144 lines
4.8 KiB
Markdown
144 lines
4.8 KiB
Markdown
# spin-rs
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[](https://crates.io/crates/spin)
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[](https://docs.rs/spin/)
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[](https://travis-ci.org/mvdnes/spin-rs)
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Spin-based synchronization primitives.
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This crate provides [spin-based](https://en.wikipedia.org/wiki/Spinlock)
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versions of the primitives in `std::sync`. Because synchronization is done
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through spinning, the primitives are suitable for use in `no_std` environments.
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Before deciding to use `spin`, we recommend reading
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[this superb blog post](https://matklad.github.io/2020/01/02/spinlocks-considered-harmful.html)
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by [@matklad](https://github.com/matklad/) that discusses the pros and cons of
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spinlocks. If you have access to `std`, it's likely that the primitives in
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`std::sync` will serve you better except in very specific circumstances.
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## Features
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- `Mutex`, `RwLock`, `Once`, `Lazy` and `Barrier` equivalents
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- Support for `no_std` environments
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- [`lock_api`](https://crates.io/crates/lock_api) compatibility
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- Upgradeable `RwLock` guards
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- Guards can be sent and shared between threads
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- Guard leaking
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- Ticket locks
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- Different strategies for dealing with contention
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## Usage
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Include the following under the `[dependencies]` section in your `Cargo.toml` file.
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```toml
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spin = "x.y"
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```
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## Example
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When calling `lock` on a `Mutex` you will get a guard value that provides access
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to the data. When this guard is dropped, the mutex will become available again.
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```rust
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extern crate spin;
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use std::{sync::Arc, thread};
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fn main() {
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let counter = Arc::new(spin::Mutex::new(0));
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let thread = thread::spawn({
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let counter = counter.clone();
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move || {
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for _ in 0..100 {
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*counter.lock() += 1;
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}
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}
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});
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for _ in 0..100 {
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*counter.lock() += 1;
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}
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thread.join().unwrap();
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assert_eq!(*counter.lock(), 200);
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}
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```
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## Feature flags
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The crate comes with a few feature flags that you may wish to use.
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- `mutex` enables the `Mutex` type.
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- `spin_mutex` enables the `SpinMutex` type.
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- `ticket_mutex` enables the `TicketMutex` type.
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- `use_ticket_mutex` switches to a ticket lock for the implementation of `Mutex`. This
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is recommended only on targets for which ordinary spinning locks perform very badly
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because it will change the implementation used by other crates that depend on `spin`.
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- `rwlock` enables the `RwLock` type.
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- `once` enables the `Once` type.
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- `lazy` enables the `Lazy` type.
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- `barrier` enables the `Barrier` type.
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- `lock_api` enables support for [`lock_api`](https://crates.io/crates/lock_api)
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- `std` enables support for thread yielding instead of spinning.
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- `portable_atomic` enables usage of the `portable-atomic` crate
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to support platforms without native atomic operations (Cortex-M0, etc.).
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The `portable_atomic_unsafe_assume_single_core` cfg or `critical-section` feature
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of `portable-atomic` crate must also be set by the final binary crate.
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When using the cfg, this can be done by adapting the following snippet to the `.cargo/config` file:
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```
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[target.<target>]
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rustflags = [ "--cfg", "portable_atomic_unsafe_assume_single_core" ]
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```
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Note that this cfg is unsafe by nature, and enabling it for multicore systems is unsound.
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When using the `critical-section` feature, you need to implement the critical-section
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implementation that sound for your system by implementing an unsafe trait.
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See [the documentation for the `portable-atomic` crate](https://docs.rs/portable-atomic/latest/portable_atomic/#optional-cfg)
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for more information.
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## Remarks
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It is often desirable to have a lock shared between threads. Wrapping the lock in an
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`std::sync::Arc` is route through which this might be achieved.
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Locks provide zero-overhead access to their data when accessed through a mutable
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reference by using their `get_mut` methods.
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The behaviour of these lock is similar to their namesakes in `std::sync`. they
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differ on the following:
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- Locks will not be poisoned in case of failure.
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- Threads will not yield to the OS scheduler when encounter a lock that cannot be
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accessed. Instead, they will 'spin' in a busy loop until the lock becomes available.
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Many of the feature flags listed above are enabled by default. If you're writing a
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library, we recommend disabling those that you don't use to avoid increasing compilation
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time for your crate's users. You can do this like so:
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```
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[dependencies]
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spin = { version = "x.y", default-features = false, features = [...] }
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```
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## Minimum Safe Rust Version (MSRV)
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This crate is guaranteed to compile on a Minimum Safe Rust Version (MSRV) of 1.38.0 and above.
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This version will not be changed without a minor version bump.
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## License
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`spin` is distributed under the MIT License, (See `LICENSE`).
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