ivalue.cpp

#include <ATen/core/ivalue.h>
#include <ATen/core/Dict.h>
#include <ATen/core/Formatting.h>
#include <ATen/core/function.h>
#include <ATen/core/jit_type.h>
#include <c10/util/StringUtil.h>
#include <cmath>

namespace c10 {
bool _fastEqualsForContainer(const IValue& lhs, const IValue& rhs) {
  if (lhs.is(rhs)) {
    // Like Python, for containers we consider identity equality to be
    // sufficient but not necessary for value equality
    return true;
  }
  return lhs == rhs;
}

namespace ivalue {

// This is in ivalue.cpp because we need to access Type::annotation_str, which
// is declared in jit_type.h
void checkCustomClassType(TypePtr expected_type, TypePtr actual_type) {
  // NB: doing pointer comparison here
  // If in the future there ever arises a need to call operator== on custom class
  // Type's, this needs to be changed!
  TORCH_CHECK(actual_type == expected_type,
              "Tried to convert an IValue of type ",
              actual_type->repr_str(),
              " to custom class type ",
              expected_type->repr_str());
}

CAFFE2_API c10::intrusive_ptr<ConstantString> ConstantString::create(
    std::string str_) {
  return c10::make_intrusive<ConstantString>(std::move(str_));
}

bool operator==(const ivalue::Tuple& lhs, const ivalue::Tuple& rhs) {
  return lhs.elements_.size() == rhs.elements_.size() &&
      // see [container equality]
      std::equal(
             lhs.elements_.cbegin(),
             lhs.elements_.cend(),
             rhs.elements_.cbegin(),
             _fastEqualsForContainer);
}

TupleTypePtr Tuple::type() const {
  if (!type_) {
    type_ = TupleType::create(
        fmap(elements_, [&](const IValue& v) { return v.type(); }));
  }
  return type_;
}

bool operator==(const ivalue::EnumHolder& lhs, const ivalue::EnumHolder& rhs) {
  return lhs.name() == rhs.name() && *rhs.type() == *lhs.type();
}

const std::string ivalue::EnumHolder::qualifiedClassName() const {
  return type_->qualifiedClassName().qualifiedName();
}

const std::string ivalue::EnumHolder::unqualifiedClassName() const {
  return type_->qualifiedClassName().name();
}

} // namespace ivalue

TypePtr IValue::type() const {
  switch (tag) {
    case Tag::None:
      return NoneType::get();
    case Tag::Tensor:
      return TensorType::create(toTensor());
    case Tag::Double:
      return FloatType::get();
    case Tag::Int:
      return IntType::get();
    case Tag::Bool:
      return BoolType::get();
    case Tag::String:
      return StringType::get();
    case Tag::Blob:
      return AnyType::get();
    case Tag::GenericDict: {
      auto d = toGenericDict();
      return DictType::create(d.keyType(), d.valueType());
    }
    case Tag::GenericList:
      return ListType::create(toList().elementType());
    case Tag::Future:
      return FutureType::create(toFuture()->elementType());
    case Tag::RRef:
      return RRefType::create(toRRef()->type());
    case Tag::Device:
      return DeviceObjType::get();
    case Tag::Object:
      return toObjectRef().type();
    case Tag::PyObject:
      return PyObjectType::get();
    case Tag::Uninitialized:
      return AnyType::get();
    case Tag::Capsule:
      return CapsuleType::get();
    case Tag::Tuple:
      return toTuple()->type();
    case Tag::Generator:
      return GeneratorType::get();
    case Tag::Quantizer:
      return QuantizerType::get();
    case Tag::Enum:
      return toEnumHolder()->type();
  }
  // switch above is complete but this silences compiler warnings
  TORCH_INTERNAL_ASSERT(false, "unhandled case in IValue::type()");
}

