mirror of
https://github.com/matrix-construct/construct
synced 2024-12-29 17:04:03 +01:00
265 lines
7 KiB
C++
265 lines
7 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_CTX_PROMISE_H
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namespace ircd::ctx
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{
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struct promise_base;
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template<class T = void> class promise;
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template<> class promise<void>;
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IRCD_EXCEPTION(future_error, no_state)
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IRCD_EXCEPTION(future_error, broken_promise)
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IRCD_EXCEPTION(future_error, promise_already_satisfied)
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}
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/// Abstract base type for ctx::promise. This dedupes most of the promissory
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/// functionality with non-template definitions residing in ctx.cc.
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///
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/// In this system the promise is lightweight and maintains a pointer to the
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/// shared_state object which generally resides within the future instance.
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/// If the shared_state object moves or is destroyed the promise's pointer to
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/// it must be updated. The shared_state object also has a pointer to the
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/// promise; if the promise moves or is destroyed that pointer must be updated
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/// as well. This is how the bi-directional relationship is maintained.
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///
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/// To further complicate things, this promise maintains a second pointer
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/// to another instance of a promise implementing a linked-list semantic. All
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/// of these promises are making the same promise to the same shared_state;
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/// the list allows for copy semantics which are important for some callback
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/// systems (like boost::asio). This solution is far more optimal than
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/// allocating the promise in a shared_ptr and refcounting... Note that the
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/// same semantic exists on the future side to implement shared futures. Both
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/// parties maintain a pointer to the head of a singly linked list of the
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/// other party, and a pointer to the next instance of their own party.
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struct ircd::ctx::promise_base
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{
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static const promise_base *head(const shared_state_base &);
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static const promise_base *head(const promise_base &);
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static size_t refcount(const shared_state_base &);
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static size_t refcount(const promise_base &);
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static promise_base *head(shared_state_base &);
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static promise_base *head(promise_base &);
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shared_state_base *st {nullptr}; // the head of all sharing futures
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promise_base *next {nullptr}; // next sharing promise
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template<class T> const shared_state<T> &state() const noexcept;
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template<class T> shared_state<T> &state() noexcept;
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const shared_state_base &state() const noexcept;
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shared_state_base &state() noexcept;
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void check_pending() const;
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void make_ready();
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void remove();
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public:
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bool valid() const noexcept;
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bool operator!() const noexcept;
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explicit operator bool() const noexcept;
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void set_exception(std::exception_ptr);
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protected:
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promise_base() = default;
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promise_base(const promise_base &);
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promise_base(promise_base &&) noexcept;
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promise_base &operator=(const promise_base &);
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promise_base &operator=(promise_base &&) noexcept;
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~promise_base() noexcept;
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};
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/// Value-oriented promise. The user creates an instance of this promise in
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/// order to send a value to a future. After creating an instance of this
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/// promise the user should construct a future with the matching template type
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/// from this. The two will then be linked.
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///
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/// Space for the value will reside within the future instance and not the
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/// promise instance. When the value is set it will be copied (or movied) there.
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///
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/// Full object semantics for this promise are supported; including copy
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/// semantics. All copies of a promise are making the same promise thus
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/// setting a value or exception for one invalidates all the copies.
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///
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/// Instances of this promise can safely destruct at any time. When all copies
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/// of a promise destruct without setting a value or exception the future is
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/// notified with a broken_promise exception.
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template<class T>
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struct ircd::ctx::promise
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:promise_base
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{
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using value_type = typename shared_state<T>::value_type;
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using pointer_type = typename shared_state<T>::pointer_type;
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using reference_type = typename shared_state<T>::reference_type;
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const shared_state<T> &state() const;
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shared_state<T> &state();
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public:
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void set_value(const T &val);
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void set_value(T&& val);
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using promise_base::promise_base;
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using promise_base::operator=;
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};
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/// Valueless promise. The user creates an instance of this promise in
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/// order to notify a future of a success or set an exception for failure.
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///
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/// See docs for promise<T> for more information.
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template<>
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struct ircd::ctx::promise<void>
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:promise_base
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{
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using value_type = typename shared_state<void>::value_type;
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const shared_state<void> &state() const;
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shared_state<void> &state();
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public:
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void set_value();
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using promise_base::promise_base;
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using promise_base::operator=;
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};
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//
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// promise<T>
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//
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template<class T>
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inline void
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ircd::ctx::promise<T>::set_value(T&& val)
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{
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if(!valid())
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return;
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check_pending();
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auto *state
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{
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shared_state_base::head(*this)
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};
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assert(state);
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if(shared_state_base::refcount(*state) > 1) do
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{
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assert(is(*state, future_state::PENDING));
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static_cast<shared_state<T> &>(*state).val = val;
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}
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while((state = state->next)); else
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{
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assert(is(this->state(), future_state::PENDING));
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this->state().val = std::move(val);
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}
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make_ready();
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}
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template<class T>
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inline void
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ircd::ctx::promise<T>::set_value(const T &val)
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{
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if(!valid())
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return;
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check_pending();
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auto *state(shared_state_base::head(*this)); do
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{
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assert(state);
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assert(is(*state, future_state::PENDING));
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static_cast<shared_state<T> &>(*state).val = val;
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}
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while((state = state->next));
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make_ready();
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}
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template<class T>
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inline ircd::ctx::shared_state<T> &
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ircd::ctx::promise<T>::state()
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{
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return promise_base::state<T>();
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}
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template<class T>
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inline const ircd::ctx::shared_state<T> &
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ircd::ctx::promise<T>::state()
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const
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{
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return promise_base::state<T>();
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}
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//
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// promise_base
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//
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inline void
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ircd::ctx::promise_base::check_pending()
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const
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{
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assert(valid());
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if(unlikely(!is(state(), future_state::PENDING)))
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throw promise_already_satisfied{};
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}
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inline bool
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ircd::ctx::promise_base::operator!()
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const noexcept
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{
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return !valid();
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}
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inline ircd::ctx::promise_base::operator
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bool()
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const noexcept
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{
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return valid();
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}
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inline bool
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ircd::ctx::promise_base::valid()
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const noexcept
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{
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return bool(st);
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}
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template<class T>
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inline ircd::ctx::shared_state<T> &
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ircd::ctx::promise_base::state()
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noexcept
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{
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return static_cast<shared_state<T> &>(state());
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}
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template<class T>
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inline const ircd::ctx::shared_state<T> &
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ircd::ctx::promise_base::state()
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const noexcept
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{
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return static_cast<const shared_state<T> &>(state());
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}
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inline ircd::ctx::shared_state_base &
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ircd::ctx::promise_base::state()
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noexcept
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{
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assert(valid());
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return *st;
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}
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inline const ircd::ctx::shared_state_base &
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ircd::ctx::promise_base::state()
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const noexcept
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{
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assert(valid());
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return *st;
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}
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