mirror of
https://github.com/matrix-construct/construct
synced 2024-11-17 23:40:57 +01:00
93 lines
3.1 KiB
C++
93 lines
3.1 KiB
C++
/*
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* Copyright (C) 2016 Charybdis Development Team
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* Copyright (C) 2016 Jason Volk <jason@zemos.net>
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice is present in all copies.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
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* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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* IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#define HAVE_IRCD_LIFE_GUARD_H
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#ifdef __cplusplus
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namespace ircd {
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// Tests if type inherits from std::enable_shared_from_this<>
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template<class T>
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constexpr typename std::enable_if<is_complete<T>::value, bool>::type
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is_shared_from_this()
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{
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return std::is_base_of<std::enable_shared_from_this<T>, T>();
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}
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// Unconditional failure for fwd-declared incomplete types, which
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// obviously don't inherit from std::enable_shared_from_this<>
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template<class T>
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constexpr typename std::enable_if<!is_complete<T>::value, bool>::type
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is_shared_from_this()
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{
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return false;
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}
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/* Use the life_guard to keep an object alive within a function running in a context.
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*
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* Example:
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*
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void foo(client &c)
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{
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const life_guard<client> lg(c);
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c.call(); // This call was always safe with or w/o life_guard.
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ctx::wait(); // The context has now yielded and another context might destroy client &c
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c.call(); // The context continues and this would have made a call on a dead c.
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}
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*/
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template<class T>
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struct life_guard
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:std::shared_ptr<T>
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{
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// This constructor is used when the templated type inherits from std::enable_shared_from_this<>
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template<class SFINAE = T>
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life_guard(T &t,
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typename std::enable_if<is_shared_from_this<SFINAE>(), void>::type * = 0)
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:std::shared_ptr<T>(t.shared_from_this())
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{
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}
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// This constructor uses our convention for forward declaring objects that internally
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// inherit from std::enable_shared_from_this<>. Our convention is to provide:
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//
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// std::shared_ptr<T> shared_from(T &c);
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//
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template<class SFINAE = T>
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life_guard(T &t,
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typename std::enable_if<!is_shared_from_this<SFINAE>(), void>::type * = 0)
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:std::shared_ptr<T>(shared_from(t))
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{
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}
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// This constructor is used with a weak_ptr of the type. This throws an exception
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// to abort the scope when the object already died before being able to guard at all.
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life_guard(const std::weak_ptr<T> &wp)
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:std::shared_ptr<T>(wp.lock())
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{
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if(wp.expired())
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throw std::bad_weak_ptr();
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}
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};
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} // namespace ircd
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#endif // __cplusplus
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