mirror of
https://github.com/matrix-construct/construct
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118 lines
4.2 KiB
C++
118 lines
4.2 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_SHARED_STATE_H
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namespace ircd::ctx
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{
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enum class future_state :uintptr_t;
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struct shared_state_base;
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struct promise_base;
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template<class T> struct shared_state;
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template<> struct shared_state<void>;
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IRCD_EXCEPTION(ircd::ctx::error, future_error)
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IRCD_OVERLOAD(already)
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future_state state(const shared_state_base &) noexcept;
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bool is(const shared_state_base &, const future_state &) noexcept;
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void set(shared_state_base &, const future_state &);
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}
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/// Internal state enumeration for the promise / future / related. These can
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/// all be observed through state() or is(); only some can be set(). This is
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/// not for public manipulation.
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enum class ircd::ctx::future_state
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:uintptr_t
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{
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INVALID = 0, ///< Null.
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PENDING = 1, ///< Promise is attached and busy.
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READY = 2, ///< Result ready; promise is gone.
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OBSERVED = 3, ///< Special case for when_*(); not a state; promise is gone.
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RETRIEVED = 4, ///< User retrieved future value; promise is gone.
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};
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/// Internal Non-template base of the state object shared by promise and
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/// future. It is extended by the appropriate template, and usually resides
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/// in the future's instance, where the promise finds it.
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///
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/// There can be multiple promises and multiple futures all associated with
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/// the same resolution event. All promises point to the first
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/// shared_state_base (future) of the associated shared_state_base list. When
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/// any promise in the list of associated promises sets a result, it copies
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/// the result to all futures in the list; if only one future, it std::move()'s
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/// the result; then the association of all promises and all futures and
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/// respective lists are invalidated.
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///
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/// Note that the only way to traverse the list of shared_state_bases's is to
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/// dereference the promise pointer (head promise) and follow the st->next
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/// list. The only way to traverse the list of promises is to dereference a
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/// shared_state_base with a valid *p in future_state::PENDING and chase the
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/// p->next list. Each side of the system relies on the other. This means any
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/// proper iteration of the promise or future lists can only take place before
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/// dissolution of the system.
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struct ircd::ctx::shared_state_base
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{
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static const shared_state_base *head(const shared_state_base &);
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static const shared_state_base *head(const promise_base &);
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static size_t refcount(const shared_state_base &);
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static shared_state_base *head(shared_state_base &);
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static shared_state_base *head(promise_base &);
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mutable dock cond;
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std::exception_ptr eptr;
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std::function<void (shared_state_base &)> then;
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shared_state_base *next{nullptr}; // next sharing future
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union alignas(8)
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{
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promise_base *p; // the head of all sharing promises
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future_state st {future_state::INVALID};
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};
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shared_state_base() noexcept;
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shared_state_base(already_t) noexcept;
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shared_state_base(promise_base &);
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shared_state_base(shared_state_base &&) noexcept;
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shared_state_base(const shared_state_base &);
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shared_state_base &operator=(promise_base &);
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shared_state_base &operator=(shared_state_base &&) noexcept;
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shared_state_base &operator=(const shared_state_base &);
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~shared_state_base() noexcept;
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};
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/// Internal shared state between future and promise appropos a future value.
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template<class T>
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struct ircd::ctx::shared_state
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:shared_state_base
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{
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using value_type = T;
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using pointer_type = T *;
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using reference_type = T &;
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T val;
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using shared_state_base::shared_state_base;
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using shared_state_base::operator=;
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};
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/// Internal shared state between future and promise when there is no future
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/// value, only a notification of completion or exception.
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template<>
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struct ircd::ctx::shared_state<void>
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:shared_state_base
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{
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using value_type = void;
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using shared_state_base::shared_state_base;
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using shared_state_base::operator=;
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};
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