LibJS: Implement Atomics.compareExchange

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/33eb8309297
Pull-request: https://github.com/SerenityOS/serenity/pull/8752
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/Atomic.h>
 #include <AK/ByteBuffer.h>
+#include <AK/Endian.h>
 #include <LibJS/Runtime/AtomicsObject.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/TypedArray.h>
@@ -119,6 +120,7 @@ void AtomicsObject::initialize(GlobalObject& global_object)
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.add, add, 3, attr);
     define_native_function(vm.names.and_, and_, 3, attr);
+    define_native_function(vm.names.compareExchange, compare_exchange, 4, attr);
     define_native_function(vm.names.exchange, exchange, 3, attr);
     define_native_function(vm.names.load, load, 2, attr);
     define_native_function(vm.names.or_, or_, 3, attr);
@@ -166,6 +168,82 @@ JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::and_)
     VERIFY_NOT_REACHED();
 }
 
+template<typename T>
+static Value atomic_compare_exchange_impl(GlobalObject& global_object, TypedArrayBase& typed_array)
+{
+    auto& vm = global_object.vm();
+
+    validate_integer_typed_array(global_object, typed_array);
+    if (vm.exception())
+        return {};
+
+    auto indexed_position = validate_atomic_access(global_object, typed_array, vm.argument(1));
+    if (!indexed_position.has_value())
+        return {};
+
+    Value expected;
+    Value replacement;
+    if (typed_array.content_type() == TypedArrayBase::ContentType::BigInt) {
+        expected = vm.argument(2).to_bigint(global_object);
+        if (vm.exception())
+            return {};
+        replacement = vm.argument(3).to_bigint(global_object);
+        if (vm.exception())
+            return {};
+    } else {
+        expected = Value(vm.argument(2).to_integer_or_infinity(global_object));
+        if (vm.exception())
+            return {};
+        replacement = Value(vm.argument(3).to_integer_or_infinity(global_object));
+        if (vm.exception())
+            return {};
+    }
+
+    if (typed_array.viewed_array_buffer()->is_detached()) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::DetachedArrayBuffer);
+        return {};
+    }
+
+    constexpr bool is_little_endian = __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__;
+
+    auto& block = typed_array.viewed_array_buffer()->buffer();
+    auto expected_bytes = numeric_to_raw_bytes<T>(global_object, expected, is_little_endian);
+    auto replacement_bytes = numeric_to_raw_bytes<T>(global_object, replacement, is_little_endian);
+
+    // FIXME: Implement SharedArrayBuffer case.
+
+    auto raw_bytes_read = block.slice(*indexed_position, sizeof(T));
+
+    if constexpr (IsFloatingPoint<T>) {
+        VERIFY_NOT_REACHED();
+    } else {
+        using U = Conditional<IsSame<ClampedU8, T>, u8, T>;
+
+        auto* v = reinterpret_cast<U*>(block.span().slice(*indexed_position).data());
+        auto* e = reinterpret_cast<U*>(expected_bytes.data());
+        auto* r = reinterpret_cast<U*>(replacement_bytes.data());
+        (void)AK::atomic_compare_exchange_strong(v, *e, *r);
+    }
+
+    return raw_bytes_to_numeric<T>(global_object, raw_bytes_read, is_little_endian);
+}
+
+// 25.4.5 Atomics.compareExchange ( typedArray, index, expectedValue, replacementValue ), https://tc39.es/ecma262/#sec-atomics.compareexchange
+JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::compare_exchange)
+{
+    auto* typed_array = typed_array_from(global_object, vm.argument(0));
+    if (!typed_array)
+        return {};
+
+#define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, Type) \
+    if (is<ClassName>(typed_array))                                                 \
+        return atomic_compare_exchange_impl<Type>(global_object, *typed_array);
+    JS_ENUMERATE_TYPED_ARRAYS
+#undef __JS_ENUMERATE
+
+    VERIFY_NOT_REACHED();
+}
+
 // 25.4.6 Atomics.exchange ( typedArray, index, value ), https://tc39.es/ecma262/#sec-atomics.exchange
 JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::exchange)
 {

Userland/Libraries/LibJS/Runtime/AtomicsObject.h

@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(add);
     JS_DECLARE_NATIVE_FUNCTION(and_);
+    JS_DECLARE_NATIVE_FUNCTION(compare_exchange);
     JS_DECLARE_NATIVE_FUNCTION(exchange);
     JS_DECLARE_NATIVE_FUNCTION(load);
     JS_DECLARE_NATIVE_FUNCTION(or_);

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -88,6 +88,7 @@ namespace JS {
     P(clear)                                 \
     P(clz32)                                 \
     P(codePointAt)                           \
+    P(compareExchange)                       \
     P(concat)                                \
     P(configurable)                          \
     P(console)                               \

Userland/Libraries/LibJS/Tests/builtins/Atomics/Atomics.compareExchange.js

@@ -0,0 +1,64 @@
+test("invariants", () => {
+    expect(Atomics.compareExchange).toHaveLength(4);
+});
+
+test("error cases", () => {
+    expect(() => {
+        Atomics.compareExchange("not an array", 0, 0, 0);
+    }).toThrow(TypeError);
+
+    expect(() => {
+        const bad_array_type = new Float32Array(4);
+        Atomics.compareExchange(bad_array_type, 0, 0, 0);
+    }).toThrow(TypeError);
+
+    expect(() => {
+        const bad_array_type = new Uint8ClampedArray(4);
+        Atomics.compareExchange(bad_array_type, 0, 0, 0);
+    }).toThrow(TypeError);
+
+    expect(() => {
+        const array = new Int32Array(4);
+        Atomics.compareExchange(array, 100, 0, 0);
+    }).toThrow(RangeError);
+});
+
+test("basic functionality (non-BigInt)", () => {
+    [Int8Array, Int16Array, Int32Array, Uint8Array, Uint16Array, Uint32Array].forEach(ArrayType => {
+        const array = new ArrayType(2);
+        array[0] = 1;
+        array[1] = 2;
+
+        expect(Atomics.compareExchange(array, 0, 0, 5)).toBe(1);
+        expect(array).toEqual([1, 2]);
+
+        expect(Atomics.compareExchange(array, 0, 1, "5")).toBe(1);
+        expect(array).toEqual([5, 2]);
+
+        expect(Atomics.compareExchange(array, 0, "5", 6)).toBe(5);
+        expect(array).toEqual([6, 2]);
+
+        expect(Atomics.compareExchange(array, 1, 2, 3.14)).toBe(2);
+        expect(array).toEqual([6, 3]);
+    });
+});
+
+test("basic functionality (BigInt)", () => {
+    [BigInt64Array, BigUint64Array].forEach(ArrayType => {
+        const array = new ArrayType(2);
+        array[0] = 1n;
+        array[1] = 2n;
+
+        expect(Atomics.compareExchange(array, 0, 0n, 5n)).toBe(1n);
+        expect(array).toEqual([1n, 2n]);
+
+        expect(Atomics.compareExchange(array, 0, 1n, 5n)).toBe(1n);
+        expect(array).toEqual([5n, 2n]);
+
+        expect(Atomics.compareExchange(array, 0, 5n, 6n)).toBe(5n);
+        expect(array).toEqual([6n, 2n]);
+
+        expect(Atomics.compareExchange(array, 1, 2n, 3n)).toBe(2n);
+        expect(array).toEqual([6n, 3n]);
+    });
+});