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construct/include/ircd/util/unwind.h

140 lines
3.4 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_UTIL_UNWIND_H
namespace ircd
{
inline namespace util
{
template<class F> struct unwind;
template<class F> struct unwind_nominal;
template<class F> struct unwind_exceptional;
struct unwind_defer;
struct unwind_nominal_assertion;
struct unwind_exceptional_assertion;
}
}
//
// Fundamental scope-unwind utilities establishing actions during destruction
//
/// Unconditionally executes the provided code when the object goes out of scope.
///
template<class F>
struct ircd::util::unwind
{
const F func;
unwind(F&& func)
:func{std::forward<F>(func)}
{}
unwind(const unwind &) = delete;
unwind &operator=(const unwind &) = delete;
~unwind() noexcept
__attribute__((always_inline))
{
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.
///
template<class F>
struct ircd::util::unwind_nominal
{
const F func;
unwind_nominal(F&& func)
:func{std::forward<F>(func)}
{}
~unwind_nominal() noexcept
__attribute__((always_inline))
{
if(likely(!std::uncaught_exceptions()))
func();
}
unwind_nominal(const unwind_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.
///
template<class F>
struct ircd::util::unwind_exceptional
{
const F func;
unwind_exceptional(F&& func)
:func{std::forward<F>(func)}
{}
~unwind_exceptional() noexcept
__attribute__((always_inline))
{
if(unlikely(std::uncaught_exceptions()))
func();
}
unwind_exceptional(const unwind_exceptional &) = delete;
};
/// Posts function to the event loop at the unwind rather than executing it
/// as with nominal/exceptional.
///
struct ircd::util::unwind_defer
{
std::function<void ()> func;
template<class F>
unwind_defer(F&& func)
:func{std::forward<F>(func)}
{}
unwind_defer(const unwind_defer &) = delete;
~unwind_defer() noexcept;
};
/// Asserts that unwind is occurring without any exception. This allows some
/// section of code, for example, the latter half of a function, to assert that
/// it is not throwing and disrupting the other half. This is useful when no
/// exception is expected thus placing other guarantees should not be required
/// if this guarantee is met.
///
struct ircd::util::unwind_nominal_assertion
{
~unwind_nominal_assertion() noexcept
{
assert(likely(!std::uncaught_exceptions()));
}
};
/// Complements exceptional::assertion. This triggers an assertion when
/// unwinding WITHOUT an exception.
///
struct ircd::util::unwind_exceptional_assertion
{
~unwind_exceptional_assertion() noexcept
{
assert(likely(std::uncaught_exceptions()));
}
};