cuda::atomic

Defined in header <cuda/atomic>:

template <typename T, cuda::thread_scope Scope = cuda::thread_scope_system>
class cuda::atomic;

The class template cuda::atomic is an extended form of cuda::std::atomic that takes an additional cuda::thread_scope argument, defaulted to cuda::std::thread_scope_system.

It has the same interface and semantics as cuda::std::atomic, with the following additional operations.

cuda::atomic_thread_fence	Memory order and scope dependent fence synchronization primitive.
cuda::atomic::fetch_min	Atomically find the minimum of the stored value and a provided value.
cuda::atomic::fetch_max	Atomically find the maximum of the stored value and a provided value.

Concurrency Restrictions

An object of type cuda::atomic or cuda::std::atomic shall not be accessed concurrently by CPU and GPU threads unless:

it is in unified memory and the concurrentManagedAccess property is 1, or

it is in CPU memory and the hostNativeAtomicSupported property is 1.

Note, for objects of scopes other than cuda::thread_scope_system this is a data-race, and thefore also prohibited regardless of memory characteristics.

Under CUDA Compute Capability 6 (Pascal), an object of type atomic may not be used:

with automatic storage duration, or

if is_always_lock_free() is false.

Under CUDA Compute Capability prior to 6 (Pascal), objects of type cuda::atomic or cuda::std::atomic may not be used.

Implementation-Defined Behavior

For each type T and cuda::thread_scope S, the value of cuda::atomic<T, S>::is_always_lock_free() is as follows:

Type `T`	cuda::thread_scope `S`	`cuda::atomic<T, S>::is_always_lock_free()`
Any valid type	Any thread scope	`sizeof(T) <= 8`

Example

#include <cuda/atomic>

__global__ void example_kernel() {
  // This atomic is suitable for all threads in the system.
  cuda::atomic<int, cuda::thread_scope_system> a;

  // This atomic has the same type as the previous one (`a`).
  cuda::atomic<int> b;

  // This atomic is suitable for all threads on the current processor (e.g. GPU).
  cuda::atomic<int, cuda::thread_scope_device> c;

  // This atomic is suitable for threads in the same thread block.
  cuda::atomic<int, cuda::thread_scope_block> d;
}

See it on Godbolt