Prevent compression from blocking the thread too much

src/main/java/net/minestom/server/network/netty/codec/PacketCompressor.java

@@ -43,7 +43,7 @@ public class PacketCompressor extends ByteToMessageCodec<ByteBuf> {
 
     @Override
     protected void encode(ChannelHandlerContext ctx, ByteBuf from, ByteBuf to) {
-        PacketUtils.compressBuffer(deflater, buffer, from, to);
+        PacketUtils.compressBuffer(deflater, buffer, from, to, false);
     }
 
     @Override
@@ -68,13 +68,11 @@ public class PacketCompressor extends ByteToMessageCodec<ByteBuf> {
                 buf.readBytes(input);
 
                 inflater.setInput(input);
-
                 byte[] output = new byte[i];
-
                 inflater.inflate(output);
-                out.add(Unpooled.wrappedBuffer(output));
-
                 inflater.reset();
+
+                out.add(Unpooled.wrappedBuffer(output));
             }
         }
     }

src/main/java/net/minestom/server/utils/PacketUtils.java

@@ -16,6 +16,9 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.ThreadLocalRandom;
 import java.util.zip.Deflater;
 
 /**
@@ -26,8 +29,14 @@ public final class PacketUtils {
 
     private static final PacketListenerManager PACKET_LISTENER_MANAGER = MinecraftServer.getPacketListenerManager();
 
-    private final static Deflater deflater = new Deflater(3);
+    private static final int DEFLATER_COUNT = 10;
-    private final static byte[] buffer = new byte[8192];
+    private static final List<Deflater> DEFLATERS = new CopyOnWriteArrayList<>();
+
+    static {
+        for (int i = 0; i < DEFLATER_COUNT; i++) {
+            DEFLATERS.add(new Deflater(3));
+        }
+    }
 
     private PacketUtils() {
 
@@ -191,28 +200,47 @@ public final class PacketUtils {
      * {@code packetBuffer} needs to be the packet content without any header (if you want to use it to write a Minecraft packet).
      *
      * @param deflater          the deflater for zlib compression
-     * @param buffer            a cached buffer which will be used to store temporary the deflater output
+     * @param buffer            a cached buffer which will be used to store temporary the deflater output,
+     *                          null if you prefer the buffer to be allocated dynamically when required
      * @param packetBuffer      the buffer containing all the packet fields
      * @param compressionTarget the buffer which will receive the compressed version of {@code packetBuffer}
      */
-    public static void compressBuffer(@NotNull Deflater deflater, @NotNull byte[] buffer, @NotNull ByteBuf packetBuffer, @NotNull ByteBuf compressionTarget) {
+    public static void compressBuffer(@NotNull Deflater deflater, @Nullable byte[] buffer,
+                                      @NotNull ByteBuf packetBuffer, @NotNull ByteBuf compressionTarget,
+                                      boolean synchronization) {
         final int packetLength = packetBuffer.readableBytes();
 
         if (packetLength < MinecraftServer.getCompressionThreshold()) {
             Utils.writeVarIntBuf(compressionTarget, 0);
             compressionTarget.writeBytes(packetBuffer);
         } else {
+
             Utils.writeVarIntBuf(compressionTarget, packetLength);
 
-            deflater.setInput(packetBuffer.nioBuffer());
+            final Runnable compressor = () -> {
-            deflater.finish();
+                // Allocate buffer if not already
+                byte[] output = buffer != null ? buffer : new byte[8192];
 
-            while (!deflater.finished()) {
+                deflater.setInput(packetBuffer.nioBuffer());
-                final int length = deflater.deflate(buffer);
+                deflater.finish();
-                compressionTarget.writeBytes(buffer, 0, length);
+
+                while (!deflater.finished()) {
+                    final int length = deflater.deflate(output);
+                    compressionTarget.writeBytes(output, 0, length);
+                }
+
+                deflater.reset();
+                ;
+            };
+
+            // Synchronize only if asked
+            if (synchronization) {
+                synchronized (deflater) {
+                    compressor.run();
+                }
+            } else {
+                compressor.run();
             }
-
-            deflater.reset();
         }
     }
 
@@ -231,12 +259,13 @@ public final class PacketUtils {
         ByteBuf packetBuf = writePacket(serverPacket);
 
         if (MinecraftServer.getCompressionThreshold() > 0) {
-
             ByteBuf compressedBuf = directBuffer ? BufUtils.getBuffer(true) : Unpooled.buffer();
             ByteBuf framedBuf = directBuffer ? BufUtils.getBuffer(true) : Unpooled.buffer();
-            synchronized (deflater) {
+
-                compressBuffer(deflater, buffer, packetBuf, compressedBuf);
+            // Get a random deflater
-            }
+            final Deflater deflater = DEFLATERS.get(ThreadLocalRandom.current().nextInt(DEFLATER_COUNT));
+            compressBuffer(deflater, null, packetBuf, compressedBuf, true);
+
             packetBuf.release();
 
             frameBuffer(compressedBuf, framedBuf);