madness::atomic_shared_ptr< T > Class Template Reference

#include <atomic_shared_ptr.h>

Public Member Functions
constexpr	atomic_shared_ptr () noexcept=default
	atomic_shared_ptr (atomic_shared_ptr &&other) noexcept
	atomic_shared_ptr (const atomic_shared_ptr &other) noexcept
	Copy-constructs by atomically loading the other pointer.
	atomic_shared_ptr (std::shared_ptr< T > p) noexcept
std::shared_ptr< T >	exchange (std::shared_ptr< T > p={}, std::memory_order order=std::memory_order_seq_cst) noexcept
	operator bool () const noexcept
	operator std::shared_ptr< T > () const noexcept
bool	operator!= (const atomic_shared_ptr &r) const noexcept
const T *	operator-> () const noexcept
T *	operator-> () noexcept
atomic_shared_ptr &	operator= (atomic_shared_ptr &&other) noexcept
atomic_shared_ptr &	operator= (const atomic_shared_ptr &other) noexcept
	Copy-assigns by atomically loading from other and storing.
atomic_shared_ptr &	operator= (std::shared_ptr< T > p) noexcept
	Assigns a new shared_ptr value atomically.
bool	operator== (const atomic_shared_ptr &r) const noexcept
void	reset ()
	Replaces the stored pointer with an empty shared pointer.
void	reset (T *p)
	Replaces the stored pointer, adopting p (may be null).
long	use_count () const noexcept

Private Member Functions
std::shared_ptr< T >	do_load () const noexcept
void	do_store (std::shared_ptr< T > p) noexcept

Private Attributes
std::shared_ptr< T >	ptr_

Detailed Description

template<typename T>
class madness::atomic_shared_ptr< T >

A std::shared_ptr-like handle backed by atomic storage.

Uses std::atomic<std::shared_ptr<T>> when available (C++20), otherwise falls back to the pre-C++20 atomic free functions on std::shared_ptr. The public API mirrors std::shared_ptr (copy construction/assignment, operator->, operator bool, implicit conversion, reset, use_count, equality comparison) plus a single extension, exchange(), needed for the move-optimisation in Future::get()&&.

Note

Move operations are explicitly provided: they atomically take the value from the source (leaving it empty) via a relaxed-order exchange. This is necessary because (a) user-declared copy operations would otherwise suppress the implicit move operations, and (b) std::atomic is non-movable in the C++20 backend, so the implicit move would silently fall back to copy.

All loads/stores and move operations use memory_order_relaxed, relying on the caller to provide necessary ordering guarantees. The exception is exchange(), which defaults to memory_order_seq_cst to match the pre-C++20 std::atomic_exchange behaviour it replaces.

Constructor & Destructor Documentation

atomic_shared_ptr() [1/4]

template<typename T >

constexpr madness::atomic_shared_ptr< T >::atomic_shared_ptr ( )

constexprdefaultnoexcept

atomic_shared_ptr() [2/4]

template<typename T >

madness::atomic_shared_ptr< T >::atomic_shared_ptr ( std::shared_ptr< T >  p )

inlinenoexcept

atomic_shared_ptr() [3/4]

template<typename T >

madness::atomic_shared_ptr< T >::atomic_shared_ptr ( const atomic_shared_ptr< T > &  other )

inlinenoexcept

Copy-constructs by atomically loading the other pointer.

atomic_shared_ptr() [4/4]

template<typename T >

madness::atomic_shared_ptr< T >::atomic_shared_ptr ( atomic_shared_ptr< T > &&  other )

inlinenoexcept

Move-constructs by atomically taking the value from other, which is left empty. Uses memory_order_relaxed (consistent with do_load / do_store); caller is responsible for any synchronization.

Member Function Documentation

do_load()

template<typename T >

std::shared_ptr< T > madness::atomic_shared_ptr< T >::do_load ( ) const

inlineprivatenoexcept

References madness::atomic_shared_ptr< T >::ptr_.

Referenced by madness::atomic_shared_ptr< T >::operator bool(), madness::atomic_shared_ptr< madness::FutureImpl< bool > >::operator std::shared_ptr< madness::FutureImpl< bool > >(), madness::atomic_shared_ptr< T >::operator!=(), madness::atomic_shared_ptr< T >::operator->(), madness::atomic_shared_ptr< T >::operator->(), madness::atomic_shared_ptr< T >::operator==(), and madness::atomic_shared_ptr< T >::use_count().

do_store()

template<typename T >

void madness::atomic_shared_ptr< T >::do_store ( std::shared_ptr< T >  p )

inlineprivatenoexcept

References p(), and madness::atomic_shared_ptr< T >::ptr_.

