# Crossbeam
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This crate provides a set of tools for concurrent programming:
#### Atomics
* [`AtomicCell`], a thread-safe mutable memory location.<sup>(no_std)</sup>
* [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.<sup>(no_std)</sup>
#### Data structures
* [`deque`], work-stealing deques for building task schedulers.
* [`ArrayQueue`], a bounded MPMC queue that allocates a fixed-capacity buffer on construction.
* [`SegQueue`], an unbounded MPMC queue that allocates small buffers, segments, on demand.
#### Memory management
* [`epoch`], an epoch-based garbage collector.<sup>(alloc)</sup>
#### Thread synchronization
* [`channel`], multi-producer multi-consumer channels for message passing.
* [`Parker`], a thread parking primitive.
* [`ShardedLock`], a sharded reader-writer lock with fast concurrent reads.
* [`WaitGroup`], for synchronizing the beginning or end of some computation.
#### Utilities
* [`Backoff`], for exponential backoff in spin loops.<sup>(no_std)</sup>
* [`CachePadded`], for padding and aligning a value to the length of a cache line.<sup>(no_std)</sup>
* [`scope`], for spawning threads that borrow local variables from the stack.
*Features marked with <sup>(no_std)</sup> can be used in `no_std` environments.*<br/>
*Features marked with <sup>(alloc)</sup> can be used in `no_std` environments, but only if `alloc`
and `nightly` are enabled.*
[`AtomicCell`]: https://docs.rs/crossbeam/*/crossbeam/atomic/struct.AtomicCell.html
[`AtomicConsume`]: https://docs.rs/crossbeam/*/crossbeam/atomic/trait.AtomicConsume.html
[`deque`]: https://docs.rs/crossbeam/*/crossbeam/deque/index.html
[`ArrayQueue`]: https://docs.rs/crossbeam/*/crossbeam/queue/struct.ArrayQueue.html
[`SegQueue`]: https://docs.rs/crossbeam/*/crossbeam/queue/struct.SegQueue.html
[`channel`]: https://docs.rs/crossbeam/*/crossbeam/channel/index.html
[`Parker`]: https://docs.rs/crossbeam/*/crossbeam/sync/struct.Parker.html
[`ShardedLock`]: https://docs.rs/crossbeam/*/crossbeam/sync/struct.ShardedLock.html
[`WaitGroup`]: https://docs.rs/crossbeam/*/crossbeam/sync/struct.WaitGroup.html
[`epoch`]: https://docs.rs/crossbeam/*/crossbeam/epoch/index.html
[`Backoff`]: https://docs.rs/crossbeam/*/crossbeam/utils/struct.Backoff.html
[`CachePadded`]: https://docs.rs/crossbeam/*/crossbeam/utils/struct.CachePadded.html
[`scope`]: https://docs.rs/crossbeam/*/crossbeam/fn.scope.html
## Crates
The main `crossbeam` crate just [re-exports](src/lib.rs) tools from
smaller subcrates:
* [`crossbeam-channel`](crossbeam-channel)
provides multi-producer multi-consumer channels for message passing.
* [`crossbeam-deque`](crossbeam-deque)
provides work-stealing deques, which are primarily intended for building task schedulers.
* [`crossbeam-epoch`](crossbeam-epoch)
provides epoch-based garbage collection for building concurrent data structures.
* [`crossbeam-queue`](crossbeam-queue)
provides concurrent queues that can be shared among threads.
* [`crossbeam-utils`](crossbeam-utils)
provides atomics, synchronization primitives, scoped threads, and other utilities.
There is one more experimental subcrate that is not yet included in `crossbeam`:
* [`crossbeam-skiplist`](crossbeam-skiplist)
provides concurrent maps and sets based on lock-free skip lists.
## Usage
Add this to your `Cargo.toml`:
```toml
[dependencies]
crossbeam = "0.7"
```
## Compatibility
Crossbeam supports stable Rust releases going back at least six months,
and every time the minimum supported Rust version is increased, a new minor
version is released. Currently, the minimum supported Rust version is 1.36.
## Contributing
Crossbeam welcomes contribution from everyone in the form of suggestions, bug reports,
pull requests, and feedback. 💛
If you need ideas for contribution, there are several ways to get started:
* Found a bug or have a feature request?
[Submit an issue](https://github.com/crossbeam-rs/crossbeam/issues/new)!
* Issues and PRs labeled with
[feedback wanted](https://github.com/crossbeam-rs/crossbeam/issues?utf8=%E2%9C%93&q=is%3Aopen+sort%3Aupdated-desc+label%3A%22feedback+wanted%22+)
need feedback from users and contributors.
* Issues labeled with
[good first issue](https://github.com/crossbeam-rs/crossbeam/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc+label%3A%22good+first+issue%22)
are relatively easy starter issues.
#### RFCs
We also have the [RFCs](https://github.com/crossbeam-rs/rfcs) repository for more
high-level discussion, which is the place where we brainstorm ideas and propose
substantial changes to Crossbeam.
You are welcome to participate in any open
[issues](https://github.com/crossbeam-rs/rfcs/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc)
or
[pull requests](https://github.com/crossbeam-rs/rfcs/pulls?q=is%3Apr+is%3Aopen+sort%3Aupdated-desc).
#### Learning resources
If you'd like to learn more about concurrency and non-blocking data structures, there's a
list of learning resources in our [wiki](https://github.com/crossbeam-rs/rfcs/wiki),
which includes relevant blog posts, papers, videos, and other similar projects.
Another good place to visit is [merged RFCs](https://github.com/crossbeam-rs/rfcs/tree/master/text).
They contain elaborate descriptions and rationale for features we've introduced to
Crossbeam, but keep in mind that some of the written information is now out of date.
#### Conduct
The Crossbeam project adheres to the
[Rust Code of Conduct](https://github.com/rust-lang/rust/blob/master/CODE_OF_CONDUCT.md).
This describes the minimum behavior expected from all contributors.
## License
Licensed under either of
* Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
Some Crossbeam subcrates have additional licensing notices.
Take a look at other readme files in this repository for more information.
#### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.