src/dawn/tests/unittests/WeakRefTests.cpp

// Copyright 2023 The Dawn & Tint Authors
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#include <functional>
#include <thread>

#include "absl/container/flat_hash_map.h"
#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 = GetWeakRef(base);
    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 = GetWeakRef(base);
    WeakRef<WeakRefBaseA> weak2 = weak1;
    WeakRef<WeakRefBaseA> weak3 = GetWeakRef(base);
    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 = GetWeakRef(base);
        semA.Release();
        semB.Acquire();
        EXPECT_EQ(weak.Promote().Get(), nullptr);
        semA.Release();
    };
    std::thread t(f);

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

// Try using WeakRef as keys in a hash map.
TEST(WeakRefTests, WeakRefHashmapKey) {
    Ref<WeakRefBaseA> base1 = AcquireRef(new WeakRefBaseA());
    WeakRef<WeakRefBaseA> weak1 = GetWeakRef(base1);
    Ref<WeakRefBaseA> base2 = AcquireRef(new WeakRefBaseA());
    WeakRef<WeakRefBaseA> weak2 = GetWeakRef(base2);

    absl::flat_hash_map<WeakRef<WeakRefBaseA>, int> m;
    m.insert({weak1, 1});
    m.insert({weak2, 2});

    // Getting the values should match w.r.t the map.
    EXPECT_EQ(m[weak1], 1);
    EXPECT_EQ(m[weak2], 2);

    // Getting the values with copies of the keys should work.
    auto copy1 = weak1;
    auto copy2 = weak2;
    EXPECT_EQ(m[copy1], 1);
    EXPECT_EQ(m[copy2], 2);

    // Getting the values with a new weak ref should work.
    EXPECT_EQ(m[GetWeakRef(base1)], 1);
    EXPECT_EQ(m[GetWeakRef(base2)], 2);

    // Getting values should still work after the actual reference is gone.
    base1 = nullptr;
    base2 = nullptr;
    EXPECT_EQ(m[weak1], 1);
    EXPECT_EQ(m[weak2], 2);
    EXPECT_EQ(m[copy1], 1);
    EXPECT_EQ(m[copy2], 2);

    // Finding from the map should be valid, but promotion should fail.
    auto it = m.find(weak1);
    ASSERT_TRUE(it != m.end());
    EXPECT_EQ(it->second, 1);
    EXPECT_EQ(it->first.Promote(), nullptr);
}

}  // 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(GetWeakRef(std::declval<T*>()));
TEST(WeakRefTests, GetWeakRefFromPtr) {
    // 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.");
}

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

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

}  // anonymous namespace
}  // namespace dawn

#endif