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Basics of make_shared with anonymous union

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Steven Dee (Jōshin) 2024-06-19 22:53:37 -07:00
parent 0b710a112d
commit da5817816d
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2 changed files with 63 additions and 0 deletions
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52
ctl/shared_ptr.h
View file

@ -2,6 +2,7 @@
// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
#ifndef COSMOPOLITAN_CTL_SHARED_PTR_H_
#define COSMOPOLITAN_CTL_SHARED_PTR_H_
#include "new.h"
#include "unique_ptr.h"
namespace ctl {
@ -72,6 +73,39 @@ struct shared_pointer : shared_control
}
};
template <typename T>
struct shared_emplace : shared_control
{
union {
T t;
};
template <typename... Args>
void construct(Args&&... args) {
::new (&t) T(ctl::forward<Args>(args)...);
}
static unique_ptr<shared_emplace> make_unique()
{
return new shared_emplace();
}
private:
explicit constexpr shared_emplace() noexcept
{
}
void on_zero_shared() noexcept override
{
t.~T();
}
void on_zero_weak() noexcept override
{
delete this;
}
};
} // namespace __
struct bad_weak_ptr : ctl::exception
@ -203,10 +237,28 @@ class shared_ptr
// TODO(mrdomino): owner_before(weak_ptr const&)
private:
constexpr shared_ptr(T* const p, __::shared_control* rc) noexcept
: p(p), rc(rc)
{
}
template <typename U, typename... Args>
friend shared_ptr<U> make_shared(Args&&... args);
T* p;
__::shared_control* rc;
};
template <typename T, typename... Args>
shared_ptr<T> make_shared(Args&&... args)
{
auto rc = __::shared_emplace<T>::make_unique();
rc->construct(ctl::forward<Args>(args)...);
auto r = shared_ptr<T>(&rc->t, rc.get());
rc.release();
return r;
}
// TODO(mrdomino): non-member functions (make_shared et al)
// TODO(mrdomino): weak_ptr

11
test/ctl/shared_ptr_test.cc
View file

@ -24,6 +24,11 @@
template<typename T>
using Ptr = ctl::shared_ptr<T>;
template <typename T, typename... Args>
Ptr<T> Mk(Args&&... args) {
return ctl::make_shared<T>(ctl::forward<Args>(args)...);
}
#undef ctl
int
@ -62,6 +67,12 @@ main()
}
#endif
{
auto x = Mk<int>(5);
if (x.use_count() != 1)
return 8;
}
// TODO(mrdomino): exercise more of API
// TODO(mrdomino): threading stress-test