# Crossbeam: support for concurrent programming
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Crossbeam supports concurrent programming, especially focusing on memory
management, synchronization, and non-blocking data structures.
Crossbeam consists of several submodules:
- `atomic` for **enhancing `std::sync` API**. `AtomicConsume` provides
C/C++11-style "consume" atomic operations (re-exported from
[`crossbeam-utils`]). `ArcCell` provides atomic storage and retrieval of
`Arc`.
- `utils` and `thread` for **utilities**, re-exported from [`crossbeam-utils`].
The "scoped" thread API in `thread` makes it possible to spawn threads that
share stack data with their parents. The `utils::CachePadded` struct inserts
padding to align data with the size of a cacheline. This crate also seeks to
expand the standard library's few synchronization primitives (locks,
barriers, etc) to include advanced/niche primitives, as well as userspace
alternatives.
- `epoch` for **memory management**, re-exported from [`crossbeam-epoch`].
Because non-blocking data structures avoid global synchronization, it is not
easy to tell when internal data can be safely freed. The crate provides
generic, easy to use, and high-performance APIs for managing memory in these
cases. We plan to support other memory management schemes, e.g. hazard
pointers (HP) and quiescent state-based reclamation (QSBR).
- **Concurrent data structures** which are non-blocking and much superior to
wrapping sequential ones with a `Mutex`. Crossbeam currently provides
channels (re-exported from [`crossbeam-channel`]), deques
(re-exported from [`crossbeam-deque`]), queues, and stacks. Ultimately the
goal is to also include bags, sets and maps.
# Usage
To use Crossbeam, add this to your `Cargo.toml`:
```toml
[dependencies]
crossbeam = "0.4"
```
For examples of what Crossbeam is capable of, see the [documentation][docs].
[docs]: https://docs.rs/crossbeam/
[`crossbeam-epoch`]: https://github.com/crossbeam-rs/crossbeam-epoch
[`crossbeam-utils`]: https://github.com/crossbeam-rs/crossbeam-utils
[`crossbeam-channel`]: https://github.com/crossbeam-rs/crossbeam-channel
[`crossbeam-deque`]: https://github.com/crossbeam-rs/crossbeam-deque