backoff/future.rs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239
use std::{
future::Future,
pin::Pin,
task::{Context, Poll},
time::Duration,
};
use futures_core::ready;
use pin_project_lite::pin_project;
use crate::{backoff::Backoff, error::Error};
use crate::retry::{NoopNotify, Notify};
pub trait Sleeper {
type Sleep: Future<Output = ()> + Send + 'static;
fn sleep(&self, dur: Duration) -> Self::Sleep;
}
/// Retries given `operation` according to the [`Backoff`] policy
/// [`Backoff`] is reset before it is used.
/// The returned future can be spawned onto a compatible runtime.
///
/// Only available through the `tokio` and `async-std` feature flags.
///
/// # Example
///
/// ```rust
/// use backoff::ExponentialBackoff;
///
/// async fn f() -> Result<(), backoff::Error<&'static str>> {
/// // Business logic...
/// Err(backoff::Error::Permanent("error"))
/// }
///
/// # async fn go() {
/// backoff::future::retry(ExponentialBackoff::default(), f).await.err().unwrap();
/// # }
/// # fn main() { futures_executor::block_on(go()); }
/// ```
#[cfg(any(feature = "tokio", feature = "async-std"))]
pub fn retry<I, E, Fn, Fut, B>(
backoff: B,
operation: Fn,
) -> Retry<impl Sleeper, B, NoopNotify, Fn, Fut>
where
B: Backoff,
Fn: FnMut() -> Fut,
Fut: Future<Output = Result<I, Error<E>>>,
{
retry_notify(backoff, operation, NoopNotify)
}
/// Retries given `operation` according to the [`Backoff`] policy.
/// Calls `notify` on failed attempts (in case of [`Error::Transient`]).
/// [`Backoff`] is reset before it is used.
/// The returned future can be spawned onto a compatible runtime.
///
/// Only available through the `tokio` and `async-std` feature flags.
///
/// # Async `notify`
///
/// `notify` can be neither `async fn` or [`Future`]. If you need to perform some async
/// operations inside `notify`, consider using your runtimes task-spawning functionality.
///
/// The reason behind this is that [`Retry`] future cannot be responsible for polling
/// `notify` future, because can easily be dropped _before_ `notify` is completed.
/// So, considering the fact that most of the time no async operations are required in
/// `notify`, it's up to the caller to decide how async `notify` should be performed.
///
/// # Example
///
/// ```rust
/// use backoff::backoff::Stop;
///
/// async fn f() -> Result<(), backoff::Error<&'static str>> {
/// // Business logic...
/// Err(backoff::Error::transient("error"))
/// }
///
/// # async fn go() {
/// let err = backoff::future::retry_notify(Stop {}, f, |e, dur| {
/// println!("Error happened at {:?}: {}", dur, e)
/// })
/// .await
/// .err()
/// .unwrap();
/// assert_eq!(err, "error");
/// # }
/// # fn main() { futures_executor::block_on(go()); }
/// ```
#[cfg(any(feature = "tokio", feature = "async-std"))]
pub fn retry_notify<I, E, Fn, Fut, B, N>(
mut backoff: B,
operation: Fn,
notify: N,
) -> Retry<impl Sleeper, B, N, Fn, Fut>
where
B: Backoff,
Fn: FnMut() -> Fut,
Fut: Future<Output = Result<I, Error<E>>>,
N: Notify<E>,
{
backoff.reset();
Retry::new(rt_sleeper(), backoff, notify, operation)
}
pin_project! {
/// Retry implementation.
pub struct Retry<S: Sleeper, B, N, Fn, Fut> {
// The [`Sleeper`] that we generate the `delay` futures from.
sleeper: S,
// [`Backoff`] implementation to count next [`Retry::delay`] with.
backoff: B,
// [`Future`] which delays execution before next [`Retry::operation`] invocation.
#[pin]
delay: OptionPinned<S::Sleep>,
// Operation to be retried. It must return [`Future`].
operation: Fn,
// [`Future`] being resolved once [`Retry::operation`] is completed.
#[pin]
fut: Fut,
// [`Notify`] implementation to track [`Retry`] ticks.
notify: N,
}
}
impl<S, B, N, Fn, Fut, I, E> Retry<S, B, N, Fn, Fut>
where
S: Sleeper,
Fn: FnMut() -> Fut,
Fut: Future<Output = Result<I, Error<E>>>,
{
pub fn new(sleeper: S, backoff: B, notify: N, mut operation: Fn) -> Self {
let fut = operation();
Retry {
sleeper,
backoff,
delay: OptionPinned::None,
operation,
fut,
notify,
}
}
}
pin_project! {
#[project = OptionProj]
enum OptionPinned<T> {
Some {
#[pin]
inner: T,
},
None,
}
}
impl<S, B, N, Fn, Fut, I, E> Future for Retry<S, B, N, Fn, Fut>
where
S: Sleeper,
B: Backoff,
N: Notify<E>,
Fn: FnMut() -> Fut,
Fut: Future<Output = Result<I, Error<E>>>,
{
type Output = Result<I, E>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut this = self.project();
loop {
if let OptionProj::Some { inner: delay } = this.delay.as_mut().project() {
ready!(delay.poll(cx));
this.delay.set(OptionPinned::None);
}
match ready!(this.fut.as_mut().poll(cx)) {
Ok(v) => return Poll::Ready(Ok(v)),
Err(Error::Permanent(e)) => return Poll::Ready(Err(e)),
Err(Error::Transient { err, retry_after }) => {
match retry_after.or_else(|| this.backoff.next_backoff()) {
Some(duration) => {
this.notify.notify(err, duration);
this.delay.set(OptionPinned::Some {
inner: this.sleeper.sleep(duration),
});
this.fut.set((this.operation)());
}
None => return Poll::Ready(Err(err)),
}
}
}
}
}
}
#[cfg(all(feature = "tokio", feature = "async-std"))]
compile_error!("Feature \"tokio\" and \"async-std\" cannot be enabled at the same time");
#[cfg(feature = "async-std")]
fn rt_sleeper() -> impl Sleeper {
AsyncStdSleeper
}
#[cfg(feature = "tokio")]
fn rt_sleeper() -> impl Sleeper {
TokioSleeper
}
#[cfg(feature = "tokio")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
struct TokioSleeper;
#[cfg(feature = "tokio")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
impl Sleeper for TokioSleeper {
type Sleep = ::tokio_1::time::Sleep;
fn sleep(&self, dur: Duration) -> Self::Sleep {
::tokio_1::time::sleep(dur)
}
}
#[cfg(feature = "async-std")]
#[cfg_attr(docsrs, doc(cfg(feature = "async-std")))]
struct AsyncStdSleeper;
#[cfg(feature = "async-std")]
#[cfg_attr(docsrs, doc(cfg(feature = "async-std")))]
impl Sleeper for AsyncStdSleeper {
type Sleep = Pin<Box<dyn Future<Output = ()> + Send + 'static>>;
fn sleep(&self, dur: Duration) -> Self::Sleep {
Box::pin(::async_std_1::task::sleep(dur))
}
}