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use std::{
future::Future,
pin::Pin,
task::{Context, Poll},
};
use crate::{BudgetContext, BudgetContextData, Budgetable, Container};
/// Spends `amount` from the curent budget.
///
/// This is a future that must be awaited. This future is created by `spend()`.
#[derive(Debug)]
#[must_use = "budget is not spent until this future is awaited"]
pub(crate) struct SpendBudget<'a, Backing, Budget>
where
Backing: Container<BudgetContextData<Budget>>,
{
pub(crate) context: &'a BudgetContext<Backing, Budget>,
pub(crate) amount: usize,
}
impl<'a, Backing, Budget> Future for SpendBudget<'a, Backing, Budget>
Budget: Budgetable,
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
self.context.data.map_locked(|data| {
if data.budget.spend(self.amount) {
data.budget.remove_waker(cx.waker());
Poll::Ready(())
} else {
// Not enough budget
match &mut data.paused_future {
Some(existing_waker) if existing_waker.will_wake(cx.waker()) => {
*existing_waker = cx.waker().clone();
waker => {
*waker = Some(cx.waker().clone());
data.budget.add_waker(cx.waker());
Poll::Pending
})
macro_rules! define_public_interface {
($modulename:ident, $backing:ident, $moduledocs:literal) => {
#[doc = $moduledocs]
pub mod $modulename {
use crate::{BudgetContextData, Budgetable};
type Backing<Budget> = crate::$backing<crate::BudgetContextData<Budget>>;
pub struct SpendBudget<'a, Budget>(
crate::SpendBudget<'a, crate::$backing<BudgetContextData<Budget>>, Budget>,
)
Budget: Budgetable;
impl<'a, Budget> Future for SpendBudget<'a, Budget>
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let inner = Pin::new(&mut self.0);
inner.poll(cx)
impl<'a, Budget> From<super::SpendBudget<'a, Backing<Budget>, Budget>>
for SpendBudget<'a, Budget>
fn from(future: super::SpendBudget<'a, Backing<Budget>, Budget>) -> Self {
Self(future)
define_public_interface!(
threadsafe,
SyncContainer,
"Threadsafe (`Send + Sync`) budget spending"
);
singlethreaded,
NotSyncContainer,
"Single-threaded (`!Send + !Sync`) budget spending"