NAME¶

std::atomic::is_lock_free - std::atomic::is_lock_free

Synopsis¶

bool is_lock_free() const noexcept; (1) (since C++11)
bool is_lock_free() const volatile noexcept; (2) (since C++11)

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 <atomic>
#include <iostream>
#include <utility>

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