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construct/include/ircd/util/scope_count.h

51 lines
1.3 KiB
C++

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2019 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_SCOPE_COUNT_H
namespace ircd {
inline namespace util
{
template<class T> struct scope_count;
}}
/// Increment a counter when constructed and decrement it when destructed.
/// This takes a runtime reference to that counter. The counter thus maintains
/// the number of reentrances (or entrances across different contexts).
///
template<class T>
struct ircd::util::scope_count
{
T *count {nullptr};
T inc {1};
scope_count(T &count, const T & = 1);
scope_count(const scope_count &) = delete;
scope_count(scope_count &&) noexcept = delete;
~scope_count() noexcept;
};
template<class T>
ircd::util::scope_count<T>::scope_count(T &count,
const T &inc)
:count{&count}
,inc{inc}
{
count += inc;
}
template<class T>
ircd::util::scope_count<T>::~scope_count()
noexcept
{
assert(count);
(*count) -= inc;
}