Reduce external inventory polling overhead (#1596)

src/functionalTest/java/appeng/test/me/storage/MEMonitorIInventoryFunctionalTest.java

@@ -0,0 +1,51 @@
+package appeng.test.me.storage;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import net.minecraft.item.Item;
+import net.minecraft.item.ItemStack;
+
+import org.junit.jupiter.api.Test;
+
+import appeng.api.config.StorageFilter;
+import appeng.api.storage.data.IAEItemStack;
+import appeng.me.storage.MEMonitorIInventory;
+import appeng.util.inv.AdaptorList;
+
+public class MEMonitorIInventoryFunctionalTest {
+
+    @Test
+    public void boundsRetainedTypesWithoutReadingTheCache() {
+        final int slots = 54;
+        final Item item = new Item().setHasSubtypes(true);
+        final List<ItemStack> contents = new ArrayList<>();
+        for (int slot = 0; slot < slots; slot++) {
+            contents.add(null);
+        }
+        final MEMonitorIInventory monitor = new MEMonitorIInventory(new AdaptorList(contents));
+        monitor.setMode(StorageFilter.NONE);
+
+        for (int poll = 0; poll < 512; poll++) {
+            for (int slot = 0; slot < slots; slot++) {
+                contents.set(slot, new ItemStack(item, 1, poll * slots + slot));
+            }
+            monitor.onTick();
+            // size() does not iterate or clean the list; iteration would hide the regression.
+            assertTrue(monitor.getStorageList().size() <= 2 * slots);
+        }
+
+        long total = 0;
+        for (final IAEItemStack stack : monitor.getStorageList()) {
+            total += stack.getStackSize();
+        }
+        assertEquals(slots, total);
+
+        contents.clear();
+        monitor.onTick();
+        assertTrue(monitor.getStorageList().isEmpty());
+    }
+}

src/main/java/appeng/me/storage/MEMonitorIInventory.java

@@ -40,6 +40,8 @@ import appeng.util.item.ItemFilterList;
 
 public class MEMonitorIInventory implements IStorageBusMonitor<IAEItemStack> {
 
+    private static final int CACHE_REFRESH_INTERVAL = 256;
+
     private final InventoryAdaptor adaptor;
     private final IItemList<IAEItemStack> list = AEApi.instance().storage().createItemList();
     private final HashMap<IMEMonitorHandlerReceiver, Object> listeners = new HashMap<>();
@@ -47,6 +49,7 @@ public class MEMonitorIInventory implements IStorageBusMonitor<IAEItemStack> {
     private BaseActionSource mySource;
     private StorageFilter mode = StorageFilter.EXTRACTABLE_ONLY;
     private boolean init = false;
+    private int ticksSinceCacheRefresh = 0;
 
     public MEMonitorIInventory(final InventoryAdaptor adaptor) {
         this.adaptor = adaptor;
@@ -123,10 +126,11 @@ public class MEMonitorIInventory implements IStorageBusMonitor<IAEItemStack> {
 
         final LinkedList<IAEStack<?>> changes = new LinkedList<>();
 
-        this.list.resetStatus();
-        int high = 0;
+        int high = -1;
+        int slots = 0;
         boolean changed = false;
         for (final ItemSlot is : this.adaptor) {
+            slots++;
             final CachedItemStack old = this.memory.get(is.getSlot());
             high = Math.max(high, is.getSlot());
 
@@ -145,7 +149,6 @@ public class MEMonitorIInventory implements IStorageBusMonitor<IAEItemStack> {
 
                 if (cis.aeStack != null) {
                     changes.add(cis.aeStack);
-                    this.list.add(cis.aeStack);
                 }
 
                 changed = true;
@@ -153,19 +156,11 @@ public class MEMonitorIInventory implements IStorageBusMonitor<IAEItemStack> {
                 final int newSize = (newIS == null ? 0 : newIS.stackSize);
                 final int diff = newSize - (oldIS == null ? 0 : oldIS.stackSize);
 
-                final IAEItemStack stack = (old == null || old.aeStack == null
-                        ? AEApi.instance().storage().createItemStack(newIS)
-                        : old.aeStack.copy());
-                if (stack != null) {
-                    stack.setStackSize(newSize);
-                    this.list.add(stack);
-                }
-
-                if (diff != 0 && stack != null) {
+                if (diff != 0 && old != null && old.aeStack != null) {
                     final CachedItemStack cis = new CachedItemStack(is.getItemStack());
                     this.memory.put(is.getSlot(), cis);
 
-                    final IAEItemStack a = stack.copy();
+                    final IAEItemStack a = old.aeStack.copy();
                     a.setStackSize(diff);
                     changes.add(a);
                     changed = true;
@@ -187,6 +182,19 @@ public class MEMonitorIInventory implements IStorageBusMonitor<IAEItemStack> {
             end.clear();
         }
 
+        // Bound zero-count entries under item-type churn without scanning the list on every poll.
+        if (++this.ticksSinceCacheRefresh >= CACHE_REFRESH_INTERVAL || this.list.size() > slots) {
+            this.list.resetStatus();
+            for (final CachedItemStack cached : this.memory.values()) {
+                this.list.add(cached.aeStack);
+            }
+            this.ticksSinceCacheRefresh = 0;
+        } else {
+            for (final IAEStack<?> change : changes) {
+                this.list.add((IAEItemStack) change);
+            }
+        }
+
         if (!changes.isEmpty()) {
             this.postDifference(changes);
         }