Common: Avoid std::function overhead in ScopeGuard

So far in all our uses of ScopeGuard, the type of the callable is
usually just a lambda or a function pointer, so there is no need
to rely on std::function's type erasure.

While the cost of using std::function is probably negligible, it still
causes some unnecessary overhead that can be avoided by making
ScopeGuard a templated class. Thanks to class template argument
deduction in C++17 most existing usages do not even need to be changed.

See https://godbolt.org/z/KcoPni for a comparison between
a ScopeGuard that uses std::function and one that doesn't
This commit is contained in:
Léo Lam
2020-02-15 21:13:29 +01:00
parent 62046d93ce
commit 44b4c2db49
2 changed files with 10 additions and 12 deletions

View File

@ -4,17 +4,15 @@
#pragma once
#include <functional>
#include <optional>
namespace Common
{
template <typename Callable>
class ScopeGuard final
{
public:
template <class Callable>
ScopeGuard(Callable&& finalizer) : m_finalizer(std::forward<Callable>(finalizer))
{
}
ScopeGuard(Callable&& finalizer) : m_finalizer(std::forward<Callable>(finalizer)) {}
ScopeGuard(ScopeGuard&& other) : m_finalizer(std::move(other.m_finalizer))
{
@ -22,13 +20,13 @@ public:
}
~ScopeGuard() { Exit(); }
void Dismiss() { m_finalizer = nullptr; }
void Dismiss() { m_finalizer.reset(); }
void Exit()
{
if (m_finalizer)
{
m_finalizer(); // must not throw
m_finalizer = nullptr;
(*m_finalizer)(); // must not throw
m_finalizer.reset();
}
}
@ -37,7 +35,7 @@ public:
void operator=(const ScopeGuard&) = delete;
private:
std::function<void()> m_finalizer;
std::optional<Callable> m_finalizer;
};
} // Namespace Common