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Add aliasing constructor to Shared #602

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1 commit merged into from
Feb 14, 2024
Merged

Add aliasing constructor to Shared #602

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25 changes: 25 additions & 0 deletions common/memory.h
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Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,27 @@ class ABSL_ATTRIBUTE_TRIVIAL_ABI Shared final {
// NOLINTNEXTLINE(google-explicit-constructor)
explicit Shared(SharedView<U> other);

// An aliasing constructor. The resulting `Shared` shares ownership
// information with `alias`, but holds an unmanaged pointer to `T`.
//
// Usage:
// Shared<Object> object;
// Shared<Member> member = Shared<Member>(object, &object->member);
template <typename U>
Shared(const Shared<U>& alias, T* ptr)
: value_(ptr), refcount_(alias.refcount_) {
common_internal::StrongRef(refcount_);
}

// An aliasing constructor. The resulting `Shared` shares ownership
// information with `alias`, but holds an unmanaged pointer to `T`.
template <typename U>
Shared(Shared<U>&& alias, T* ptr) noexcept
: value_(ptr), refcount_(alias.refcount_) {
alias.value_ = nullptr;
alias.refcount_ = nullptr;
}

~Shared() { common_internal::StrongUnref(refcount_); }

Shared& operator=(const Shared& other) {
Expand Down Expand Up @@ -245,6 +266,10 @@ class ABSL_ATTRIBUTE_TRIVIAL_ABI SharedView final {
SharedView(const Shared<U>& other ABSL_ATTRIBUTE_LIFETIME_BOUND) noexcept
: value_(other.value_), refcount_(other.refcount_) {}

template <typename U>
SharedView(SharedView<U> alias, T* ptr)
: value_(ptr), refcount_(alias.refcount_) {}

template <
typename U,
typename = std::enable_if_t<std::conjunction_v<
Expand Down
52 changes: 52 additions & 0 deletions common/memory_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -233,6 +233,8 @@ class Object {
}
}

int member = 0;

private:
bool* deleted_;
};
Expand Down Expand Up @@ -260,6 +262,56 @@ TEST_P(MemoryManagerTest, Shared) {
Finish();
}

TEST_P(MemoryManagerTest, SharedAliasCopy) {
bool deleted = false;
{
auto object = memory_manager().MakeShared<Object>(deleted);
EXPECT_TRUE(object);
EXPECT_FALSE(deleted);
{
auto member = Shared<int>(object, &object->member);
EXPECT_TRUE(object);
EXPECT_FALSE(deleted);
EXPECT_TRUE(member);
}
EXPECT_TRUE(object);
EXPECT_FALSE(deleted);
}
switch (memory_management()) {
case MemoryManagement::kPooling:
EXPECT_FALSE(deleted);
break;
case MemoryManagement::kReferenceCounting:
EXPECT_TRUE(deleted);
break;
}
Finish();
}

TEST_P(MemoryManagerTest, SharedAliasMove) {
bool deleted = false;
{
auto object = memory_manager().MakeShared<Object>(deleted);
EXPECT_TRUE(object);
EXPECT_FALSE(deleted);
{
auto member = Shared<int>(std::move(object), &object->member);
EXPECT_FALSE(object);
EXPECT_FALSE(deleted);
EXPECT_TRUE(member);
}
switch (memory_management()) {
case MemoryManagement::kPooling:
EXPECT_FALSE(deleted);
break;
case MemoryManagement::kReferenceCounting:
EXPECT_TRUE(deleted);
break;
}
}
Finish();
}

TEST_P(MemoryManagerTest, SharedCopyConstruct) {
bool deleted = false;
{
Expand Down