void IValue::visit(const std::function<bool (const IValue &)>& visitor) const {
  if (visitor(*this)) {
    // Short cut.
    return;
  }
  switch (this->tag) {
    case Tag::Tuple:
    case Tag::GenericList: {
      c10::ArrayRef<IValue> elems;
      if (isTuple()) {
        elems = this->toTuple()->elements();
      } else {
        elems = this->toListRef();
      }
      for (auto& elem : elems) {
        elem.visit(visitor);
      }
      break;
    }
    case Tag::GenericDict:
      for (const auto& pair : this->toGenericDict()) {
        pair.value().visit(visitor);
        pair.key().visit(visitor);
      }
      break;
    case Tag::Object: {
      auto obj_type = type()->expect<ClassType>();
      auto obj_value = toObject();
      auto attributes = obj_type->getAttributes();
      for (const auto& attr: attributes) {
        auto attribute = obj_value->getAttr(attr.getName());
        attribute.visit(visitor);
      }
      break;
    }
    default:
      break;
 }
}

void IValue::getSubValues(HashAliasedIValues& subValues) const {
  switch (this->tag) {
    case Tag::Tensor:
      subValues.insert(*this);
      return;
    case Tag::Tuple:
    case Tag::GenericList: {
      subValues.insert(*this);
      c10::ArrayRef<IValue> elems;
      if (isTuple()) {
        elems = this->toTuple()->elements();
      } else {
        elems = this->toListRef();
      }
      for (auto& elem : elems) {
        elem.getSubValues(subValues);
      }
      break;
    }
    case Tag::GenericDict:
      subValues.insert(*this);
      for (const auto& pair : this->toGenericDict()) {
        pair.value().getSubValues(subValues);
        pair.key().getSubValues(subValues);
      }
      break;
    case Tag::Object: {
      // Record Object IValue and its attributes.
      subValues.insert(*this);
      auto obj_type = type()->expect<ClassType>();
      auto obj_value = toObject();
      auto attributes = obj_type->getAttributes();
      for (const auto& attr: attributes) {
        auto attribute = obj_value->getAttr(attr.getName());
        attribute.getSubValues(subValues);
      }
      break;
    }
    case Tag::Future:
    case Tag::Device:
    case Tag::PyObject:
    case Tag::Uninitialized:
    case Tag::Capsule:
      TORCH_INTERNAL_ASSERT(
          false, "sub ivalue is nat enabled for: ", this->tagKind());
      // Fall through
    default:
      // don't record scalars.
      break;
  }
}

bool IValue::overlaps(const IValue& rhs) const {
  HashAliasedIValues rhsSubValues, thisSubValues;
  rhs.getSubValues(rhsSubValues);
  getSubValues(thisSubValues);
  for (auto& sub : thisSubValues) {
    if (rhsSubValues.count(sub)) {
      return true;
    }
  }
  return false;
}

bool operator!=(const IValue& lhs, const IValue& rhs) {
  return !(lhs == rhs);
}

bool operator==(const IValue& lhs, const IValue& rhs) {
  IValue eq = lhs.equals(rhs);
  if (eq.isBool()) {
    return eq.toBool();
  }
  // The only case we don't return bool is for tensor comparison. In Python,
  // `bool()` is called on the return value of `__eq__` if the return value is
  // not a boolean. Mimic that behavior here.
  TORCH_INTERNAL_ASSERT(eq.isTensor());
  return eq.toTensor().is_nonzero();
}

bool IValue::ptrEqual(const IValue& lhs, const IValue& rhs) {
  TORCH_INTERNAL_ASSERT(lhs.is_intrusive_ptr);
  TORCH_INTERNAL_ASSERT(rhs.is_intrusive_ptr);
  return lhs.tag == rhs.tag &&
      lhs.payload.as_intrusive_ptr == rhs.payload.as_intrusive_ptr;
}

