LibJS: Implement Atomics.isLockFree

Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp

@@ -122,6 +122,7 @@ void AtomicsObject::initialize(GlobalObject& global_object)
     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.isLockFree, is_lock_free, 1, attr);
     define_native_function(vm.names.load, load, 2, attr);
     define_native_function(vm.names.or_, or_, 3, attr);
     define_native_function(vm.names.store, store, 3, attr);
@@ -262,6 +263,24 @@ JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::exchange)
     VERIFY_NOT_REACHED();
 }
 
+// 25.4.7 Atomics.isLockFree ( size ), https://tc39.es/ecma262/#sec-atomics.islockfree
+JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::is_lock_free)
+{
+    auto size = vm.argument(0).to_integer_or_infinity(global_object);
+    if (vm.exception())
+        return {};
+
+    if (size == 1)
+        return Value(AK::atomic_is_lock_free<u8>());
+    if (size == 2)
+        return Value(AK::atomic_is_lock_free<u16>());
+    if (size == 4)
+        return Value(true);
+    if (size == 8)
+        return Value(AK::atomic_is_lock_free<u64>());
+    return Value(false);
+}
+
 // 25.4.8 Atomics.load ( typedArray, index ), https://tc39.es/ecma262/#sec-atomics.load
 JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::load)
 {

Userland/Libraries/LibJS/Runtime/AtomicsObject.h

@@ -23,6 +23,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(and_);
     JS_DECLARE_NATIVE_FUNCTION(compare_exchange);
     JS_DECLARE_NATIVE_FUNCTION(exchange);
+    JS_DECLARE_NATIVE_FUNCTION(is_lock_free);
     JS_DECLARE_NATIVE_FUNCTION(load);
     JS_DECLARE_NATIVE_FUNCTION(or_);
     JS_DECLARE_NATIVE_FUNCTION(store);

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -213,6 +213,7 @@ namespace JS {
     P(isFinite)                              \
     P(isFrozen)                              \
     P(isInteger)                             \
+    P(isLockFree)                            \
     P(isNaN)                                 \
     P(isPrototypeOf)                         \
     P(isSafeInteger)                         \

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

@@ -0,0 +1,25 @@
+test("invariants", () => {
+    expect(Atomics.isLockFree).toHaveLength(1);
+});
+
+test("basic functionality", () => {
+    expect(Atomics.isLockFree(4)).toBeTrue();
+
+    // Can't assume the return value of sizes 1, 2, and 8, but they shouldn't change.
+    expect(Atomics.isLockFree(1)).toBe(Atomics.isLockFree(1));
+    expect(Atomics.isLockFree(2)).toBe(Atomics.isLockFree(2));
+    expect(Atomics.isLockFree(8)).toBe(Atomics.isLockFree(8));
+
+    expect(Atomics.isLockFree(0)).toBeFalse();
+    expect(Atomics.isLockFree(3)).toBeFalse();
+    expect(Atomics.isLockFree(5)).toBeFalse();
+    expect(Atomics.isLockFree(6)).toBeFalse();
+    expect(Atomics.isLockFree(7)).toBeFalse();
+    expect(Atomics.isLockFree(9)).toBeFalse();
+    expect(Atomics.isLockFree(10)).toBeFalse();
+    expect(Atomics.isLockFree(Infinity)).toBeFalse();
+
+    expect(Atomics.isLockFree("not a number")).toBeFalse();
+    expect(Atomics.isLockFree(new Float32Array(4))).toBeFalse();
+    expect(Atomics.isLockFree(String.prototype)).toBeFalse();
+});