18 releases
0.7.0 | Jul 22, 2023 |
---|---|
0.6.0 | Apr 24, 2022 |
0.5.1 | Jan 6, 2022 |
0.4.2 | Jun 10, 2021 |
0.0.0 | Oct 28, 2019 |
#209 in Asynchronous
17,629 downloads per month
Used in 86 crates
(11 directly)
95KB
1.5K
SLoC
async_executors
Abstract over different executors.
async_executors aims to help you write executor agnostic libraries. We express common executor functionality in traits and implement it for the most used executors. This way libraries can require the exact functionality they need and client code can use any executor they choose as long as it can provide the required functionality.
Available traits are grouped in the iface
module. We also implement Spawn
and/or LocalSpawn
traits from futures.
All supported executors are turned on with features, see below.
Table of Contents
Install
With cargo add:
cargo add async_executors
With cargo yaml:
dependencies:
async_executors: ^0.7
With Cargo.toml
[dependencies]
async_executors = "0.7"
Upgrade
Please check out the changelog when upgrading.
Dependencies
This crate has few dependencies. Cargo will automatically handle it's dependencies for you.
The only hard dependencies are futures-task
and futures-util
. The rest are the optional dependencies to turn on support for each executor.
Features
This crate has a lot of features. Lets go over them:
General features
tracing
: when enabled, all traits are re-implemented fortracing-futures::Instrumented
andtracing-futures::WithDispatch
.timer
: Turns on the futures-timer crate. This enables executors to async sleep. On tokio, alternatively you can enabletokio_timer
to enable the tokio native timer. async_std, when not on wasm, provides a timer without needing this feature.
Executor specific:
async_global
: Turns on the executor from async-global-executor. Supports Wasm,!Send
tasks.async_global_tokio
: Makes sure a tokio reactor is running for tasks spawned onAsyncGlobal
.AsyncGlobal
will implement theTokioIo
trait.async_std
: Turns on the executor from the async-std crate. Supports Wasm and!Send
tasks.async_std_tokio
: Makes sure a tokio reactor is running for tasks spawned onAsyncStd
.AsyncStd
will implement theTokioIo
trait.glommio
: Turns on the executor from the glommio crate. Single threaded, Linux 5.8+ only. Supports!Send
tasks.tokio_ct
: Tokio Current thread, enables a single threaded runtime from the tokio crate. Supports!Send
tasks.tokio_tp
: Tokio threadpool, enables a threadpool runtime from the tokio crate.tokio_timer
: Will enable thetime
feature on tokio and callenable_time()
on any tokio runtimes you create. For tokio runtimes, this takes precedence over thetimer
feature.tokio_io
: Will enable thenet
andprocess
features on tokio and callenable_reactor()
on any tokio runtimes you create.TokioCt
andTokioTp
will implement theTokioIo
trait.localpool
: Enables the single threaded executor from futures-executor. Supports!Send
tasks.LocalPool
andLocalSpawner
will be re-exported from this crate and have our traits implemented.threadpool
: Enables the treadpool executor from futures-executor.ThreadPool
will be re-exported from this crate and have our traits implemented.bindgen
: Enables the single threaded executor from wasm-bindgen-futures. Wasm only. Supports!Send
tasks.
Security
The crate itself uses #[ forbid(unsafe_code) ]
.
Our dependencies use unsafe.
Performance
Most wrappers are very thin but the Spawn
and LocalSpawn
traits do imply boxing the future. With executors boxing futures
to put them in a queue you probably get 2 heap allocations per spawn.
JoinHandle
uses the native JoinHandle
types from tokio and async-std to avoid the overhead from RemoteHandle
, but for async-std, wrap the future in Abortable
to create consistent behavior across all executors. The JoinHandle
provided cancels it's future on drop unless you call detach
on it.
SpawnHandle
and LocalSpawnHandle
require boxing the future twice, just like Spawn
and LocalSpawn
.
Existing benchmarks for all executors can be found in executor_benchmarks.
Usage
For API providers
When writing a library that needs to spawn, you probably shouldn't lock your clients into one framework or another. It's usually not appropriate to setup your own thread pool for spawning futures. It belongs to the application developer to decide where futures are spawned and it might not be appreciated if libraries bring in extra dependencies on a framework.
In order to get round this you can take an executor in as a parameter from client code and spawn your futures on the provided executor. Currently the only two traits that are kind of widely available for this are Spawn
and LocalSpawn
from the futures library. Unfortunately, other executor providers do not implement these traits. So by publishing an API that relies on these traits, you would have been restricting the clients to use the executors from futures, or start implementing their own wrappers that implement the traits.