IValue IValue::equals(const IValue& rhs) const {
  const IValue& lhs = *this;
  switch (lhs.tag) {
    case Tag::None:
      // In Python you're not supposed to do this comparison apparently. Not
      // sure if we should warn here or what
      return rhs.isNone();
    case Tag::Tensor:
      if (!rhs.isTensor()) {
        return false;
      }
      return lhs.toTensor().eq(rhs.toTensor());
    case Tag::Double:
      return rhs.isDouble() && lhs.toDouble() == rhs.toDouble();
    case Tag::Int:
      return rhs.isInt() && lhs.toInt() == rhs.toInt();
    case Tag::Bool:
      return rhs.isBool() && lhs.toBool() == rhs.toBool();
    case Tag::String:
      return rhs.isString() && lhs.toStringRef() == rhs.toStringRef();
    case Tag::GenericDict:
      return rhs.isGenericDict() && lhs.toGenericDict() == rhs.toGenericDict();
    case Tag::Tuple:
      return rhs.isTuple() && *lhs.toTuple() == *rhs.toTuple();
    case Tag::Device:
      return rhs.isDevice() && lhs.toDevice() == rhs.toDevice();
    case Tag::GenericList:
      return rhs.isList() && lhs.toList() == rhs.toList();
    case Tag::Blob:
    case Tag::Future:
    case Tag::RRef:
    case Tag::Object:
    case Tag::PyObject:
    case Tag::Capsule:
    case Tag::Generator:
    case Tag::Quantizer:
      return ptrEqual(lhs, rhs);
    case Tag::Enum:
      return lhs.toEnumHolder()->is(*rhs.toEnumHolder());
    case Tag::Uninitialized:
      // Unitialized ivalues show up in no-ops when the compiler can prove a
      // value will never be used. Just return false on any equality comparison.
      return false;
  }
  // the above switch should be exhaustive
  TORCH_INTERNAL_ASSERT(false, "we should never reach here")
}

static bool isUndefinedTensor(const IValue& iv) {
  return iv.isTensor() && !iv.toTensor().defined();
}

bool IValue::is(const IValue& rhs) const {
  const IValue& lhs = *this;
  // Special handling for undefined tensors:
  // 1. Undefined_tensor is None and vice versa.
  if ((isUndefinedTensor(lhs) && rhs.isNone()) ||
      (lhs.isNone() && isUndefinedTensor(rhs))) {
    return true;
  }
  // 2. Undefined_tensor is Undefined_tensor.
  if (isUndefinedTensor(lhs) && isUndefinedTensor(rhs)) {
    return true;
  }

  if (lhs.isTensor()) {
    // Use the standard way of comparing two tensors for identity
    return rhs.isTensor() && lhs.toTensor().is_same(rhs.toTensor());
  }

  if (lhs.is_intrusive_ptr) {
    return rhs.is_intrusive_ptr && ptrEqual(lhs, rhs);
  }
  return lhs == rhs;
}

namespace {

using IValueFormatter = std::function<void(std::ostream&, const IValue&)>;

template <class T>
std::ostream& printList(
    std::ostream& out,
    const T& list,
    const std::string start,
    const std::string finish,
    IValueFormatter formatter) {
  out << start;
  for (size_t i = 0; i < list.size(); ++i) {
    if (i > 0) {
      out << ", ";
    }
    formatter(out, IValue(list[i]));
  }
  out << finish;
  return out;
}

