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construct/include/ircd/ctx/continuation.h

151 lines
3.9 KiB
C++

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.
#pragma once
#define HAVE_IRCD_CTX_CONTINUATION_H
// This file is not included with the IRCd standard include stack because
// it requires symbols we can't forward declare without boost headers. It
// is part of the <ircd/asio.h> stack which can be included in your
// definition file if necessary.
namespace ircd::ctx
{
struct continuation;
using yield_context = boost::asio::yield_context;
using interruptor = std::function<void (ctx *const &)>;
using predicate = std::function<bool ()>;
}
namespace ircd
{
using ctx::continuation;
}
/// This object must be placed on the stack when the context is yielding (INTERNAL)
///
/// The instance contains references to some callables which must remain valid.
///
/// - predicate (NOT YET USED)
/// A wakeup condition. This should be a simple boolean function which
/// tests whether the context should be woken up. The continuation references
/// this to convey the condition to a scheduler which may test many predicates
/// while contexts are asleep and then determine a schedule. This is an
/// alternative to waking up contexts first to test their predicates.
///
/// - interruptor
/// An interruption action. This is called when a context cannot wakeup on its
/// own after receiving an interruption without help from this action. Common
/// use for this is with yields to asio.
///
struct ircd::ctx::continuation
{
static const predicate asio_predicate;
static const predicate true_predicate;
static const predicate false_predicate;
static const interruptor noop_interruptor;
const void *const frame_address;
const void *const return_address;
const interruptor *const intr;
const predicate *const pred;
const size_t uncaught_exceptions;
ctx *const self;
operator const boost::asio::yield_context &() const noexcept;
operator boost::asio::yield_context &() noexcept;
void enter();
void leave() noexcept;
template<class yield_closure>
continuation(const predicate &,
const interruptor &,
yield_closure&&);
continuation(continuation &&) = delete;
continuation(const continuation &) = delete;
continuation &operator=(continuation &&) = delete;
continuation &operator=(const continuation &) = delete;
};
template<class yield_closure>
inline
__attribute__((always_inline))
ircd::ctx::continuation::continuation(const predicate &pred,
const interruptor &intr,
yield_closure&& closure)
:frame_address
{
__builtin_frame_address(0)
}
,return_address
{
__builtin_return_address(0)
}
,intr
{
&intr
}
,pred
{
&pred
}
,uncaught_exceptions
{
exception_handler::uncaught_exceptions(0)
}
,self
{
ircd::ctx::current
}
{
// Run the provided routine which performs the actual context switch.
// Everything happening in this closure is no longer considered part
// of this context, but it is technically operating on this stack.
leave();
std::exception_ptr eptr; try
{
closure(static_cast<yield_context &>(*this));
}
catch(...)
{
eptr = std::current_exception();
}
enter();
if(unlikely(eptr))
std::rethrow_exception(eptr);
}
inline void *
__attribute__((always_inline))
boost::coroutines::detail::coroutine_context::jump(coroutine_context &other,
void *param)
{
data_t data
{
this, param
};
context::detail::transfer_t t
{
context::detail::jump_fcontext(other.ctx_, &data)
};
data_t *const td
{
static_cast<data_t *>(t.data)
};
td->from->ctx_ = t.fctx;
return td->data;
}