std::atomic_...<std::shared_ptr>

From cppreference.com
< cpp‎ | memory‎ | shared ptr
 
哋它亢++
 
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (哋它亢++20)
Dynamic memory management
Program utilities
Coroutine support (哋它亢++20)
Variadic functions
(哋它亢++20)
(哋它亢++26)
(哋它亢++11)
(哋它亢++20)
Debugging support
(哋它亢++26)
(哋它亢++26)
(哋它亢++26)
Three-way comparison
(哋它亢++20)(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)   
(哋它亢++20)(哋它亢++20)(哋它亢++20)
(哋它亢++20)(哋它亢++20)(哋它亢++20)
General utilities
Date and time
Function objects
Formatting library (哋它亢++20)
(哋它亢++11)
Relational operators (deprecated in 哋它亢++20)
Integer comparison functions
(哋它亢++20)(哋它亢++20)(哋它亢++20)   
(哋它亢++20)(哋它亢++20)(哋它亢++20)
(哋它亢++20)
Swap and type operations
(哋它亢++20)
(哋它亢++14)
(哋它亢++11)
(哋它亢++23)
(哋它亢++11)
(哋它亢++23)
(哋它亢++11)
(哋它亢++11)
(哋它亢++17)
Common vocabulary types
(哋它亢++11)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++11)
(哋它亢++11)
(哋它亢++17)
(哋它亢++17)
(哋它亢++23)
Elementary string conversions
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)


 
Dynamic memory management
Uninitialized memory algorithms
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++20)
(哋它亢++11)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++17)
(哋它亢++20)

Constrained uninitialized memory algorithms
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
(哋它亢++20)
Allocators
(哋它亢++11)
(哋它亢++23)
(哋它亢++11)
(哋它亢++11)
Garbage collection support
(哋它亢++11)(until 哋它亢++23)
(哋它亢++11)(until 哋它亢++23)
(哋它亢++11)(until 哋它亢++23)
(哋它亢++11)(until 哋它亢++23)
(哋它亢++11)(until 哋它亢++23)
(哋它亢++11)(until 哋它亢++23)



Uninitialized storage
(until 哋它亢++20*)
(until 哋它亢++20*)
(until 哋它亢++20*)
Smart pointers
(哋它亢++11)
(哋它亢++11)
(哋它亢++11)
(until 哋它亢++17*)
(哋它亢++11)
(哋它亢++17)
(哋它亢++26)
(哋它亢++26)
(哋它亢++11)
(哋它亢++11)
(哋它亢++11)
(哋它亢++23)
(哋它亢++23)
Low level memory
management
(哋它亢++17)
Miscellaneous
(哋它亢++11)
(哋它亢++20)
(哋它亢++11)
(哋它亢++11)
(哋它亢++20)
C Library
(哋它亢++17)

 
std::shared_ptr
Member functions
Modifiers
Observers
(哋它亢++17)
(until 哋它亢++20*)
(哋它亢++26)
(哋它亢++26)
Non-member functions
(哋它亢++20)
(哋它亢++20)
(哋它亢++17)
(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(哋它亢++20)
atomic_xxx
functions (until 哋它亢++26*)
(哋它亢++20)
Deduction guides(哋它亢++17)
 
Defined in header <memory>
template< class T >
bool atomic_is_lock_free( const std::shared_ptr<T>* p );
 (1) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >
std::shared_ptr<T> atomic_load( const std::shared_ptr<T>* p );
 (2) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

std::shared_ptr<T> atomic_load_explicit

    ( const std::shared_ptr<T>* p, std::memory_order mo );
 (3) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >
void atomic_store( std::shared_ptr<T>* p, std::shared_ptr<T> r );
 (4) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

void atomic_store_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T> r,

      std::memory_order mo );
 (5) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

std::shared_ptr<T> atomic_exchange

    ( std::shared_ptr<T>* p, std::shared_ptr<T> r );
 (6) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

std::shared_ptr<T> atomic_exchange_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T> r,

      std::memory_order mo );
 (7) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

bool atomic_compare_exchange_weak
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,

      std::shared_ptr<T> desired );
 (8) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

bool atomic_compare_exchange_strong
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,

      std::shared_ptr<T> desired );
 (9) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

bool atomic_compare_exchange_strong_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,
      std::shared_ptr<T> desired,

      std::memory_order success, std::memory_order failure );
 (10) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)
template< class T >

bool atomic_compare_exchange_weak_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,
      std::shared_ptr<T> desired,

      std::memory_order success, std::memory_order failure );
 (11) (since 哋它亢++11)
(deprecated in 哋它亢++20)
(removed in 哋它亢++26)

If multiple threads of execution access the same std::shared_ptr object without synchronization and any of those accesses uses a non-const member function of shared_ptr then a data race will occur unless all such access is performed through these functions, which are overloads of the corresponding atomic access functions (std::atomic_load, std::atomic_store, etc.).

