Remove useless synchronization blocks and fix Inventory#addItemStack

src/main/java/net/minestom/server/instance/Chunk.java

@@ -223,12 +223,11 @@ public class Chunk implements Viewable {
         return blocksData.get(index);
     }
 
-    public void updateBlocks(long time, Instance instance) {
+    public synchronized void updateBlocks(long time, Instance instance) {
         if (updatableBlocks.isEmpty())
             return;
 
         // Block all chunk operation during the update
-        synchronized (this) {
         IntIterator iterator = new IntOpenHashSet(updatableBlocks).iterator();
         while (iterator.hasNext()) {
             int index = iterator.nextInt();
@@ -253,7 +252,6 @@ public class Chunk implements Viewable {
             customBlock.update(instance, blockPosition, data);
         }
     }
-    }
 
     public Biome[] getBiomes() {
         return biomes;

src/main/java/net/minestom/server/instance/batch/BlockBatch.java

@@ -21,29 +21,23 @@ public class BlockBatch implements InstanceBatch {
     }
 
     @Override
-    public void setBlock(int x, int y, int z, short blockId, Data data) {
-        synchronized (this) {
+    public synchronized void setBlock(int x, int y, int z, short blockId, Data data) {
         Chunk chunk = this.instance.getChunkAt(x, z);
         addBlockData(chunk, x, y, z, false, blockId, (short) 0, data);
     }
-    }
 
     @Override
-    public void setCustomBlock(int x, int y, int z, short blockId, Data data) {
-        synchronized (this) {
+    public synchronized void setCustomBlock(int x, int y, int z, short blockId, Data data) {
         Chunk chunk = this.instance.getChunkAt(x, z);
         CustomBlock customBlock = BLOCK_MANAGER.getCustomBlock(blockId);
         addBlockData(chunk, x, y, z, true, customBlock.getBlockId(), blockId, data);
     }
-    }
 
     @Override
-    public void setSeparateBlocks(int x, int y, int z, short blockId, short customBlockId, Data data) {
-        synchronized (this) {
+    public synchronized void setSeparateBlocks(int x, int y, int z, short blockId, short customBlockId, Data data) {
         Chunk chunk = this.instance.getChunkAt(x, z);
         addBlockData(chunk, x, y, z, true, blockId, customBlockId, data);
     }
-    }
 
     private void addBlockData(Chunk chunk, int x, int y, int z, boolean customBlock, short blockId, short customBlockId, Data data) {
         List<BlockData> blocksData = this.data.get(chunk);

src/main/java/net/minestom/server/inventory/Inventory.java

@@ -8,6 +8,7 @@ import net.minestom.server.inventory.click.InventoryClickProcessor;
 import net.minestom.server.inventory.click.InventoryClickResult;
 import net.minestom.server.inventory.condition.InventoryCondition;
 import net.minestom.server.item.ItemStack;
+import net.minestom.server.item.StackingRule;
 import net.minestom.server.network.PacketWriterUtils;
 import net.minestom.server.network.packet.server.play.SetSlotPacket;
 import net.minestom.server.network.packet.server.play.WindowItemsPacket;
@@ -88,7 +89,32 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
     }
 
     @Override
-    public boolean addItemStack(ItemStack itemStack) {
+    public synchronized boolean addItemStack(ItemStack itemStack) {
+        StackingRule stackingRule = itemStack.getStackingRule();
+        for (int i = 0; i < getItemStacks().length; i++) {
+            ItemStack item = getItemStacks()[i];
+            StackingRule itemStackingRule = item.getStackingRule();
+            if (itemStackingRule.canBeStacked(itemStack, item)) {
+                int itemAmount = itemStackingRule.getAmount(item);
+                if (itemAmount == stackingRule.getMaxSize())
+                    continue;
+                int itemStackAmount = itemStackingRule.getAmount(itemStack);
+                int totalAmount = itemStackAmount + itemAmount;
+                if (!stackingRule.canApply(itemStack, totalAmount)) {
+                    item = itemStackingRule.apply(item, itemStackingRule.getMaxSize());
+
+                    sendSlotRefresh((short) i, item);
+                    itemStack = stackingRule.apply(itemStack, totalAmount - stackingRule.getMaxSize());
+                } else {
+                    item.setAmount((byte) totalAmount);
+                    sendSlotRefresh((short) i, item);
+                    return true;
+                }
+            } else if (item.isAir()) {
+                setItemStack(i, itemStack);
+                return true;
+            }
+        }
         return false;
     }
 
@@ -161,8 +187,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
         return cursorPlayersItem.getOrDefault(player, ItemStack.getAirItem());
     }
 
-    private void safeItemInsert(int slot, ItemStack itemStack) {
-        synchronized (this) {
+    private synchronized void safeItemInsert(int slot, ItemStack itemStack) {
         itemStack = ItemStackUtils.notNull(itemStack);
         this.itemStacks[slot] = itemStack;
         SetSlotPacket setSlotPacket = new SetSlotPacket();
@@ -171,7 +196,6 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
         setSlotPacket.itemStack = itemStack;
         sendPacketToViewers(setSlotPacket);
     }
-    }
 
     private WindowItemsPacket createWindowItemsPacket() {
         WindowItemsPacket windowItemsPacket = new WindowItemsPacket();
@@ -440,6 +464,14 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
         return !clickResult.isCancel();
     }
 
+    private void sendSlotRefresh(short slot, ItemStack itemStack) {
+        SetSlotPacket setSlotPacket = new SetSlotPacket();
+        setSlotPacket.windowId = getWindowId();
+        setSlotPacket.slot = slot;
+        setSlotPacket.itemStack = itemStack;
+        sendPacketToViewers(setSlotPacket);
+    }
+
     /**
      * Used to update the inventory for a specific player in order to fix his cancelled actions
      *

src/main/java/net/minestom/server/inventory/PlayerInventory.java

@@ -72,8 +72,7 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
     }
 
     @Override
-    public boolean addItemStack(ItemStack itemStack) {
-        synchronized (this) {
+    public synchronized boolean addItemStack(ItemStack itemStack) {
         StackingRule stackingRule = itemStack.getStackingRule();
         for (int i = 0; i < items.length - 10; i++) {
             ItemStack item = items[i];
@@ -99,7 +98,6 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
                 return true;
             }
         }
-        }
         return false;
     }
 
@@ -184,8 +182,7 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
         this.cursorItem = ItemStackUtils.notNull(cursorItem);
     }
 
-    private void safeItemInsert(int slot, ItemStack itemStack) {
-        synchronized (this) {
+    private synchronized void safeItemInsert(int slot, ItemStack itemStack) {
         itemStack = ItemStackUtils.notNull(itemStack);
 
         EntityEquipmentPacket.Slot equipmentSlot;
@@ -228,7 +225,6 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
         update();
         //refreshSlot(slot); seems to break things concerning +64 stacks
     }
-    }
 
     protected void setItemStack(int slot, int offset, ItemStack itemStack) {
         slot = convertSlot(slot, offset);

src/main/java/net/minestom/server/network/player/FakePlayerConnection.java

@@ -29,7 +29,7 @@ public class FakePlayerConnection extends PlayerConnection {
 
     @Override
     public void flush() {
-        throw new UnsupportedOperationException("FakePlayer does not have anything to flush");
+        // Does nothing
     }
 
     @Override