std::atomic<T>::is_lock_free

 

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Free functions for atomic flags atomic_flag_test_and_setatomic_flag_test_and_set_explicit (C++11)(C++11) atomic_flag_clearatomic_flag_clear_explicit (C++11)(C++11) atomic_flag_testatomic_flag_test_explicit (C++20)(C++20) atomic_flag_waitatomic_flag_wait_explicit (C++20)(C++20) atomic_flag_notify_one (C++20) atomic_flag_notify_all (C++20) Memory ordering memory_order (C++11) kill_dependency (C++11) atomic_thread_fence (C++11) atomic_signal_fence (C++11) Mutual exclusion mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17) timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14) Generic lock management lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11) lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11) Condition variables condition_variable (C++11) condition_variable_any (C++11) notify_all_at_thread_exit (C++11) cv_status (C++11) Semaphores counting_semaphorebinary_semaphore (C++20)(C++20) Latches and barriers latch (C++20) barrier (C++20) Futures promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11) launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

 

std::atomic

Member functions

atomic::atomic

atomic::operator=

atomic::is_lock_free

atomic::store

atomic::load

atomic::operator T

atomic::exchange

atomic::compare_exchange_strongatomic::compare_exchange_weak

atomic::wait (C++20)

atomic::notify_one (C++20)

atomic::notify_all (C++20)

Constants

atomic::is_always_lock_free (C++17)

Specialized member functions

atomic::fetch_add

atomic::fetch_sub

atomic::fetch_and

atomic::fetch_or

atomic::fetch_xor

atomic::operator++atomic::operator++(int)atomic::operator--atomic::operator--(int)

atomic::operator+=atomic::operator-=atomic::operator&=atomic::operator|=atomic::operator^=

 

		(since C++11)
bool is_lock_free() const noexcept;
bool is_lock_free() const volatile noexcept;

Checks whether the atomic operations on all objects of this type are lock-free.

Parameters

(none)

Return value

true if the atomic operations on the objects of this type are lock-free, false otherwise.

Notes

All atomic types except for std::atomic_flag may be implemented using mutexes or other locking operations, rather than using the lock-free atomic CPU instructions. Atomic types are also allowed to be sometimes lock-free, e.g. if only aligned memory accesses are naturally atomic on a given architecture, misaligned objects of the same type have to use locks.

The C++ standard recommends (but does not require) that lock-free atomic operations are also address-free, that is, suitable for communication between processes using shared memory.

Example

Run this code

#include <iostream>
#include <utility>
#include <atomic>
 
struct A { int a[100]; };
struct B { int x, y; };
int main()
{
    std::cout << std::boolalpha
              << "std::atomic<A> is lock free? "
              << std::atomic<A>{}.is_lock_free() << '\n'
              << "std::atomic<B> is lock free? "
              << std::atomic<B>{}.is_lock_free() << '\n';
}

Possible output:

std::atomic<A> is lock free? false
std::atomic<B> is lock free? true

See also

atomic_is_lock_free (C++11)	checks if the atomic type's operations are lock-free (function template)
atomic_is_lock_free(std::shared_ptr)	specializes atomic operations for std::shared_ptr (function template)
is_always_lock_free [static] (C++17)	indicates that the type is always lock-free (public static member constant)