Fix variable & function thread safety

src/main/java/ch/njol/skript/lang/Variable.java

@@ -69,7 +69,7 @@ public class Variable<T> implements Expression<T>, KeyReceiverExpression<T>, Key
 	private final boolean list;
 
 	private final @Nullable Variable<?> source;
-	private final Map<Event, String[]> cache = new WeakHashMap<>();
+	private final Map<Event, String[]> cache = Collections.synchronizedMap(new WeakHashMap<>());
 
 	@SuppressWarnings("unchecked")
 	private Variable(VariableString name, Class<? extends T>[] types, boolean local, boolean ephemeral, boolean list, @Nullable Variable<?> source) {

src/main/java/ch/njol/skript/lang/function/ExprFunctionCall.java

@@ -23,7 +23,7 @@ public class ExprFunctionCall<T> extends SimpleExpression<T> implements KeyProvi
 	private final FunctionReference<?> function;
 	private final Class<? extends T>[] returnTypes;
 	private final Class<T> returnType;
-	private final Map<Event, String[]> cache = new WeakHashMap<>();
+	private final Map<Event, String[]> cache = Collections.synchronizedMap(new WeakHashMap<>());
 
 	public ExprFunctionCall(FunctionReference<T> function) {
 		this(function, function.returnTypes);

src/main/java/ch/njol/skript/lang/function/ScriptFunction.java

@@ -19,9 +19,9 @@ public class ScriptFunction<T> extends Function<T> implements ReturnHandler<T> {
 
 	private final Trigger trigger;
 
-	private boolean returnValueSet;
-	private T @Nullable [] returnValues;
-	private String @Nullable [] returnKeys;
+	private final ThreadLocal<Boolean> returnValueSet = ThreadLocal.withInitial(() -> false);
+	private final ThreadLocal<T @Nullable []> returnValues = new ThreadLocal<>();
+	private final ThreadLocal<String @Nullable []> returnKeys = new ThreadLocal<>();
 
 	/**
 	 * @deprecated use {@link ScriptFunction#ScriptFunction(Signature, SectionNode)} instead.
@@ -85,12 +85,12 @@ public ScriptFunction(Signature<T> sign, SectionNode node) {
 
 		trigger.execute(event);
 		ClassInfo<T> returnType = getReturnType();
-		return returnType != null ? returnValues : null;
+		return returnType != null ? returnValues.get() : null;
 	}
 
 	@Override
 	public @NotNull String @Nullable [] returnedKeys() {
-		return returnKeys;
+		return returnKeys.get();
 	}
 
 	/**
@@ -99,26 +99,26 @@ public ScriptFunction(Signature<T> sign, SectionNode node) {
 	@Deprecated(since = "2.9.0", forRemoval = true)
 	@ApiStatus.Internal
 	public final void setReturnValue(@Nullable T[] values) {
-		assert !returnValueSet;
-		returnValueSet = true;
-		this.returnValues = values;
+		assert !returnValueSet.get();
+		returnValueSet.set(true);
+		this.returnValues.set(values);
 	}
 
 	@Override
 	public boolean resetReturnValue() {
-		returnValueSet = false;
-		returnValues = null;
-		returnKeys = null;
+		returnValueSet.remove();
+		returnValues.remove();
+		returnKeys.remove();
 		return true;
 	}
 
 	@Override
 	public final void returnValues(Event event, Expression<? extends T> value) {
-		assert !returnValueSet;
-		returnValueSet = true;
-		this.returnValues = value.getArray(event);
+		assert !returnValueSet.get();
+		returnValueSet.set(true);
+		this.returnValues.set(value.getArray(event));
 		if (KeyProviderExpression.canReturnKeys(value))
-			this.returnKeys = ((KeyProviderExpression<?>) value).getArrayKeys(event);
+			this.returnKeys.set(((KeyProviderExpression<?>) value).getArrayKeys(event));
 	}
 
 	@Override

src/main/java/ch/njol/skript/variables/Variables.java

@@ -457,23 +457,23 @@ public static Object getVariable(String name, @Nullable Event event, boolean loc
 
 			return map.getVariable(n);
 		} else {
-			// Prevent race conditions from returning variables with incorrect values
-			if (!changeQueue.isEmpty()) {
-				// Gets the last VariableChange made
-				VariableChange variableChange = changeQueue.stream()
-						.filter(change -> change.name.equals(n))
-						.reduce((first, second) -> second)
-								// Gets last value, as iteration is from head to tail,
-								//  and adding occurs at the tail (and we want the most recently added)
-						.orElse(null);
-
-				if (variableChange != null) {
-					return variableChange.value;
-				}
-			}
-
 			try {
 				variablesLock.readLock().lock();
+				// Prevent race conditions from returning variables with incorrect values
+				if (!changeQueue.isEmpty()) {
+					// Gets the last VariableChange made
+					VariableChange variableChange = changeQueue.stream()
+							.filter(change -> change.name.equals(n))
+							.reduce((first, second) -> second)
+									// Gets last value, as iteration is from head to tail,
+									//  and adding occurs at the tail (and we want the most recently added)
+							.orElse(null);
+
+					if (variableChange != null) {
+						return variableChange.value;
+					}
+				}
+
 				return variables.getVariable(n);
 			} finally {
 				variablesLock.readLock().unlock();