mirror of
https://github.com/matrix-construct/construct
synced 2024-08-28 20:35:16 +02:00
148 lines
3.4 KiB
C++
148 lines
3.4 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_VIEW_H
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namespace ircd::ctx
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{
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template<class T> class shared_view;
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}
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/// Device for a context to share data on its stack with others while yielding
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///
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/// The shared_view yields a context while other contexts examine the object pointed
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/// to in the shared_view. This allows a producing context to construct something
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/// on its stack and then wait for the consuming contexts to do something with
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/// that data before the producer resumes and potentially destroys the data.
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/// This creates a very simple and lightweight single-producer/multi-consumer
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/// queue mechanism using only context switching.
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///
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/// The producer is blocked until all consumers are finished with their shared_view.
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/// The consumers acquire the shared_lock before passing it to the call to wait().
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/// wait() returns with a shared_view of the object under shared_lock. Once the
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/// consumer releases the shared_lock the viewed object is not safe for them.
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///
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template<class T>
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class ircd::ctx::shared_view
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:public shared_mutex
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{
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T *t {nullptr};
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dock q;
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size_t waiting {0};
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bool ready() const;
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public:
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// Consumer interface;
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template<class time_point> T &wait_until(std::shared_lock<shared_view> &, time_point&&);
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template<class duration> T &wait_for(std::shared_lock<shared_view> &, const duration &);
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T &wait(std::shared_lock<shared_view> &);
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// Producer interface;
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void notify(T &);
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shared_view() = default;
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~shared_view() noexcept;
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};
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template<class T>
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ircd::ctx::shared_view<T>::~shared_view()
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noexcept
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{
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assert(!waiting);
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}
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template<class T>
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void
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ircd::ctx::shared_view<T>::notify(T &t)
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{
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if(!waiting)
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return;
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this->t = &t;
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q.notify_all();
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q.wait([this] { return !waiting; });
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const std::lock_guard<shared_view> lock{*this};
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this->t = nullptr;
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assert(!waiting);
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q.notify_all();
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}
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template<class T>
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T &
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ircd::ctx::shared_view<T>::wait(std::shared_lock<shared_view> &lock)
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{
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for(assert(lock.owns_lock_shared()); ready(); lock.lock_shared())
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{
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lock.unlock_shared();
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q.wait();
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}
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const unwind ul{[this]
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{
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--waiting;
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q.notify_all();
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}};
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for(++waiting; !ready(); lock.lock_shared())
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{
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lock.unlock_shared();
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q.wait();
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}
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assert(t != nullptr);
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return *t;
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}
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template<class T>
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template<class duration>
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T &
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ircd::ctx::shared_view<T>::wait_for(std::shared_lock<shared_view> &lock,
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const duration &dur)
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{
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return wait_until(now<steady_point>() + dur);
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}
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template<class T>
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template<class time_point>
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T &
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ircd::ctx::shared_view<T>::wait_until(std::shared_lock<shared_view> &lock,
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time_point&& tp)
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{
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for(assert(lock.owns_lock_shared()); ready(); lock.lock_shared())
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{
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lock.unlock_shared();
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q.wait_until(tp);
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}
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const unwind ul{[this]
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{
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--waiting;
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q.notify_all();
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}};
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for(++waiting; !ready(); lock.lock_shared())
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{
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lock.unlock_shared();
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q.wait_until(tp);
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}
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assert(t != nullptr);
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return *t;
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}
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template<class T>
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bool
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ircd::ctx::shared_view<T>::ready()
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const
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{
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return t != nullptr;
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}
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