src/dawn/tests/unittests/WeakRefTests.cpp

// Copyright 2023 The Dawn 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.

#include <functional>
#include <thread>

#include "dawn/common/WeakRef.h"
#include "dawn/common/WeakRefSupport.h"
#include "dawn/utils/BinarySemaphore.h"
#include "gtest/gtest.h"

namespace dawn {
namespace {

using utils::BinarySemaphore;

class RefCountedT : public RefCounted {};

class WeakRefBaseA : public RefCounted, public WeakRefSupport<WeakRefBaseA> {
  public:
    WeakRefBaseA() = default;
    explicit WeakRefBaseA(std::function<void(WeakRefBaseA*)> deleteFn) : mDeleteFn(deleteFn) {}

  protected:
    ~WeakRefBaseA() override { mDeleteFn(this); }

  private:
    std::function<void(WeakRefBaseA*)> mDeleteFn = [](WeakRefBaseA*) -> void {};
};

class WeakRefDerivedA : public WeakRefBaseA {
  public:
    WeakRefDerivedA() = default;
    explicit WeakRefDerivedA(std::function<void(WeakRefBaseA*)> deleteFn)
        : WeakRefBaseA(deleteFn) {}
};

class WeakRefBaseB : public RefCounted, public WeakRefSupport<WeakRefBaseB> {};
class WeakRefDerivedB : public WeakRefBaseB {};

// When the original refcounted object is destroyed, all WeakRefs are no longer able to Promote.
TEST(WeakRefTests, BasicPromote) {
    Ref<WeakRefBaseA> base = AcquireRef(new WeakRefBaseA());
    WeakRef<WeakRefBaseA> weak = base.GetWeakRef();
    EXPECT_EQ(weak.Promote().Get(), base.Get());

    base = nullptr;
    EXPECT_EQ(weak.Promote().Get(), nullptr);
}

// When the original refcounted object is destroyed, all WeakRefs, including upcasted ones, are no
// longer able to Promote.
TEST(WeakRefTests, DerivedPromote) {
    Ref<WeakRefDerivedA> base = AcquireRef(new WeakRefDerivedA());
    WeakRef<WeakRefDerivedA> weak1 = base.GetWeakRef();
    WeakRef<WeakRefBaseA> weak2 = weak1;
    WeakRef<WeakRefBaseA> weak3 = base.GetWeakRef();
    EXPECT_EQ(weak1.Promote().Get(), base.Get());
    EXPECT_EQ(weak2.Promote().Get(), base.Get());
    EXPECT_EQ(weak3.Promote().Get(), base.Get());

    base = nullptr;
    EXPECT_EQ(weak1.Promote().Get(), nullptr);
    EXPECT_EQ(weak2.Promote().Get(), nullptr);
    EXPECT_EQ(weak3.Promote().Get(), nullptr);
}

// Trying to promote a WeakRef to a Ref while the original value is being destroyed returns nullptr.
TEST(WeakRefTests, DeletingAndPromoting) {
    BinarySemaphore semA, semB;
    Ref<WeakRefBaseA> base = AcquireRef(new WeakRefBaseA([&](WeakRefBaseA*) {
        semB.Release();
        semA.Acquire();
    }));

    auto f = [&] {
        WeakRef<WeakRefBaseA> weak = base.GetWeakRef();
        semA.Release();
        semB.Acquire();
        EXPECT_EQ(weak.Promote().Get(), nullptr);
        semA.Release();
    };
    std::thread t(f);

    semA.Acquire();
    base = nullptr;
    t.join();
}

}  // anonymous namespace
}  // namespace dawn

// Special compilation tests that are only enabled when experimental headers are available.
#if __has_include(<experimental/type_traits>)
#include <experimental/type_traits>

namespace dawn {
namespace {

// Helper detection utilities for verifying that unintended assignments are not allowed.
template <typename L, typename R>
using weakref_copyable_t =
    decltype(std::declval<WeakRef<L>&>() = std::declval<const WeakRef<R>&>());
template <typename L, typename R>
using weakref_movable_t =
    decltype(std::declval<WeakRef<L>&>() = std::declval<const WeakRef<R>&&>());
TEST(WeakRefTests, CrossTypesAssignments) {
    // Same type and upcasting is allowed.
    static_assert(std::experimental::is_detected_v<weakref_copyable_t, WeakRefBaseA, WeakRefBaseA>,
                  "Same type copy assignment is allowed.");
    static_assert(std::experimental::is_detected_v<weakref_movable_t, WeakRefBaseA, WeakRefBaseA>,
                  "Same type move assignment is allowed.");

    static_assert(
        std::experimental::is_detected_v<weakref_copyable_t, WeakRefBaseA, WeakRefDerivedA>,
        "Upcasting type copy assignment is allowed.");
    static_assert(
        std::experimental::is_detected_v<weakref_movable_t, WeakRefBaseA, WeakRefDerivedA>,
        "Upcasting type move assignment is allowed.");

    // Same type, but down casting is not allowed.
    static_assert(
        !std::experimental::is_detected_v<weakref_copyable_t, WeakRefDerivedA, WeakRefBaseA>,
        "Downcasting type copy assignment is not allowed.");
    static_assert(
        !std::experimental::is_detected_v<weakref_movable_t, WeakRefDerivedA, WeakRefBaseA>,
        "Downcasting type move assignment is not allowed.");

    // Cross types are not allowed.
    static_assert(!std::experimental::is_detected_v<weakref_copyable_t, WeakRefBaseA, WeakRefBaseB>,
                  "Cross type copy assignment is not allowed.");
    static_assert(!std::experimental::is_detected_v<weakref_movable_t, WeakRefBaseA, WeakRefBaseB>,
                  "Cross type move assignment is not allowed.");
    static_assert(
        !std::experimental::is_detected_v<weakref_copyable_t, WeakRefBaseA, WeakRefDerivedB>,
        "Cross type upcasting copy assignment is not allowed.");
    static_assert(
        !std::experimental::is_detected_v<weakref_movable_t, WeakRefBaseA, WeakRefDerivedB>,
        "Cross type upcasting move assignment is not allowed.");
}

// Helper detection utilty to verify whether GetWeakRef is enabled.
template <typename T>
using can_get_weakref_t = decltype(std::declval<Ref<T>>().GetWeakRef());
TEST(WeakRefTests, GetWeakRef) {
    // The GetWeakRef function is only available on types that extend WeakRefSupport.
    static_assert(std::experimental::is_detected_v<can_get_weakref_t, WeakRefBaseA>,
                  "GetWeakRef is enabled on classes that directly extend WeakRefSupport.");
    static_assert(std::experimental::is_detected_v<can_get_weakref_t, WeakRefDerivedA>,
                  "GetWeakRef is enabled on classes that indirectly extend WeakRefSupport.");

    static_assert(!std::experimental::is_detected_v<can_get_weakref_t, RefCountedT>,
                  "GetWeakRef is disabled on classes that do not extend WeakRefSupport.");
}

}  // anonymous namespace
}  // namespace dawn

#endif