// Properly disambiguate the type of an empty list
std::ostream& printMaybeAnnotatedList(
    std::ostream& out,
    const IValue& the_list,
    IValueFormatter formatter) {
  auto list_elem_type = the_list.type()->expect<ListType>()->getElementType();
  if (the_list.toListRef().size() == 0 ||
      !elementTypeCanBeInferredFromMembers(list_elem_type)) {
    out << "annotate(" << the_list.type()->annotation_str() << ", ";
    printList(out, the_list.toListRef(), "[", "]", formatter);
    out << ")";
    return out;
  } else {
    return printList(out, the_list.toListRef(), "[", "]", formatter);
  }
}

template <typename Dict>
std::ostream& printDict(
    std::ostream& out,
    const Dict& v,
    IValueFormatter formatter) {
  out << "{";

  bool first = true;
  for (const auto& pair : v) {
    if (!first) {
      out << ", ";
    }

    formatter(out, pair.key());
    out << ": ";
    formatter(out, pair.value());
    first = false;
  }

  out << "}";
  return out;
}
}

// Properly disambiguate the type of an empty dict
std::ostream& printMaybeAnnotatedDict(
    std::ostream& out,
    const IValue& the_dict,
    IValueFormatter formatter) {
  auto value_type = the_dict.type()->cast<DictType>()->getValueType();
  if (the_dict.toGenericDict().size() == 0 ||
      !elementTypeCanBeInferredFromMembers(value_type)) {
    out << "annotate(" << the_dict.type()->annotation_str() << ",";
    printDict(out, the_dict.toGenericDict(), formatter) << ")";
  } else {
    return printDict(out, the_dict.toGenericDict(), formatter);
  }
  return out;
}

std::ostream& IValue::repr(
    std::ostream& out,
    std::function<bool(std::ostream&, const IValue& v)>
        customFormatter) const {
  // First check if the caller has provided a custom formatter. Use that if possible.
  if (customFormatter(out, *this)) {
    return out;
  }

  const IValue& v = *this;
  // continue to use custom formatter in recursion
  auto formatter = [&](std::ostream& out, const IValue& input) {
    input.repr(out, customFormatter);
  };
  switch (v.tag) {
    case IValue::Tag::None:
      return out << v.toNone();
    case IValue::Tag::Double: {
      double d = v.toDouble();
      int c = std::fpclassify(d);
      if ((c == FP_NORMAL || c == FP_ZERO ) && std::abs(d) < 1e10) {
        int64_t i = int64_t(d);
        if (double(i) == d) {
          return out << i << ".";
        }
      }
      auto orig_prec = out.precision();
      return out << std::setprecision(std::numeric_limits<double>::max_digits10)
                 << v.toDouble() << std::setprecision(orig_prec);
    }
    case IValue::Tag::Int:
      return out << v.toInt();
    case IValue::Tag::Bool:
      return out << (v.toBool() ? "True" : "False");
    case IValue::Tag::Tuple: {
      const auto& elements = v.toTuple()->elements();
      const auto& finish = elements.size() == 1 ? ",)" : ")";
      return printList(out, elements, "(", finish, formatter);
    }
    case IValue::Tag::String:
      c10::printQuotedString(out, v.toStringRef());
      return out;
    case IValue::Tag::GenericList: {
      return printMaybeAnnotatedList(out, *this, formatter);
    }
    case IValue::Tag::Device: {
      std::stringstream device_stream;
      device_stream << v.toDevice();
      out << "torch.device(";
      c10::printQuotedString(out, device_stream.str());
      return out << ")";
    }
    case IValue::Tag::GenericDict:
      return printMaybeAnnotatedDict(out, v, formatter);
    case IValue::Tag::Enum: {
      auto enum_holder = v.toEnumHolder();
      return out << enum_holder->qualifiedClassName() << "." <<
          enum_holder->name();
    }
    default:
      TORCH_INTERNAL_ASSERT(false, "repr() not defined on: ", v.tagKind());
  }
}

std::ostream& operator<<(std::ostream& out, const ivalue::EnumHolder& v) {
  out << v.qualifiedClassName() << "." << v.name();
  return out;
}

