src/third_party/v8/src/builtins/promise-race.tq

// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include 'src/builtins/builtins-promise-gen.h'

namespace promise {

// https://tc39.es/ecma262/#sec-promise.race
transitioning javascript builtin
PromiseRace(
    js-implicit context: Context, receiver: JSAny)(iterable: JSAny): JSAny {
  const receiver = Cast<JSReceiver>(receiver)
      otherwise ThrowTypeError(MessageTemplate::kCalledOnNonObject, 'Promise.race');

  const nativeContext = LoadNativeContext(context);

  // Let promiseCapability be ? NewPromiseCapability(C).
  // Don't fire debugEvent so that forwarding the rejection through all does
  // not trigger redundant ExceptionEvents
  const capability = NewPromiseCapability(receiver, False);
  const resolve = capability.resolve;
  const reject = capability.reject;
  const promise = capability.promise;

  // NewPromiseCapability guarantees that receiver is Constructor.
  assert(Is<Constructor>(receiver));
  const constructor = UnsafeCast<Constructor>(receiver);

  // For catch prediction, don't treat the .then calls as handling it;
  // instead, recurse outwards.
  if (IsDebugActive()) deferred {
      SetPropertyStrict(context, reject, kPromiseForwardingHandlerSymbol, True);
    }

  try {
    let promiseResolveFunction: JSAny;
    let i: iterator::IteratorRecord;
    try {
      // Let promiseResolve be GetPromiseResolve(C).
      // IfAbruptRejectPromise(promiseResolve, promiseCapability).
      promiseResolveFunction = GetPromiseResolve(nativeContext, constructor);

      // Let iterator be GetIterator(iterable).
      // IfAbruptRejectPromise(iterator, promiseCapability).
      i = iterator::GetIterator(iterable);
    } catch (e) deferred {
      goto Reject(e);
    }

    // Let result be PerformPromiseRace(iteratorRecord, C, promiseCapability).
    try {
      const fastIteratorResultMap = *NativeContextSlot(
          nativeContext, ContextSlot::ITERATOR_RESULT_MAP_INDEX);
      while (true) {
        let nextValue: JSAny;
        try {
          // Let next be IteratorStep(iteratorRecord.[[Iterator]]).
          // If next is an abrupt completion, set iteratorRecord.[[Done]] to
          // true. ReturnIfAbrupt(next).
          const next: JSReceiver = iterator::IteratorStep(
              i, fastIteratorResultMap) otherwise return promise;

          // Let nextValue be IteratorValue(next).
          // If nextValue is an abrupt completion, set iteratorRecord.[[Done]]
          // to true.
          // ReturnIfAbrupt(nextValue).
          nextValue = iterator::IteratorValue(next, fastIteratorResultMap);
        } catch (e) {
          goto Reject(e);
        }
        // Let nextPromise be ? Call(constructor, _promiseResolve_, «
        // nextValue »).
        const nextPromise =
            CallResolve(constructor, promiseResolveFunction, nextValue);

        // Perform ? Invoke(nextPromise, "then", « resolveElement,
        //                  resultCapability.[[Reject]] »).
        const then = GetProperty(nextPromise, kThenString);
        const thenResult = Call(
            context, then, nextPromise, UnsafeCast<JSAny>(resolve),
            UnsafeCast<JSAny>(reject));

        // For catch prediction, mark that rejections here are semantically
        // handled by the combined Promise.
        if (IsDebugActive() && !Is<JSPromise>(promise)) deferred {
            SetPropertyStrict(
                context, thenResult, kPromiseHandledBySymbol, promise);
          }
      }
    } catch (e) deferred {
      iterator::IteratorCloseOnException(i);
      goto Reject(e);
    }
  } label Reject(exception: Object) deferred {
    Call(
        context, UnsafeCast<JSAny>(reject), Undefined,
        UnsafeCast<JSAny>(exception));
    return promise;
  }
  unreachable;
}
}