futures_util/future/
catch_unwind.rs

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use std::prelude::v1::*;
use std::any::Any;
use std::panic::{catch_unwind, UnwindSafe, AssertUnwindSafe};

use futures_core::{Future, Poll, Async};
use futures_core::task;

/// Future for the `catch_unwind` combinator.
///
/// This is created by the `Future::catch_unwind` method.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct CatchUnwind<F> where F: Future {
    future: Option<F>,
}

pub fn new<F>(future: F) -> CatchUnwind<F>
    where F: Future + UnwindSafe,
{
    CatchUnwind {
        future: Some(future),
    }
}

impl<F> Future for CatchUnwind<F>
    where F: Future + UnwindSafe,
{
    type Item = Result<F::Item, F::Error>;
    type Error = Box<Any + Send>;

    fn poll(&mut self, cx: &mut task::Context) -> Poll<Self::Item, Self::Error> {
        let mut future = self.future.take().expect("cannot poll twice");
        let (res, future) = catch_unwind(AssertUnwindSafe(|| {
            (future.poll(cx), future)
        }))?;
        match res {
            Ok(Async::Pending) => {
                self.future = Some(future);
                Ok(Async::Pending)
            }
            Ok(Async::Ready(t)) => Ok(Async::Ready(Ok(t))),
            Err(e) => Ok(Async::Ready(Err(e))),
        }
    }
}