[saferecl.rcu.base]

# 32 Concurrency support library [[thread]](./#thread)

## 32.11 Safe reclamation [[saferecl]](saferecl#rcu.base)

### 32.11.2 Read-copy update (RCU) [[saferecl.rcu]](saferecl.rcu#base)

#### 32.11.2.3 Class template rcu_obj_base [saferecl.rcu.base]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L12992)

Objects of type T to be protected by RCU inherit from
a specialization rcu_obj_base<T, D> for some D[.](#1.sentence-1)

namespace std {template<class T, class D = default_delete<T>>class rcu_obj_base {public:void retire(D d = D(), rcu_domain& dom = rcu_default_domain()) noexcept; protected: rcu_obj_base() = default;
 rcu_obj_base(const rcu_obj_base&) = default;
 rcu_obj_base(rcu_obj_base&&) = default;
 rcu_obj_base& operator=(const rcu_obj_base&) = default;
 rcu_obj_base& operator=(rcu_obj_base&&) = default; ~rcu_obj_base() = default; private: D *deleter*; // *exposition only*};}

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13015)

The behavior of a program that adds specializations for rcu_obj_base is undefined[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13019)

T may be an incomplete type[.](#3.sentence-1)

It shall be complete before any member of the resulting specialization ofrcu_obj_base is referenced[.](#3.sentence-2)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13024)

D shall be a
function object type ([[function.objects]](function.objects "22.10 Function objects")) for which,
given a value d of type D and
a value ptr of type T*,
the expression d(ptr) is valid[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13031)

D shall meet the requirements for[*Cpp17DefaultConstructible*](utility.arg.requirements#:Cpp17DefaultConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") and [*Cpp17MoveAssignable*](utility.arg.requirements#:Cpp17MoveAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]")[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13035)

If D is trivially copyable,
all specializations of rcu_obj_base<T, D> are trivially copyable[.](#6.sentence-1)

[🔗](#itemdecl:1)

`void retire(D d = D(), rcu_domain& dom = rcu_default_domain()) noexcept;
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13044)

*Mandates*: T is an rcu-protectable type[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13048)

*Preconditions*: *this is
a base class subobject of an object x of type T[.](#8.sentence-1)

The member function rcu_obj_base<T, D>​::​retire was not invoked on x before[.](#8.sentence-2)

The assignment to *deleter* does not exit via an exception[.](#8.sentence-3)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13056)

*Effects*: Evaluates *deleter* = std​::​move(d) and
schedules the evaluation of
the expression *deleter*(  
addressof(x)) in the domain dom;
the behavior is undefined if that evaluation exits via an exception[.](#9.sentence-1)

May invoke scheduled evaluations in dom[.](#9.sentence-2)

[*Note [1](#note-1)*:

If such evaluations acquire resources held across any invocation ofretire on dom, deadlock can occur[.](#9.sentence-3)

— *end note*]