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// Copyright 2021 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef GRPC_SRC_CORE_LIB_PROMISE_IF_H
#define GRPC_SRC_CORE_LIB_PROMISE_IF_H
#include <grpc/support/port_platform.h>
#include <memory>
#include <type_traits>
#include <utility>
#include "y_absl/status/statusor.h"
#include "y_absl/types/variant.h"
#include "src/core/lib/gprpp/construct_destruct.h"
#include "src/core/lib/promise/detail/promise_factory.h"
#include "src/core/lib/promise/detail/promise_like.h"
#include "src/core/lib/promise/poll.h"
namespace grpc_core {
namespace promise_detail {
template <typename CallPoll, typename T, typename F>
typename CallPoll::PollResult ChooseIf(CallPoll call_poll, bool result,
T* if_true, F* if_false) {
if (result) {
auto promise = if_true->Make();
return call_poll(promise);
} else {
auto promise = if_false->Make();
return call_poll(promise);
}
}
template <typename CallPoll, typename T, typename F>
typename CallPoll::PollResult ChooseIf(CallPoll call_poll,
y_absl::StatusOr<bool> result, T* if_true,
F* if_false) {
if (!result.ok()) {
return typename CallPoll::PollResult(result.status());
} else if (*result) {
auto promise = if_true->Make();
return call_poll(promise);
} else {
auto promise = if_false->Make();
return call_poll(promise);
}
}
template <typename C, typename T, typename F>
class If {
private:
using TrueFactory = promise_detail::OncePromiseFactory<void, T>;
using FalseFactory = promise_detail::OncePromiseFactory<void, F>;
using ConditionPromise = PromiseLike<C>;
using TruePromise = typename TrueFactory::Promise;
using FalsePromise = typename FalseFactory::Promise;
using Result =
typename PollTraits<decltype(std::declval<TruePromise>()())>::Type;
public:
If(C condition, T if_true, F if_false)
: state_(Evaluating{ConditionPromise(std::move(condition)),
TrueFactory(std::move(if_true)),
FalseFactory(std::move(if_false))}) {}
Poll<Result> operator()() {
return y_absl::visit(CallPoll<false>{this}, state_);
}
private:
struct Evaluating {
ConditionPromise condition;
TrueFactory if_true;
FalseFactory if_false;
};
using State = y_absl::variant<Evaluating, TruePromise, FalsePromise>;
State state_;
template <bool kSetState>
struct CallPoll {
using PollResult = Poll<Result>;
If* const self;
PollResult operator()(Evaluating& evaluating) const {
static_assert(
!kSetState,
"shouldn't need to set state coming through the initial branch");
auto r = evaluating.condition();
if (auto* p = r.value_if_ready()) {
return ChooseIf(CallPoll<true>{self}, std::move(*p),
&evaluating.if_true, &evaluating.if_false);
}
return Pending();
}
template <class Promise>
PollResult operator()(Promise& promise) const {
auto r = promise();
if (kSetState && r.pending()) {
self->state_.template emplace<Promise>(std::move(promise));
}
return r;
}
};
};
template <typename T, typename F>
class If<bool, T, F> {
private:
using TrueFactory = promise_detail::OncePromiseFactory<void, T>;
using FalseFactory = promise_detail::OncePromiseFactory<void, F>;
using TruePromise = typename TrueFactory::Promise;
using FalsePromise = typename FalseFactory::Promise;
using Result =
typename PollTraits<decltype(std::declval<TruePromise>()())>::Type;
public:
If(bool condition, T if_true, F if_false) : condition_(condition) {
TrueFactory true_factory(std::move(if_true));
FalseFactory false_factory(std::move(if_false));
if (condition_) {
Construct(&if_true_, true_factory.Make());
} else {
Construct(&if_false_, false_factory.Make());
}
}
~If() {
if (condition_) {
Destruct(&if_true_);
} else {
Destruct(&if_false_);
}
}
If(const If&) = delete;
If& operator=(const If&) = delete;
If(If&& other) noexcept : condition_(other.condition_) {
if (condition_) {
Construct(&if_true_, std::move(other.if_true_));
} else {
Construct(&if_false_, std::move(other.if_false_));
}
}
If& operator=(If&& other) noexcept {
if (&other == this) return *this;
Destruct(this);
Construct(this, std::move(other));
return *this;
}
Poll<Result> operator()() {
#ifndef NDEBUG
asan_canary_ = std::make_unique<int>(1 + *asan_canary_);
#endif
if (condition_) {
return if_true_();
} else {
return if_false_();
}
}
private:
bool condition_;
union {
TruePromise if_true_;
FalsePromise if_false_;
};
// Make failure to destruct show up in ASAN builds.
#ifndef NDEBUG
std::unique_ptr<int> asan_canary_ = std::make_unique<int>(0);
#endif
};
} // namespace promise_detail
// If promise combinator.
// Takes 3 promise factories, and evaluates the first.
// If it returns failure, returns failure for the entire combinator.
// If it returns true, evaluates the second promise.
// If it returns false, evaluates the third promise.
template <typename C, typename T, typename F>
promise_detail::If<C, T, F> If(C condition, T if_true, F if_false) {
return promise_detail::If<C, T, F>(std::move(condition), std::move(if_true),
std::move(if_false));
}
} // namespace grpc_core
#endif // GRPC_SRC_CORE_LIB_PROMISE_IF_H
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