Referenced by madness::atomic_shared_ptr< T >::operator=(), madness::atomic_shared_ptr< T >::operator=(), madness::atomic_shared_ptr< T >::operator=(), madness::atomic_shared_ptr< T >::reset(), and madness::atomic_shared_ptr< T >::reset().

exchange()

template<typename T >

std::shared_ptr< T > madness::atomic_shared_ptr< T >::exchange ( std::shared_ptr< T >  p = {}, std::memory_order  order = std::memory_order_seq_cst  )

inlinenoexcept

Atomically replaces the stored pointer with p and returns the old value. This is the only operation that differs from std::shared_ptr. Defaults to memory_order_seq_cst to match the pre-C++20 std::atomic_exchange behaviour this replaces.

operator bool()

template<typename T >

madness::atomic_shared_ptr< T >::operator bool ( ) const

inlineexplicitnoexcept

References madness::atomic_shared_ptr< T >::do_load().

operator std::shared_ptr< T >()

template<typename T >

madness::atomic_shared_ptr< T >::operator std::shared_ptr< T > ( ) const

inlinenoexcept

Implicit conversion to shared_ptr, used for lifetime extension and APIs that require a shared_ptr (e.g. RemoteReference).

operator!=()

template<typename T >

bool madness::atomic_shared_ptr< T >::operator!= ( const atomic_shared_ptr< T > &  r ) const

inlinenoexcept

References madness::atomic_shared_ptr< T >::do_load().

operator->() [1/2]

template<typename T >

const T * madness::atomic_shared_ptr< T >::operator-> ( ) const

inlinenoexcept

Dereferences the stored pointer, const overload. Safe because do_load() returns a shared_ptr temporary whose lifetime extends to the end of the full expression containing the -> call, keeping the referent alive across the dereference.

References madness::atomic_shared_ptr< T >::do_load().

operator->() [2/2]

template<typename T >

T * madness::atomic_shared_ptr< T >::operator-> ( )

inlinenoexcept

Dereferences the stored pointer. Safe because do_load() returns a shared_ptr temporary whose lifetime extends to the end of the full expression containing the -> call, keeping the referent alive across the dereference.

References madness::atomic_shared_ptr< T >::do_load().

operator=() [1/3]

template<typename T >

atomic_shared_ptr & madness::atomic_shared_ptr< T >::operator= ( atomic_shared_ptr< T > &&  other )

inlinenoexcept

Move-assigns by atomically taking the value from other, which is left empty. Self-assignment is a no-op.

References madness::atomic_shared_ptr< T >::do_store().

operator=() [2/3]

template<typename T >

atomic_shared_ptr & madness::atomic_shared_ptr< T >::operator= ( const atomic_shared_ptr< T > &  other )

inlinenoexcept

Copy-assigns by atomically loading from other and storing.

References madness::atomic_shared_ptr< T >::do_store().

operator=() [3/3]

template<typename T >

atomic_shared_ptr & madness::atomic_shared_ptr< T >::operator= ( std::shared_ptr< T >  p )

inlinenoexcept

Assigns a new shared_ptr value atomically.

References madness::atomic_shared_ptr< T >::do_store(), and p().

operator==()

template<typename T >

bool madness::atomic_shared_ptr< T >::operator== ( const atomic_shared_ptr< T > &  r ) const

inlinenoexcept

References madness::atomic_shared_ptr< T >::do_load().

reset() [1/2]

template<typename T >

void madness::atomic_shared_ptr< T >::reset ( )

inline

Replaces the stored pointer with an empty shared pointer.

References madness::atomic_shared_ptr< T >::do_store().

reset() [2/2]

template<typename T >

void madness::atomic_shared_ptr< T >::reset ( T *  p )

inline

Replaces the stored pointer, adopting p (may be null).

References madness::atomic_shared_ptr< T >::do_store(), and p().

use_count()

template<typename T >

long madness::atomic_shared_ptr< T >::use_count ( ) const

inlinenoexcept

References madness::atomic_shared_ptr< T >::do_load().

Member Data Documentation

ptr_

template<typename T >

std::shared_ptr<T> madness::atomic_shared_ptr< T >::ptr_

private

Referenced by madness::atomic_shared_ptr< T >::do_load(), and madness::atomic_shared_ptr< T >::do_store().

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The documentation for this class was generated from the following file:

• atomic_shared_ptr.h