Basic CTL shared_ptr implementation (#1267)

ctl/shared_ptr.h

@@ -0,0 +1,454 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_SHARED_PTR_H_
+#define CTL_SHARED_PTR_H_
+
+#include "exception.h"
+#include "is_convertible.h"
+#include "remove_extent.h"
+#include "unique_ptr.h"
+
+// XXX currently needed to use placement-new syntax (move to cxx.inc?)
+void*
+operator new(size_t, void*) noexcept;
+
+namespace ctl {
+
+class bad_weak_ptr : public exception
+{
+  public:
+    const char* what() const noexcept override
+    {
+        return "ctl::bad_weak_ptr";
+    }
+};
+
+namespace __ {
+
+template<typename T>
+struct ptr_ref
+{
+    using type = T&;
+};
+
+template<>
+struct ptr_ref<void>
+{
+    using type = void;
+};
+
+static inline __attribute__((always_inline)) void
+incref(size_t* r) noexcept
+{
+#ifdef NDEBUG
+    __atomic_fetch_add(r, 1, __ATOMIC_RELAXED);
+#else
+    size_t refs = __atomic_fetch_add(r, 1, __ATOMIC_RELAXED);
+    if (refs > ((size_t)-1) >> 1)
+        __builtin_trap();
+#endif
+}
+
+static inline __attribute__((always_inline)) bool
+decref(size_t* r) noexcept
+{
+    if (!__atomic_fetch_sub(r, 1, __ATOMIC_RELEASE)) {
+        __atomic_thread_fence(__ATOMIC_ACQUIRE);
+        return true;
+    }
+    return false;
+}
+
+class shared_ref
+{
+  public:
+    constexpr shared_ref() noexcept = default;
+    shared_ref(const shared_ref&) = delete;
+    shared_ref& operator=(const shared_ref&) = delete;
+
+    virtual ~shared_ref() = default;
+
+    void keep_shared() noexcept
+    {
+        incref(&shared);
+    }
+
+    void drop_shared() noexcept
+    {
+        if (decref(&shared)) {
+            dispose();
+            drop_weak();
+        }
+    }
+
+    void keep_weak() noexcept
+    {
+        incref(&weak);
+    }
+
+    void drop_weak() noexcept
+    {
+        if (decref(&weak)) {
+            delete this;
+        }
+    }
+
+    size_t use_count() const noexcept
+    {
+        return shared + 1;
+    }
+
+    size_t weak_count() const noexcept
+    {
+        return weak;
+    }
+
+  private:
+    virtual void dispose() noexcept = 0;
+
+    size_t shared = 0;
+    size_t weak = 0;
+};
+
+template<typename T, typename D>
+class shared_pointer : public shared_ref
+{
+  public:
+    static shared_pointer* make(T* const p, D d)
+    {
+        return make(unique_ptr<T, D>(p, move(d)));
+    }
+
+    static shared_pointer* make(unique_ptr<T, D> p)
+    {
+        return new shared_pointer(p.release(), move(p.get_deleter()));
+    }
+
+  private:
+    shared_pointer(T* const p, D d) noexcept : p(p), d(move(d))
+    {
+    }
+
+    void dispose() noexcept override
+    {
+        move(d)(p);
+    }
+
+    T* const p;
+    [[no_unique_address]] D d;
+};
+
+template<typename T>
+class shared_emplace : public shared_ref
+{
+  public:
+    union
+    {
+        T t;
+    };
+
+    template<typename... Args>
+    void construct(Args&&... args)
+    {
+        ::new (&t) T(forward<Args>(args)...);
+    }
+
+    static unique_ptr<shared_emplace> make()
+    {
+        return unique_ptr(new shared_emplace());
+    }
+
+  private:
+    explicit constexpr shared_emplace() noexcept = default;
+
+    void dispose() noexcept override
+    {
+        t.~T();
+    }
+};
+
+template<typename T, typename U>
+concept shared_ptr_compatible = is_convertible_v<U*, T*>;
+
+} // namespace __
+
+template<typename T>
+class weak_ptr;
+
+template<typename T>
+class shared_ptr
+{
+  public:
+    using element_type = remove_extent_t<T>;
+    using weak_type = weak_ptr<T>;
+
+    constexpr shared_ptr() noexcept = default;
+    constexpr shared_ptr(nullptr_t) noexcept
+    {
+    }
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    explicit shared_ptr(U* const p) : shared_ptr(p, default_delete<U>())
+    {
+    }
+
+    template<typename U, typename D>
+        requires __::shared_ptr_compatible<T, U>
+    shared_ptr(U* const p, D d)
+      : p(p), rc(__::shared_pointer<U, D>::make(p, move(d)))
+    {
+    }
+
+    template<typename U>
+    shared_ptr(const shared_ptr<U>& r, element_type* p) noexcept
+      : p(p), rc(r.rc)
+    {
+        if (rc)
+            rc->keep_shared();
+    }
+
+    template<typename U>
+    shared_ptr(shared_ptr<U>&& r, element_type* p) noexcept : p(p), rc(r.rc)
+    {
+        r.p = nullptr;
+        r.rc = nullptr;
+    }
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    shared_ptr(const shared_ptr<U>& r) noexcept : p(r.p), rc(r.rc)
+    {
+        if (rc)
+            rc->keep_shared();
+    }