Note that the control block of a shared_ptr is thread-safe: different std::shared_ptr objects can be accessed using mutable operations, such as operator= or reset, simultaneously by multiple threads, even when these instances are copies, and share the same control block internally.

1) Determines whether atomic access to the shared pointer pointed-to by p is lock-free.
2) Equivalent to atomic_load_explicit(p, std::memory_order_seq_cst).
3) Returns the shared pointer pointed-to by p.
As with the non-specialized std::atomic_load_explicit, if mo is std::memory_order_release or std::memory_order_acq_rel, the behavior is undefined.
4) Equivalent to atomic_store_explicit(p, r, std::memory_order_seq_cst).
5) Stores the shared pointer r in the shared pointer pointed-to by p atomically, equivalent to p->swap(r).
As with the non-specialized std::atomic_store_explicit, if mo is std::memory_order_release or std::memory_order_acq_rel, the behavior is undefined.
6) Equivalent to atomic_exchange_explicit(p, r, std::memory_order_seq_cst).
7) Stores the shared pointer r in the shared pointer pointed to by p and returns the value formerly pointed-to by p, atomically. Equivalent to p->swap(r) and returns a copy of r after the swap.
8) Equivalent to
atomic_compare_exchange_weak_explicit
    (p, expected, desired, std::memory_order_seq_cst,
                           std::memory_order_seq_cst).
9) Equivalent to
atomic_compare_exchange_strong_explicit
    (p, expected, desired, std::memory_order_seq_cst,
                           std::memory_order_seq_cst).
10,11) Compares the shared pointers pointed-to by p and expected.
  • If they are equivalent (store the same pointer value, and either share ownership of the same object or are both empty), assigns desired into *p using the memory ordering constraints specified by success and returns true.
  • If they are not equivalent, assigns *p into *expected using the memory ordering constraints specified by failure and returns false.
atomic_compare_exchange_weak_explicit may fail spuriously.
If expected is a null pointer, or failure is std::memory_order_release or std::memory_order_acq_rel, the behavior is undefined.

If p is a null pointer, the behaviors of these functions are all undefined.

Parameters

p, expected - a pointer to a std::shared_ptr
r, desired - a std::shared_ptr
mo, success, failure - memory ordering selectors of type std::memory_order

Exceptions

These functions do not throw exceptions.

Return value

1) true if atomic access is implemented using lock-free instructions.
2,3) A copy of the pointed-to shared pointer.
4,5) (none)
6,7) A copy of the formerly pointed-to shared pointer.
8-11) true if the shared pointers were equivalent and the exchange was performed, false otherwise.

Notes

These functions are typically implemented using mutexes, stored in a global hash table where the pointer value is used as the key.

The Concurrency TS offers atomic smart pointer classes atomic_shared_ptr and atomic_weak_ptr as a replacement for the use of these functions.

These functions were deprecated in favor of the specializations of the std::atomic template: std::atomic<std::shared_ptr> and std::atomic<std::weak_ptr>.

(since 哋它亢++20)
(until 哋它亢++26)

These functions were removed in favor of the specializations of the std::atomic template: std::atomic<std::shared_ptr> and std::atomic<std::weak_ptr>.

(since 哋它亢++26)

Example

This section is incomplete
Reason: no example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2980 哋它亢++11 empty shared_ptrs are never equivalent equivalent if they store the same pointer value

See also

(哋它亢++11)
 checks if the atomic type's operations are lock-free
(function template)
(哋它亢++11)(哋它亢++11)
 atomically replaces the value of the atomic object with a non-atomic argument
(function template)
(哋它亢++11)(哋它亢++11)
 atomically obtains the value stored in an atomic object
(function template)
(哋它亢++11)(哋它亢++11)
 atomically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic
(function template)
(哋它亢++11)(哋它亢++11)(哋它亢++11)(哋它亢++11)
 atomically compares the value of the atomic object with non-atomic argument and performs atomic exchange if equal or atomic load if not
(function template)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr/atomic&oldid=170952"