mirror of
https://github.com/matrix-construct/construct
synced 2024-11-27 09:12:36 +01:00
140 lines
3.4 KiB
C++
140 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_UTIL_UNWIND_H
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namespace ircd
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{
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inline namespace util
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{
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template<class F> struct unwind;
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template<class F> struct unwind_nominal;
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template<class F> struct unwind_exceptional;
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struct unwind_defer;
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struct unwind_nominal_assertion;
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struct unwind_exceptional_assertion;
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}
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}
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//
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// Fundamental scope-unwind utilities establishing actions during destruction
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//
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/// Unconditionally executes the provided code when the object goes out of scope.
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///
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template<class F>
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struct ircd::util::unwind
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{
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const F func;
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unwind(F&& func)
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:func{std::forward<F>(func)}
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{}
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unwind(const unwind &) = delete;
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unwind &operator=(const unwind &) = delete;
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~unwind() noexcept
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__attribute__((always_inline))
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{
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func();
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}
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};
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/// Executes function only if the unwind takes place without active exception
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///
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/// The function is expected to be executed and the likely() should pipeline
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/// that branch and make this device cheaper to use under normal circumstances.
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///
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template<class F>
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struct ircd::util::unwind_nominal
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{
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const F func;
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unwind_nominal(F&& func)
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:func{std::forward<F>(func)}
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{}
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~unwind_nominal() noexcept
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__attribute__((always_inline))
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{
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if(likely(!std::uncaught_exceptions()))
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func();
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}
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unwind_nominal(const unwind_nominal &) = delete;
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};
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/// Executes function only if unwind is taking place because exception thrown
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///
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/// The unlikely() intends for the cost of a branch misprediction to be paid
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/// for fetching and executing this function. This is because we strive to
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/// optimize the pipeline for the nominal path, making this device as cheap
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/// as possible to use.
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///
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template<class F>
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struct ircd::util::unwind_exceptional
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{
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const F func;
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unwind_exceptional(F&& func)
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:func{std::forward<F>(func)}
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{}
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~unwind_exceptional() noexcept
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__attribute__((always_inline))
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{
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if(unlikely(std::uncaught_exceptions()))
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func();
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}
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unwind_exceptional(const unwind_exceptional &) = delete;
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};
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/// Posts function to the event loop at the unwind rather than executing it
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/// as with nominal/exceptional.
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///
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struct ircd::util::unwind_defer
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{
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std::function<void ()> func;
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template<class F>
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unwind_defer(F&& func)
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:func{std::forward<F>(func)}
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{}
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unwind_defer(const unwind_defer &) = delete;
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~unwind_defer() noexcept;
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};
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/// Asserts that unwind is occurring without any exception. This allows some
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/// section of code, for example, the latter half of a function, to assert that
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/// it is not throwing and disrupting the other half. This is useful when no
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/// exception is expected thus placing other guarantees should not be required
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/// if this guarantee is met.
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///
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struct ircd::util::unwind_nominal_assertion
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{
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~unwind_nominal_assertion() noexcept
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{
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assert(likely(!std::uncaught_exceptions()));
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}
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};
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/// Complements exceptional::assertion. This triggers an assertion when
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/// unwinding WITHOUT an exception.
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///
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struct ircd::util::unwind_exceptional_assertion
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{
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~unwind_exceptional_assertion() noexcept
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{
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assert(likely(std::uncaught_exceptions()));
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}
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};
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