[saferecl.hp.holder.mem]

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

## 32.11 Safe reclamation [[saferecl]](saferecl#hp.holder.mem)

### 32.11.3 Hazard pointers [[saferecl.hp]](saferecl.hp#holder.mem)

#### 32.11.3.4 Class hazard_pointer [[saferecl.hp.holder]](saferecl.hp.holder#mem)

#### 32.11.3.4.3 Member functions [saferecl.hp.holder.mem]

[ð](#lib:empty,hazard_pointer)

`bool empty() const noexcept;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13573)

*Returns*: true if and only if *this is empty[.](#1.sentence-1)

[ð](#lib:protect,hazard_pointer)

`template<class T> T* protect(const atomic<T*>& src) noexcept;
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13584)

*Effects*: Equivalent to:T* ptr = src.load(memory_order::relaxed);while (!try_protect(ptr, src)) {}return ptr;

[ð](#lib:try_protect,hazard_pointer)

`template<class T> bool try_protect(T*& ptr, const atomic<T*>& src) noexcept;
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13600)

*Mandates*: T is a hazard-protectable type[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13604)

*Preconditions*: *this is not empty[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13608)

*Effects*: Performs the following steps in order:

- [(5.1)](#5.1)

  Initializes a variable old of type T* with the value of ptr[.](#5.1.sentence-1)

- [(5.2)](#5.2)

  Evaluates reset_protection(old)[.](#5.2.sentence-1)

- [(5.3)](#5.3)

  Assigns the value of src.load(memory_order​::​acquire) to ptr[.](#5.3.sentence-1)

- [(5.4)](#5.4)

  If old == ptr is false,
evaluates reset_protection()[.](#5.4.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13619)

*Returns*: old == ptr[.](#6.sentence-1)

[ð](#lib:reset_protection,hazard_pointer)

`template<class T> void reset_protection(const T* ptr) noexcept;
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13630)

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

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13634)

*Preconditions*: *this is not empty[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13638)

*Effects*: If ptr is a null pointer value, invokes reset_protection()[.](#9.sentence-1)

Otherwise,
associates the hazard pointer owned by *this with *ptr,
thereby ending the current protection epoch[.](#9.sentence-2)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13645)

*Complexity*: Constant[.](#10.sentence-1)

[ð](#lib:reset_protection,hazard_pointer_)

`void reset_protection(nullptr_t = nullptr) noexcept;
`

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13656)

*Preconditions*: *this is not empty[.](#11.sentence-1)

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13660)

*Postconditions*: The hazard pointer owned by *this is unassociated[.](#12.sentence-1)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13664)

*Complexity*: Constant[.](#13.sentence-1)

[ð](#lib:swap,hazard_pointer)

`void swap(hazard_pointer& other) noexcept;
`

[14](#14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13675)

*Effects*: Swaps the hazard pointer ownership of this object with that of other[.](#14.sentence-1)

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

The owned hazard pointers, if any, remain unchanged during the swap and
continue to be associated with the respective objects
that they were protecting before the swap, if any[.](#14.sentence-2)

No protection epochs are ended or initiated[.](#14.sentence-3)

â *end note*]

[15](#15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L13685)

*Complexity*: Constant[.](#15.sentence-1)
