mirror of
https://github.com/matrix-construct/construct
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96 lines
3.5 KiB
C++
96 lines
3.5 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_CONTINUATION_H
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// This file is not included with the IRCd standard include stack because
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// it requires symbols we can't forward declare without boost headers. It
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// is part of the <ircd/asio.h> stack which can be included in your
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// definition file if necessary.
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namespace ircd::ctx
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{
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struct continuation;
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struct to_asio;
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using yield_context = boost::asio::yield_context;
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using interruptor = std::function<void (ctx *const &) noexcept>;
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using predicate = std::function<bool ()>;
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}
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namespace ircd
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{
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using ctx::yield_context;
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using ctx::continuation;
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using ctx::to_asio;
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}
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/// This object must be placed on the stack when the context is yielding (INTERNAL)
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///
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/// The continuation constructor is the last thing executed before a context
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/// yields. The continuation destructor is the first thing executed when a
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/// context continues. This is not placed by a normal user wishing to context
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/// switch, only a low-level library creator actually implementing the context
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/// switch itself. The placement of this object must be correct. Generally,
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/// we construct the `continuation` as an argument to `yield_context` as such
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/// `yield_context{continuation{}}`. This ensures the continuation destructor
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/// executes before control continues beyond the yield_context call itself and
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/// ties this sequence together neatly.
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///
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/// The instance contains references to some callables which must remain valid.
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///
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/// - predicate (NOT YET USED)
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/// A wakeup condition. This should be a simple boolean function which
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/// tests whether the context should be woken up. The continuation references
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/// this to convey the condition to a scheduler which may test many predicates
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/// while contexts are asleep and then determine a schedule. This is an
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/// alternative to waking up contexts first to test their predicates.
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///
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/// - interruptor
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/// An interruption action. This is called when a context cannot wakeup on its
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/// own after receiving an interruption without help from this action. Common
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/// use for this is with yields to asio.
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///
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struct ircd::ctx::continuation
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{
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static const predicate true_predicate;
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static const predicate false_predicate;
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static const interruptor noop_interruptor;
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ctx *self;
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const predicate &pred;
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const interruptor &intr;
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operator const boost::asio::yield_context &() const;
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operator boost::asio::yield_context &();
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continuation(const predicate & = true_predicate,
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const interruptor & = noop_interruptor);
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~continuation() noexcept(false);
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};
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/// This type of continuation should be used when yielding a context to a
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/// boost::asio handler so we can have specific control over that type of
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/// context switch in possible contrast or extension of the regular
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/// continuation behavior.
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///
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/// The statement `yield_context{to_asio{}}` can be passed to any boost::asio
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/// callback handler. Those handlers have overloads to accept this, many of
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/// which are not documented.
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///
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struct ircd::ctx::to_asio
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:ircd::ctx::continuation
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{
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to_asio() = default;
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to_asio(const interruptor &);
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~to_asio() noexcept(false) = default;
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};
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