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use std::future::Future;
use std::pin::Pin;
use std::task::Poll;
use crate::TantivyError;
pub struct FutureResult<T> {
inner: Inner<T>,
}
enum Inner<T> {
FailedBeforeStart(Option<TantivyError>),
InProgress {
receiver: oneshot::Receiver<crate::Result<T>>,
error_msg_if_failure: &'static str,
},
}
impl<T> From<TantivyError> for FutureResult<T> {
fn from(err: TantivyError) -> Self {
FutureResult {
inner: Inner::FailedBeforeStart(Some(err)),
}
}
}
impl<T> FutureResult<T> {
pub(crate) fn create(
error_msg_if_failure: &'static str,
) -> (Self, oneshot::Sender<crate::Result<T>>) {
let (sender, receiver) = oneshot::channel();
let inner: Inner<T> = Inner::InProgress {
receiver,
error_msg_if_failure,
};
(FutureResult { inner }, sender)
}
pub fn wait(self) -> crate::Result<T> {
match self.inner {
Inner::FailedBeforeStart(err) => Err(err.unwrap()),
Inner::InProgress {
receiver,
error_msg_if_failure,
} => receiver.recv().unwrap_or_else(|_| {
Err(crate::TantivyError::SystemError(
error_msg_if_failure.to_string(),
))
}),
}
}
}
impl<T> Future for FutureResult<T> {
type Output = crate::Result<T>;
fn poll(self: Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Self::Output> {
unsafe {
match &mut Pin::get_unchecked_mut(self).inner {
Inner::FailedBeforeStart(err) => Poll::Ready(Err(err.take().unwrap())),
Inner::InProgress {
receiver,
error_msg_if_failure,
} => match Future::poll(Pin::new_unchecked(receiver), cx) {
Poll::Ready(oneshot_res) => {
let res = oneshot_res.unwrap_or_else(|_| {
Err(crate::TantivyError::SystemError(
error_msg_if_failure.to_string(),
))
});
Poll::Ready(res)
}
Poll::Pending => Poll::Pending,
},
}
}
}
}
#[cfg(test)]
mod tests {
use futures::executor::block_on;
use super::FutureResult;
use crate::TantivyError;
#[test]
fn test_scheduled_result_failed_to_schedule() {
let scheduled_result: FutureResult<()> = FutureResult::from(TantivyError::Poisoned);
let res = block_on(scheduled_result);
assert!(matches!(res, Err(TantivyError::Poisoned)));
}
#[test]
fn test_scheduled_result_error() {
let (scheduled_result, tx): (FutureResult<()>, _) = FutureResult::create("failed");
drop(tx);
let res = block_on(scheduled_result);
assert!(matches!(res, Err(TantivyError::SystemError(_))));
}
#[test]
fn test_scheduled_result_sent_success() {
let (scheduled_result, tx): (FutureResult<u64>, _) = FutureResult::create("failed");
tx.send(Ok(2u64)).unwrap();
assert_eq!(block_on(scheduled_result).unwrap(), 2u64);
}
#[test]
fn test_scheduled_result_sent_error() {
let (scheduled_result, tx): (FutureResult<u64>, _) = FutureResult::create("failed");
tx.send(Err(TantivyError::Poisoned)).unwrap();
let res = block_on(scheduled_result);
assert!(matches!(res, Err(TantivyError::Poisoned)));
}
}