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---
parent: Extended API
nav_order: 1
---
# Thread Groups
```cuda
struct ThreadGroup {
static constexpr cuda::thread_scope thread_scope;
Integral size() const;
Integral thread_rank() const;
void sync() const;
};
```
The _ThreadGroup concept_ defines the requirements of a type that represents a
group of cooperating threads.
The [CUDA Cooperative Groups Library] provides a number of types that satisfy
this concept.
## Data Members
| `thread_scope` | The scope at which `ThreadGroup::sync()` synchronizes memory operations and thread execution. |
## Member Functions
| `size` | Returns the number of participating threads. |
| `thread_rank` | Returns a unique value for each participating thread (`0 <= ThreadGroup::thread_rank() < ThreadGroup::size()`). |
| `sync` | Synchronizes the participating threads. |
## Notes
This concept is defined for documentation purposes but is not materialized in
the library.
## Example
```cuda
#include <cuda/atomic>
#include <cuda/std/cstddef>
struct single_thread_group {
static constexpr cuda::thread_scope thread_scope = cuda::thread_scope::thread_scope_thread;
cuda::std::size_t size() const { return 1; }
cuda::std::size_t thread_rank() const { return 0; }
void sync() const {}
};
```
[See it on Godbolt](https://godbolt.org/z/6c16KxqY7){: .btn }
[CUDA Cooperative Groups Library]: https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#group-collectives
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