tag | b2ffe0a8f189b4460aa64c47b1f2a1cc2cfa5254 | |
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tagger | The Android Open Source Project <initial-contribution@android.com> | Fri Feb 03 17:02:20 2023 -0800 |
object | 530236e80bcf30e20abd173da534c20b6bd9792e |
Platform Tools Release 34.0.0 (9560563)
commit | 530236e80bcf30e20abd173da534c20b6bd9792e | [log] [tgz] |
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author | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Wed Feb 01 11:02:44 2023 +0000 |
committer | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Wed Feb 01 11:02:44 2023 +0000 |
tree | 1ec219eebf4a24403ad70290c2a8901e51748e30 | |
parent | e2a50d2931ec686cfc933e3b88d91b7b4ef1dbaa [diff] | |
parent | e3720e6e0a14a9f7975af4704d0c80774cc55650 [diff] |
Snap for 9550355 from e3720e6e0a14a9f7975af4704d0c80774cc55650 to sdk-release Change-Id: I337d971b398ae99a2530d9a8a8067d11b5b70f49
Spin-based synchronization primitives.
This crate provides spin-based versions of the primitives in std::sync
. Because synchronization is done through spinning, the primitives are suitable for use in no_std
environments.
Before deciding to use spin
, we recommend reading this superb blog post by @matklad that discusses the pros and cons of spinlocks. If you have access to std
, it's likely that the primitives in std::sync
will serve you better except in very specific circumstances.
Mutex
, RwLock
, Once
, Lazy
and Barrier
equivalentsno_std
environmentslock_api
compatibilityRwLock
guardsInclude the following under the [dependencies]
section in your Cargo.toml
file.
spin = "x.y"
When calling lock
on a Mutex
you will get a guard value that provides access to the data. When this guard is dropped, the mutex will become available again.
extern crate spin; use std::{sync::Arc, thread}; fn main() { let counter = Arc::new(spin::Mutex::new(0)); let thread = thread::spawn({ let counter = counter.clone(); move || { for _ in 0..100 { *counter.lock() += 1; } } }); for _ in 0..100 { *counter.lock() += 1; } thread.join().unwrap(); assert_eq!(*counter.lock(), 200); }
The crate comes with a few feature flags that you may wish to use.
mutex
enables the Mutex
type.
spin_mutex
enables the SpinMutex
type.
ticket_mutex
enables the TicketMutex
type.
use_ticket_mutex
switches to a ticket lock for the implementation of Mutex
. This is recommended only on targets for which ordinary spinning locks perform very badly because it will change the implementation used by other crates that depend on spin
.
rwlock
enables the RwLock
type.
once
enables the Once
type.
lazy
enables the Lazy
type.
barrier
enables the Barrier
type.
lock_api
enables support for lock_api
std
enables support for thread yielding instead of spinning.
portable_atomic
enables usage of the portable-atomic
crate to support platforms without native atomic operations (Cortex-M0, etc.). The portable_atomic_unsafe_assume_single_core
cfg flag must also be set by the final binary crate. This can be done by adapting the following snippet to the .cargo/config
file:
[target.<target>] rustflags = [ "--cfg", "portable_atomic_unsafe_assume_single_core" ]
Note that this cfg is unsafe by nature, and enabling it for multicore systems is unsound.
It is often desirable to have a lock shared between threads. Wrapping the lock in an std::sync::Arc
is route through which this might be achieved.
Locks provide zero-overhead access to their data when accessed through a mutable reference by using their get_mut
methods.
The behaviour of these lock is similar to their namesakes in std::sync
. they differ on the following:
Many of the feature flags listed above are enabled by default. If you‘re writing a library, we recommend disabling those that you don’t use to avoid increasing compilation time for your crate's users. You can do this like so:
[dependencies] spin = { version = "x.y", default-features = false, features = [...] }
spin
is distributed under the MIT License, (See LICENSE
).