mirror of
https://github.com/matrix-construct/construct
synced 2024-12-11 08:02:59 +01:00
102 lines
3.1 KiB
C++
102 lines
3.1 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 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. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_UTIL_LIFE_GUARD_H
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namespace ircd::util
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{
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// Convenience functions for types shared_from_this
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template<class T> std::shared_ptr<const T> shared_from(const T &t);
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template<class T> std::shared_ptr<T> shared_from(T &t);
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template<class T> std::weak_ptr<const T> weak_from(const T &t);
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template<class T> std::weak_ptr<T> weak_from(T &t);
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template<class T> struct life_guard;
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}
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/// life_guard is a convenience which takes advantage of std::enable_shared_from_this<T>.
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/// The life_guard glorifies the constructor of an std::shared_ptr<T> by accepting
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/// std::weak_ptr<T> and T& itself all with proper semantics. Once construction is
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/// successful, the user holds it for the duration of the scope ensuring T& survives
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/// context interleaving without being destructed.
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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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///
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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 ircd::util::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>(shared_from(t))
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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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// 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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template<class T>
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std::weak_ptr<T>
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ircd::util::weak_from(T &t)
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{
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return shared_from(t);
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};
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template<class T>
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std::weak_ptr<const T>
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ircd::util::weak_from(const T &t)
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{
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return shared_from(t);
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};
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template<class T>
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std::shared_ptr<T>
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ircd::util::shared_from(T &t)
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{
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return dynamic_pointer_cast<T>(t.shared_from_this());
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};
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template<class T>
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std::shared_ptr<const T>
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ircd::util::shared_from(const T &t)
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{
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return dynamic_pointer_cast<const T>(t.shared_from_this());
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};
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