std::ostream& operator<<(std::ostream & out, const IValue & v) {
  auto formatter = [&](std::ostream& out, const IValue& v) {
    out << v;
  };
  switch(v.tag) {
    case IValue::Tag::None:
      return out << v.toNone();
    case IValue::Tag::Tensor:
      return out << v.toTensor();
    case IValue::Tag::Double: {
      double d = v.toDouble();
      int c = std::fpclassify(d);
      if (c == FP_NORMAL || c == FP_ZERO) {
        int64_t i = int64_t(d);
        if (double(i) == d) {
          return out << i << ".";
        }
      }
      auto orig_prec = out.precision();
      return out
        << std::setprecision(std::numeric_limits<double>::max_digits10)
        << v.toDouble()
        << std::setprecision(orig_prec);
    } case IValue::Tag::Int:
      return out << v.toInt();
    case IValue::Tag::Bool:
      return out << (v.toBool() ? "True" : "False");
    case IValue::Tag::Tuple: {
      const auto& elements = v.toTuple()->elements();
      const auto& finish = elements.size() == 1 ? ",)" : ")";
      return printList(out, elements, "(", finish, formatter);
    }
    case IValue::Tag::String:
      return out << v.toStringRef();
    case IValue::Tag::Blob:
      return out << *v.toBlob();
    case IValue::Tag::Capsule:
      return out << "Capsule";
    case IValue::Tag::GenericList:
      return printList(out, v.toList(), "[", "]", formatter);
    case IValue::Tag::RRef:
      return out << "RRef";
    case IValue::Tag::Future:
      return out << "Future";
    case IValue::Tag::Uninitialized:
      return out << "Uninitialized";
    case IValue::Tag::Device:
      return out << v.toDevice();
    case IValue::Tag::GenericDict:
      return printDict(out, v.toGenericDict(), formatter);
    case IValue::Tag::PyObject: {
      auto py_obj = v.toPyObject();
      return out << "<PyObject at" << py_obj << ">";
    }
    case IValue::Tag::Generator:
      return out << "Generator";
    case IValue::Tag::Quantizer:
      return out << "Quantizer";
    case IValue::Tag::Object: {
      // TODO we should attempt to call __str__ if the object defines it.
      auto obj = v.toObject();
      // print this out the way python would do it
      return out << "<" << obj->name() << " object at " << obj.get() << ">";
    }
    case IValue::Tag::Enum: {
      auto enum_holder = v.toEnumHolder();
      return out << "Enum<" << enum_holder->unqualifiedClassName() << "." <<
          enum_holder->name() << ">";
    }

  }
  AT_ERROR("Tag not found: ", v.tagKind());
}

#undef TORCH_FORALL_TAGS

void IValue::dump() const {
  std::cout << *this << "\n";
}

std::shared_ptr<ClassType> ivalue::Object::type() const {
  return type_.type_->expect<ClassType>();
}

IValue IValue::deepcopy() const {
  IValue::HashAliasedIValueMap memo;
  return deepcopy(memo);
}

