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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
use std::sync::Arc;
use deno_core::error::AnyError;
use deno_core::futures::future::BoxFuture;
use deno_core::futures::future::LocalBoxFuture;
use deno_core::futures::future::Shared;
use deno_core::futures::FutureExt;
use deno_core::parking_lot::Mutex;
use tokio::task::JoinError;
// todo(dsherret): unit test this
type FutureResult<TResult> = Result<TResult, Arc<AnyError>>;
type JoinResult<TResult> = Result<FutureResult<TResult>, Arc<JoinError>>;
#[derive(Debug)]
struct State<TResult> {
retry_index: usize,
future: Shared<BoxFuture<'static, JoinResult<TResult>>>,
}
/// Attempts to create a shared value asynchronously on one tokio runtime while
/// many runtimes are requesting the value.
///
/// This is only useful when the value needs to get created once across
/// many runtimes.
///
/// This handles the case where one tokio runtime goes down while another
/// one is still running.
#[derive(Debug)]
pub struct MultiRuntimeAsyncValueCreator<TResult: Send + Clone + 'static> {
state: Mutex<State<TResult>>,
}
impl<TResult: Send + Clone + 'static> MultiRuntimeAsyncValueCreator<TResult> {
pub fn new(
future: LocalBoxFuture<'static, Result<TResult, AnyError>>,
) -> Self {
Self {
state: Mutex::new(State {
retry_index: 0,
future: Self::create_shared_future(future),
}),
}
}
pub async fn get(
&self,
recreate_future: impl Fn() -> LocalBoxFuture<'static, Result<TResult, AnyError>>,
) -> Result<TResult, Arc<AnyError>> {
let (mut future, mut retry_index) = {
let state = self.state.lock();
(state.future.clone(), state.retry_index)
};
loop {
let result = future.await;
match result {
Ok(result) => return result,
Err(join_error) => {
if join_error.is_cancelled() {
let mut state = self.state.lock();
if state.retry_index == retry_index {
// we were the first one to retry, so create a new future
// that we'll run from the current runtime
state.retry_index += 1;
state.future = Self::create_shared_future(recreate_future());
}
retry_index = state.retry_index;
future = state.future.clone();
// just in case we're stuck in a loop
if retry_index > 1000 {
panic!("Something went wrong.") // should never happen
}
} else {
panic!("{}", join_error);
}
}
}
}
}
fn create_shared_future(
future: LocalBoxFuture<'static, Result<TResult, AnyError>>,
) -> Shared<BoxFuture<'static, JoinResult<TResult>>> {
deno_core::unsync::spawn(future)
.map(|result| match result {
Ok(Ok(value)) => Ok(Ok(value)),
Ok(Err(err)) => Ok(Err(Arc::new(err))),
Err(err) => Err(Arc::new(err)),
})
.boxed()
.shared()
}
}
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