long::sum);
-                    }
-                }
-            }
-        }
-        appendLabeledGauge(builder, "spigot_tile_entities_total", "Tile entities by type", "type", tileCounts);
+        appendLabeledGauge(builder, "spigot_tile_entities_total", "Tile entities by type", "type", tileEntityCountsSnapshot);
     }
 
     private void appendPlayerPingMetrics(StringBuilder builder) {