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This code does not segfault and it compiles cleanly, and it took a while to get here.
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// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*- | ||
// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi | ||
// | ||
// Copyright 2024 Justine Alexandra Roberts Tunney | ||
// | ||
// Permission to use, copy, modify, and/or distribute this software for | ||
// any purpose with or without fee is hereby granted, provided that the | ||
// above copyright notice and this permission notice appear in all copies. | ||
// | ||
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL | ||
// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED | ||
// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE | ||
// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL | ||
// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR | ||
// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER | ||
// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR | ||
// PERFORMANCE OF THIS SOFTWARE. | ||
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#include "shared_ptr.h" | ||
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#include "libc/intrin/atomic.h" | ||
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namespace { | ||
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inline void incref(_Atomic(size_t)* r) | ||
{ | ||
size_t r2 = atomic_fetch_add_explicit(r, 1, memory_order_relaxed); | ||
if (r2 > ((size_t)-1) >> 1) | ||
__builtin_trap(); | ||
} | ||
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inline int decref(_Atomic(size_t)* r) | ||
{ | ||
if (!atomic_fetch_sub_explicit(r, 1, memory_order_release)) { | ||
atomic_thread_fence(memory_order_acquire); | ||
return 1; | ||
} | ||
return 0; | ||
} | ||
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inline size_t getref(const _Atomic(size_t)* r) | ||
{ | ||
return atomic_load_explicit(r, memory_order_relaxed); | ||
} | ||
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} // namespace | ||
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namespace ctl { | ||
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namespace __ { | ||
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void | ||
shared_control::add_shared() noexcept | ||
{ | ||
incref(&shared); | ||
} | ||
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void | ||
shared_control::release_shared() noexcept | ||
{ | ||
if (decref(&shared)) { | ||
on_zero_shared(); | ||
release_weak(); | ||
} | ||
} | ||
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void | ||
shared_control::add_weak() noexcept | ||
{ | ||
incref(&weak); | ||
} | ||
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void | ||
shared_control::release_weak() noexcept | ||
{ | ||
if (decref(&weak)) | ||
on_zero_weak(); | ||
} | ||
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size_t | ||
shared_control::use_count() const noexcept | ||
{ | ||
return 1 + getref(&shared); | ||
} | ||
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size_t | ||
shared_control::weak_count() const noexcept | ||
{ | ||
return getref(&weak); | ||
} | ||
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} // namespace __ | ||
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} // namespace ctl |
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// -*-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 COSMOPOLITAN_CTL_SHARED_PTR_H_ | ||
#define COSMOPOLITAN_CTL_SHARED_PTR_H_ | ||
#include "unique_ptr.h" | ||
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namespace ctl { | ||
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// TODO(mrdomino): move | ||
struct exception | ||
{ | ||
virtual const char* what() const noexcept | ||
{ | ||
return "exception"; | ||
} | ||
}; | ||
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namespace __ { | ||
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struct shared_control | ||
{ | ||
_Atomic(size_t) shared; | ||
_Atomic(size_t) weak; | ||
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constexpr shared_control() noexcept : shared(0), weak(0) | ||
{ | ||
} | ||
virtual ~shared_control() | ||
{ | ||
} | ||
void add_shared() noexcept; | ||
void release_shared() noexcept; | ||
void add_weak() noexcept; | ||
void release_weak() noexcept; | ||
size_t use_count() const noexcept; | ||
size_t weak_count() const noexcept; | ||
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private: | ||
virtual void on_zero_shared() noexcept = 0; | ||
virtual void on_zero_weak() noexcept = 0; | ||
}; | ||
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template<typename T> | ||
struct shared_pointer : shared_control | ||
{ | ||
T* p; | ||
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static shared_pointer* make(T* p) | ||
{ | ||
return new shared_pointer(p); | ||
} | ||
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private: | ||
shared_pointer(T* p) noexcept : p(p) | ||
{ | ||
} | ||
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void on_zero_shared() noexcept override | ||
{ | ||
delete p; | ||
} | ||
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void on_zero_weak() noexcept override | ||
{ | ||
delete this; | ||
} | ||
}; | ||
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} // namespace __ | ||
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struct bad_weak_ptr : ctl::exception | ||
{ | ||
const char* what() const noexcept override | ||
{ | ||
return "bad_weak_ptr"; | ||
} | ||
}; | ||
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template<typename T> | ||
class shared_ptr | ||
{ | ||
public: | ||
constexpr shared_ptr(nullptr_t = nullptr) noexcept | ||
: p(nullptr), ctl(nullptr) | ||
{ | ||
} | ||
shared_ptr(T* const p2) | ||
{ | ||
auto hold = ctl::unique_ptr(p2); | ||
ctl = __::shared_pointer<T>::make(p2); | ||
p = hold.release(); | ||
} | ||
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~shared_ptr() | ||
{ | ||
if (ctl) | ||
ctl->release_shared(); | ||
} | ||
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private: | ||
T* p; | ||
__::shared_control* ctl; | ||
}; | ||
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} // namespace ctl | ||
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#endif // COSMOPOLITAN_CTL_SHARED_PTR_H_ |
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// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*- | ||
// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi | ||
// | ||
// Copyright 2024 Justine Alexandra Roberts Tunney | ||
// | ||
// Permission to use, copy, modify, and/or distribute this software for | ||
// any purpose with or without fee is hereby granted, provided that the | ||
// above copyright notice and this permission notice appear in all copies. | ||
// | ||
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL | ||
// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED | ||
// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE | ||
// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL | ||
// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR | ||
// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER | ||
// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR | ||
// PERFORMANCE OF THIS SOFTWARE. | ||
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#include "ctl/shared_ptr.h" | ||
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template<typename T> | ||
using Ptr = ctl::shared_ptr<T>; | ||
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int | ||
main() | ||
{ | ||
{ | ||
Ptr<int> x; | ||
} | ||
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{ | ||
Ptr<int> x(new int()); | ||
} | ||
return 0; | ||
} |