Async_executors has wrappers providing impls on various executors, namely tokio, async_std, wasm_bindgen, ... As such you can just use the trait bounds and refer your users to this crate if they want to use any of the supported executors.
All wrappers also implement Clone
, Debug
and the zero sized ones also Copy
. You can express you will need to clone in your API: impl Spawn + Clone
.
Note that you should never use block_on
inside async contexts. Depending on the executor, this might hang or panic. Some backends we use like tokio and RemoteHandle
from futures use catch_unwind
, so try to keep futures unwind safe.
Spawning with handles
You can use the SpawnHandle
and LocalSpawnHandle
traits as bounds for obtaining join handles.
Example
use
{
async_executors :: { JoinHandle, SpawnHandle, SpawnHandleExt } ,
std :: { sync::Arc } ,
futures :: { FutureExt, executor::{ ThreadPool, block_on } } ,
};
// Example of a library function that needs an executor. Just use impl Trait.
//
fn needs_exec( exec: impl SpawnHandle<()> )
{
let handle = exec.spawn_handle( async {} );
}
// A type that needs to hold on to an executor during it's lifetime. Here it
// must be heap allocated.
//
struct SomeObj{ exec: Arc< dyn SpawnHandle<u8> > }
impl SomeObj
{
pub fn new( exec: Arc< dyn SpawnHandle<u8> > ) -> SomeObj
{
SomeObj{ exec }
}
fn run( &self ) -> JoinHandle<u8>
{
self.exec.spawn_handle( async{ 5 } ).expect( "spawn" )
}
}
fn main()
{
let exec = ThreadPool::new().expect( "build threadpool" );
let obj = SomeObj::new( Arc::new(exec) );
let x = block_on( obj.run() );
assert_eq!( x, 5 );
}
As you can see from the above example, the output of the future is a type parameter on SpawnHandle
. This is necessary because putting it on the method would make the trait no longer object safe, which means it couldn't be stored unless as a type parameter.
The best way to define a combination of abilities you need is by making your own trait alias (here shown with a macro from the trait_set crate, but you can write it out yourself with a blanket implementation if you want):
use async_executors::*;
trait_set::trait_set!
{
pub trait LibExec = SpawnHandle<()> + SpawnHandle<u8> + Timer + YieldNow + Clone;
}
pub fn lib_function( _exec: impl LibExec ) {}
All implementers of SpawnHandle
must support any output type. Thus adding more SpawnHandle
bounds to LibExec
should not be a breaking change.
For API consumers
You can basically pass the wrapper types provided in async_executors to API's that take any of the following. Traits are also implemented for Rc
, Arc
, &
, &mut
, Box
and Instrumented
and WithDispatch
from tracing-futures wrappers:
impl Spawn
impl LocalSpawn
impl SpawnHandle<T>
impl LocalSpawnHandle<T>
impl SpawnBlocking
impl YieldNow
impl Timer
impl TokioIo
All wrappers also implement Clone
, Debug
and the zero sized ones also Copy
.
Some executors are a bit special, so make sure to check the API docs for the one you intend to use. Some also provide extra methods like block_on
which will call a framework specific block_on
rather than the one from futures.
Example
use
{
async_executors :: { AsyncStd, SpawnHandle, TokioTp } ,
std :: { convert::TryFrom } ,
};
fn needs_exec( exec: impl SpawnHandle<()> + SpawnHandle<String> ){};
// AsyncStd is zero sized, so it's easy to instantiate.
//
needs_exec( AsyncStd );
// We need a builder type for tokio, as we guarantee by the type of TokioTp that it
// will be a threadpool.
//
let tp = TokioTp::new().expect( "build threadpool" );
needs_exec( tp );
For more examples, check out the examples directory. If you want to get a more polished API for adhering to structured concurrency, check out async_nursery.
API
API documentation can be found on docs.rs.
Contributing
Please check out the contribution guidelines.
Testing
Run ci/test.bash
and ci/wasm.bash
to run all tests.
Code of conduct
Any of the behaviors described in point 4 "Unacceptable Behavior" of the Citizens Code of Conduct are not welcome here and might get you banned. If anyone including maintainers and moderators of the project fail to respect these/your limits, you are entitled to call them out.
License
Dependencies
~0.9–14MB
~186K SLoC