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construct/include/ircd/util/unwind.h

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// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk
//
// 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.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
// INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
// IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
#pragma once
#define HAVE_IRCD_UTIL_UNWIND_H
namespace ircd::util
{
struct unwind;
};
//
// Fundamental scope-unwind utilities establishing actions during destruction
//
/// Unconditionally executes the provided code when the object goes out of scope.
///
struct ircd::util::unwind
{
struct nominal;
struct exceptional;
const std::function<void ()> func;
template<class F>
unwind(F &&func)
:func{std::forward<F>(func)}
{}
unwind(const unwind &) = delete;
unwind &operator=(const unwind &) = delete;
~unwind() noexcept
{
func();
}
};
/// Executes function only if the unwind takes place without active exception
///
/// The function is expected to be executed and the likely() should pipeline
/// that branch and make this device cheaper to use under normal circumstances.
///
struct ircd::util::unwind::nominal
{
const std::function<void ()> func;
template<class F>
nominal(F &&func)
:func{std::forward<F>(func)}
{}
~nominal() noexcept
{
if(likely(!std::uncaught_exception()))
func();
}
nominal(const nominal &) = delete;
};
/// Executes function only if unwind is taking place because exception thrown
///
/// The unlikely() intends for the cost of a branch misprediction to be paid
/// for fetching and executing this function. This is because we strive to
/// optimize the pipeline for the nominal path, making this device as cheap
/// as possible to use.
///
struct ircd::util::unwind::exceptional
{
const std::function<void ()> func;
template<class F>
exceptional(F &&func)
:func{std::forward<F>(func)}
{}
~exceptional() noexcept
{
if(unlikely(std::uncaught_exception()))
func();
}
exceptional(const exceptional &) = delete;
};