From cff6c4c9277673eca777a04e59e35f8fa00683eb Mon Sep 17 00:00:00 2001 From: Bill Fraser Date: Wed, 23 Feb 2022 04:22:06 -0800 Subject: [PATCH] FuturesUnordered: fix partial iteration (#2574) The IntoIter impl advances the head pointer every iteration, but this breaks the linked list invariant that the head's prev should be null. If the iteration is not done to completion, on subsequent drop, FuturesUnordered::unlink relies on this broken invariant and ends up panicking. The fix is to maintain the `head->prev == null` invariant while iterating. Also added a test for this bug. --- futures-util/src/stream/futures_unordered/iter.rs | 4 ++++ futures/tests/stream_futures_unordered.rs | 14 ++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/futures-util/src/stream/futures_unordered/iter.rs b/futures-util/src/stream/futures_unordered/iter.rs index 04db5ee753..20248c70fe 100644 --- a/futures-util/src/stream/futures_unordered/iter.rs +++ b/futures-util/src/stream/futures_unordered/iter.rs @@ -2,6 +2,7 @@ use super::task::Task; use super::FuturesUnordered; use core::marker::PhantomData; use core::pin::Pin; +use core::ptr; use core::sync::atomic::Ordering::Relaxed; /// Mutable iterator over all futures in the unordered set. @@ -58,6 +59,9 @@ impl Iterator for IntoIter { // valid `next_all` checks can be skipped. let next = (**task).next_all.load(Relaxed); *task = next; + if !task.is_null() { + *(**task).prev_all.get() = ptr::null_mut(); + } self.len -= 1; Some(future) } diff --git a/futures/tests/stream_futures_unordered.rs b/futures/tests/stream_futures_unordered.rs index f62f733610..398170a7cf 100644 --- a/futures/tests/stream_futures_unordered.rs +++ b/futures/tests/stream_futures_unordered.rs @@ -261,6 +261,20 @@ fn into_iter_len() { assert!(into_iter.next().is_none()); } +#[test] +fn into_iter_partial() { + let stream = vec![future::ready(1), future::ready(2), future::ready(3), future::ready(4)] + .into_iter() + .collect::>(); + + let mut into_iter = stream.into_iter(); + assert!(into_iter.next().is_some()); + assert!(into_iter.next().is_some()); + assert!(into_iter.next().is_some()); + assert_eq!(into_iter.len(), 1); + // don't panic when iterator is dropped before completing +} + #[test] fn futures_not_moved_after_poll() { // Future that will be ready after being polled twice,