IValue IValue::deepcopy(
    IValue::HashAliasedIValueMap& memo) const {
  if (memo.count(*this)) {
    return memo.at(*this);
  }
  IValue copy;
  switch(tag) {
    case IValue::Tag::Tensor:
      copy = IValue(toTensor().clone());
      break;
    case IValue::Tag::Tuple: {
      std::vector<IValue> copied_tuple;
      for (const auto& e : toTuple()->elements()) {
        copied_tuple.push_back(e.deepcopy(memo));
      }
      copy = IValue(ivalue::Tuple::create(copied_tuple));
    }
      break;
    case IValue::Tag::GenericList: {
      auto list = toList();
      auto copied_list = c10::impl::GenericList(list.elementType());
      for (IValue v : list) {
        copied_list.push_back(v.deepcopy(memo));
      }
      copy = IValue(copied_list);
    }
      break;
    case IValue::Tag::GenericDict: {
      auto dict = toGenericDict();
      auto copied_dict = c10::impl::GenericDict(dict.keyType(), dict.valueType());
      for (const auto& entry : dict) {
        copied_dict.insert(entry.key().deepcopy(memo), entry.value().deepcopy(memo));
      }
      copy = IValue(copied_dict);
    }
      break;
    case IValue::Tag::Object: {
      auto class_type = type()->expect<ClassType>();
      if (class_type->hasMethod("__getstate__") &&
          class_type->hasMethod("__setstate__")) {
        copy = ivalue::Object::create(
            c10::StrongTypePtr(class_type->compilation_unit(), type()),
            class_type->numAttributes());
        auto state = class_type->getMethod("__getstate__")({*this});
        class_type->getMethod("__setstate__")({copy, std::move(state)});
      } else {
        copy = IValue(toObject()->deepcopy(memo));
      }
    } break;
    case IValue::Tag::String:
    case IValue::Tag::None:
    case IValue::Tag::Double:
    case IValue::Tag::Int:
    case IValue::Tag::Bool:
    case IValue::Tag::Device:
    case IValue::Tag::Uninitialized: {
      copy = *this;
    } break;
    default: {
      AT_ERROR("Can't deepcopy IValue with tag: ", tagKind());
    }
  }
  // NB: this doesn't work if an object contains itself, and it may
  // come up in the future when we expand the object system, we will
  // have a follow up PR to fix this when it becomes an issue.
  if (!isAliasOf(copy)) {
    memo[*this] = copy;
  }
  return copy;
}

std::string ivalue::Object::name() const {
  return type()->name()->qualifiedName();
}

IValue ivalue::Object::getAttr(const std::string& name) const {
  const size_t slot = type()->getAttributeSlot(name);
  return getSlot(slot);
}

void ivalue::Object::setAttr(const std::string& name, IValue v) {
  const size_t slot = type()->getAttributeSlot(name);
  setSlot(slot, std::move(v));
}

void ivalue::Object::unsafeRemoveAttr(const std::string& name) {
  const size_t slot = type()->getAttributeSlot(name);
  unsafeRemoveSlot(slot);
}

void ivalue::Object::resizeObject(size_t slot) {
  AT_ASSERT(slot < type()->numAttributes());
  slots_.resize(type()->numAttributes());
}

c10::intrusive_ptr<ivalue::Object> ivalue::Object::copy() const {
  auto object = ivalue::Object::create(c10::StrongTypePtr(type_.cu_, type()), type()->numAttributes());
  for (auto i = 0; i < slots_.size(); ++i) {
    object->setSlot(i, slots_[i]);
  }
  return object;
}

c10::intrusive_ptr<ivalue::Object> ivalue::Object::deepcopy() const {
  IValue::HashAliasedIValueMap memo;
  return deepcopy(memo);
}

c10::intrusive_ptr<ivalue::Object> ivalue::Object::deepcopy(IValue::HashAliasedIValueMap& memo) const {
  auto object = ivalue::Object::create(c10::StrongTypePtr(type_.cu_, type()), type()->numAttributes());
  for (size_t i = 0; i < slots_.size(); ++i) {
    if (slots_[i].type() == c10::CapsuleType::get()) {
      // If we've gotten here, it means that we have *not* copied this
      // class via __getstate__ and __setstate__. That fact and the
      // fact that we have a Capsule attribute mean that this is a
      // custom C++ class without serialization methods defined.
      std::stringstream err;
      err << "Cannot serialize custom bound C++ class";
      if (auto qualname = type()->name()) {
        err << " " << qualname->qualifiedName();
      }
      err << ". Please define serialization methods via def_pickle() for "
            "this class.";
      AT_ERROR(err.str());
    }
    object->setSlot(i, slots_[i].deepcopy(memo));
  }
  return object;
}

