resolve packet instance construction concurrency issue (#2312)

Author: derklaro

src/main/java/com/comphenix/protocol/injector/StructureCache.java

@@ -54,7 +54,9 @@ public class StructureCache {
 	private static final Map<PacketType, StructureModifier<Object>> STRUCTURE_MODIFIER_CACHE = new ConcurrentHashMap<>();
 
 	// packet data serializer which always returns an empty nbt tag compound
+	private static final Object TRICK_INIT_LOCK = new Object();
 	private static boolean TRICK_TRIED = false;
+
 	private static ConstructorAccessor TRICKED_DATA_SERIALIZER_BASE;
 	private static ConstructorAccessor TRICKED_DATA_SERIALIZER_JSON;
 
@@ -164,45 +166,50 @@ public static boolean tryInitTrickDataSerializer() {
 			return TRICKED_DATA_SERIALIZER_BASE != null;
 		}
 
-		// prevent double init
-		TRICK_TRIED = true;
-
-		try {
-			// create an empty instance of a nbt tag compound / text compound that we can re-use when needed
-			Object textCompound = WrappedChatComponent.fromText("").getHandle();
-			Object compound = Accessors.getConstructorAccessor(MinecraftReflection.getNBTCompoundClass()).invoke();
-			// base builder which intercepts a few methods
-			DynamicType.Builder<?> baseBuilder = ByteBuddyFactory.getInstance()
-					.createSubclass(MinecraftReflection.getPacketDataSerializerClass())
-					.name(MinecraftMethods.class.getPackage().getName() + ".ProtocolLibTricksNmsDataSerializerBase")
-					.method(ElementMatchers.returns(MinecraftReflection.getNBTCompoundClass())
-							.and(ElementMatchers.takesArguments(MinecraftReflection.getNBTReadLimiterClass())))
-					.intercept(FixedValue.value(compound))
-					.method(ElementMatchers.returns(MinecraftReflection.getIChatBaseComponentClass()))
-					.intercept(FixedValue.value(textCompound))
-					.method(ElementMatchers.returns(PublicKey.class).and(ElementMatchers.takesNoArguments()))
-					.intercept(FixedValue.nullValue());
-			Class<?> serializerBase = baseBuilder.make()
-					.load(ByteBuddyFactory.getInstance().getClassLoader(), Default.INJECTION)
-					.getLoaded();
-			TRICKED_DATA_SERIALIZER_BASE = Accessors.getConstructorAccessor(serializerBase, ByteBuf.class);
-
-			// extended builder which intercepts the read string method as well
-			Class<?> withStringIntercept = baseBuilder
-					.name(MinecraftMethods.class.getPackage().getName() + ".ProtocolLibTricksNmsDataSerializerJson")
-					.method(ElementMatchers.returns(String.class).and(ElementMatchers.takesArguments(int.class)))
-					.intercept(FixedValue.value("{}"))
-					.make()
-					.load(ByteBuddyFactory.getInstance().getClassLoader(), Default.INJECTION)
-					.getLoaded();
-			TRICKED_DATA_SERIALIZER_JSON = Accessors.getConstructorAccessor(withStringIntercept, ByteBuf.class);
-
-			// worked
-			return true;
-		} catch (Exception ignored) {
-		}
+		synchronized (TRICK_INIT_LOCK) {
+			if (TRICK_TRIED) {
+				return TRICKED_DATA_SERIALIZER_BASE != null;
+			}
 
-		// didn't work
-		return false;
+			try {
+				// create an empty instance of a nbt tag compound / text compound that we can re-use when needed
+				Object textCompound = WrappedChatComponent.fromText("").getHandle();
+				Object compound = Accessors.getConstructorAccessor(MinecraftReflection.getNBTCompoundClass()).invoke();
+				// base builder which intercepts a few methods
+				DynamicType.Builder<?> baseBuilder = ByteBuddyFactory.getInstance()
+						.createSubclass(MinecraftReflection.getPacketDataSerializerClass())
+						.name(MinecraftMethods.class.getPackage().getName() + ".ProtocolLibTricksNmsDataSerializerBase")
+						.method(ElementMatchers.returns(MinecraftReflection.getNBTCompoundClass())
+								.and(ElementMatchers.takesArguments(MinecraftReflection.getNBTReadLimiterClass())))
+						.intercept(FixedValue.value(compound))
+						.method(ElementMatchers.returns(MinecraftReflection.getIChatBaseComponentClass()))
+						.intercept(FixedValue.value(textCompound))
+						.method(ElementMatchers.returns(PublicKey.class).and(ElementMatchers.takesNoArguments()))
+						.intercept(FixedValue.nullValue());
+				Class<?> serializerBase = baseBuilder.make()
+						.load(ByteBuddyFactory.getInstance().getClassLoader(), Default.INJECTION)
+						.getLoaded();
+				TRICKED_DATA_SERIALIZER_BASE = Accessors.getConstructorAccessor(serializerBase, ByteBuf.class);
+
+				// extended builder which intercepts the read string method as well
+				Class<?> withStringIntercept = baseBuilder
+						.name(MinecraftMethods.class.getPackage().getName() + ".ProtocolLibTricksNmsDataSerializerJson")
+						.method(ElementMatchers.returns(String.class).and(ElementMatchers.takesArguments(int.class)))
+						.intercept(FixedValue.value("{}"))
+						.make()
+						.load(ByteBuddyFactory.getInstance().getClassLoader(), Default.INJECTION)
+						.getLoaded();
+				TRICKED_DATA_SERIALIZER_JSON = Accessors.getConstructorAccessor(withStringIntercept, ByteBuf.class);
+
+				// worked
+				return true;
+			} catch (Exception ignored) {
+			} finally {
+				TRICK_TRIED = true;
+			}
+
+			// didn't work
+			return false;
+		}
 	}
 }