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    shared_ptr(shared_ptr<U>&& r) noexcept : p(r.p), rc(r.rc)
+    {
+        r.p = nullptr;
+        r.rc = nullptr;
+    }
+
+    shared_ptr(const shared_ptr& r) noexcept : p(r.p), rc(r.rc)
+    {
+        if (rc)
+            rc->keep_shared();
+    }
+
+    shared_ptr(shared_ptr&& r) noexcept : p(r.p), rc(r.rc)
+    {
+        r.p = nullptr;
+        r.rc = nullptr;
+    }
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    explicit shared_ptr(const weak_ptr<U>& r) : p(r.p), rc(r.rc)
+    {
+        if (r.expired()) {
+            throw bad_weak_ptr();
+        }
+        rc->keep_shared();
+    }
+
+    template<typename U, typename D>
+        requires __::shared_ptr_compatible<T, U>
+    shared_ptr(unique_ptr<U, D>&& r)
+      : p(r.p), rc(__::shared_pointer<U, D>::make(move(r)))
+    {
+    }
+
+    ~shared_ptr()
+    {
+        if (rc)
+            rc->drop_shared();
+    }
+
+    shared_ptr& operator=(shared_ptr r) noexcept
+    {
+        swap(r);
+        return *this;
+    }
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    shared_ptr& operator=(shared_ptr<U> r) noexcept
+    {
+        shared_ptr<T>(move(r)).swap(*this);
+        return *this;
+    }
+
+    void reset() noexcept
+    {
+        shared_ptr().swap(*this);
+    }
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    void reset(U* const p2)
+    {
+        shared_ptr<T>(p2).swap(*this);
+    }
+
+    template<typename U, typename D>
+        requires __::shared_ptr_compatible<T, U>
+    void reset(U* const p2, D d)
+    {
+        shared_ptr<T>(p2, d).swap(*this);
+    }
+
+    void swap(shared_ptr& r) noexcept
+    {
+        using ctl::swap;
+        swap(p, r.p);
+        swap(rc, r.rc);
+    }
+
+    element_type* get() const noexcept
+    {
+        return p;
+    }
+
+    typename __::ptr_ref<T>::type operator*() const noexcept
+    {
+        if (!p)
+            __builtin_trap();
+        return *p;
+    }
+
+    T* operator->() const noexcept
+    {
+        if (!p)
+            __builtin_trap();
+        return p;
+    }
+
+    long use_count() const noexcept
+    {
+        return rc ? rc->use_count() : 0;
+    }
+
+    explicit operator bool() const noexcept
+    {
+        return p;
+    }
+
+    template<typename U>
+    bool owner_before(const shared_ptr<U>& r) const noexcept
+    {
+        return p < r.p;
+    }
+
+    template<typename U>
+    bool owner_before(const weak_ptr<U>& r) const noexcept
+    {
+        return !r.owner_before(*this);
+    }
+
+  private:
+    template<typename U>
+    friend class weak_ptr;
+
+    template<typename U>
+    friend class shared_ptr;
+
+    template<typename U, typename... Args>
+    friend shared_ptr<U> make_shared(Args&&... args);
+
+    element_type* p = nullptr;
+    __::shared_ref* rc = nullptr;
+};
+
+template<typename T>
+class weak_ptr
+{
+  public:
+    using element_type = remove_extent_t<T>;
+
+    constexpr weak_ptr() noexcept = default;
+
+    template<typename U>
+        requires __::shared_ptr_compatible<T, U>
+    weak_ptr(const shared_ptr<U>& r) noexcept : p(r.p), rc(r.rc)
+    {
+        if (rc)
+            rc->keep_weak();
+    }
+
+    ~weak_ptr()
+    {
+        if (rc)
+            rc->drop_weak();
+    }
+
+    long use_count() const noexcept
+    {
+        return rc ? rc->use_count() : 0;
+    }
+
+    bool expired() const noexcept
+    {
+        return !use_count();
+    }
+
+    void reset() noexcept
+    {
+        weak_ptr().swap(*this);
+    }
+
+    void swap(weak_ptr& r) noexcept
+    {
+        using ctl::swap;
+        swap(p, r.p);
+        swap(rc, r.rc);
+    }
+
+    shared_ptr<T> lock() const noexcept
+    {
+        if (expired())
+            return nullptr;
+        shared_ptr<T> r;
+        r.p = p;
+        r.rc = rc;
+        if (rc)
+            rc->keep_shared();
+        return r;
+    }
+
+    template<typename U>
+    bool owner_before(const weak_ptr<U>& r) const noexcept
+    {
+        return p < r.p;
+    }
+
+    template<typename U>
+    bool owner_before(const shared_ptr<U>& r) const noexcept
+    {
+        return p < r.p;
+    }
+
+  private:
+    template<typename U>
+    friend class shared_ptr;
+
+    element_type* p = nullptr;
+    __::shared_ref* rc = nullptr;
+};
+
+template<typename T, typename... Args>
+shared_ptr<T>
+make_shared(Args&&... args)
+{
+    auto rc = __::shared_emplace<T>::make();
+    rc->construct(forward<Args>(args)...);
+    shared_ptr<T> r;
+    r.p = &rc->t;
+    r.rc = rc.release();
+    return r;
+}
+
+} // namespace ctl
+
+#endif // CTL_SHARED_PTR_H_