StrongTypePtr::StrongTypePtr(
    std::shared_ptr<torch::jit::CompilationUnit> cu,
    std::shared_ptr<Type> type) {
  cu_ = std::move(cu);
  type_ = type;
  TORCH_INTERNAL_ASSERT(type_);
}

ska::flat_hash_map<std::type_index, c10::ClassTypePtr>& getCustomClassTypeMap() {
    static ska::flat_hash_map<std::type_index, c10::ClassTypePtr> tmap;
    return tmap;
}

std::unordered_map<std::string, std::function<PyObject*(void*)>>&
getClassConverter() {
  static std::unordered_map<std::string, std::function<PyObject*(void*)>>
      classConverter;
  return classConverter;
}

CAFFE2_API intrusive_ptr<ivalue::Future> collectAll(
    List<intrusive_ptr<ivalue::Future>> srcs) {
  struct Ctx {
    explicit Ctx(List<intrusive_ptr<ivalue::Future>> srcs)
        : remaining(srcs.size()),
          srcFutures(std::move(srcs)),
          asIvalue(srcFutures),
          dstFuture(make_intrusive<ivalue::Future>(asIvalue.type())) {}
    std::atomic<int32_t> remaining{0};
    List<intrusive_ptr<ivalue::Future>> srcFutures;
    IValue asIvalue;
    intrusive_ptr<ivalue::Future> dstFuture;
  };

  auto ctx = std::make_shared<Ctx>(std::move(srcs));
  std::function<void()> func = [ctx]() {
    if (--ctx->remaining == 0) {
      ctx->dstFuture->markCompleted(ctx->asIvalue);
    }
  };
  if (ctx->srcFutures.size() == 0) {
    ctx->dstFuture->markCompleted(ctx->asIvalue);
  } else {
    auto typePtr = ctx->srcFutures.get(0)->elementType();
    for (int32_t tot = ctx->srcFutures.size(), i = 0; i < tot; ++i) {
      TORCH_CHECK(i == 0 || *ctx->srcFutures.get(i)->elementType() == *typePtr);
      ctx->srcFutures.get(i)->addCallback(func);
    }
  }
  return ctx->dstFuture;
}

CAFFE2_API intrusive_ptr<ivalue::Future> collectAny(
    List<intrusive_ptr<ivalue::Future>> srcs) {
  if (srcs.empty()) {
    auto res = make_intrusive<ivalue::Future>(NoneType::get());
    res->markCompleted();
    return res;
  }
  TypePtr typePtr = srcs.get(0)->elementType();
  for (size_t i = 0, tot = srcs.size(); i < tot; ++i) {
    if (srcs.get(i)->completed()) {
      return srcs.get(i);
    }
    TORCH_CHECK(i == 0 || (*typePtr == *srcs.get(i)->elementType()));
  }
  struct Ctx {
    explicit Ctx(List<intrusive_ptr<ivalue::Future>> srcs, TypePtr typePtr)
        : srcFutures(std::move(srcs)),
          dstFuture(make_intrusive<ivalue::Future>(typePtr)) {}
    std::atomic<bool> done{false};
    List<intrusive_ptr<ivalue::Future>> srcFutures;
    intrusive_ptr<ivalue::Future> dstFuture;
  };
  auto ctx = std::make_shared<Ctx>(std::move(srcs), typePtr);
  std::function<void(size_t)> func = [ctx](size_t index) {
    if (!ctx->done.exchange(true)) {
      intrusive_ptr<ivalue::Future> dst = ctx->dstFuture;
      intrusive_ptr<ivalue::Future> src = ctx->srcFutures.get(index);
      ctx->dstFuture.reset(); // Once future is satisfied, remove refs.
      ctx->srcFutures =
          List<intrusive_ptr<ivalue::Future>>(ctx->srcFutures.elementType());
      if (src->hasError()) {
        dst->setError(*src->error());
      } else {
        dst->markCompleted(src->constValue());
      }
    }
  };
  for (size_t tot = ctx->srcFutures.size(), i = 0; i < tot; ++i) {
    ctx->srcFutures.get(i)->addCallback([func, i]() { func(i); });
  }
  return ctx->dstFuture;
}

} // namespace c10