Occasional SIGSEGV (exit code 139) under high concurrency

[sgrebnov]

We have observed occasional crashes when running Vortex under high concurrency. An example stack trace and related discussion can be found here:

• Cayenne acceleration panic in FuturesUnordered::release_task spiceai/spiceai#8830 (comment)

Our conclusion was that the oneshot crate drops stored wakers inside Receiver::drop(). When the waker is an Arc<FuturesUnordered::Task>, this can lead to re-entrant drops, triggering either:

• a safety panic: "future still here when dropping", or
• a SIGSEGV due to a use-after-free.

We fixed this by switching from oneshot to tokio::sync::oneshot. This change resolved the crashes for us, and we have not observed the issue for several weeks since making the switch.

• Use tokio::sync::oneshot to prevent FuturesUnordered reentrant drop crash spiceai/vortex#9

Creating this issue to:

• help others discover this potential problem and its solution, and
• ask whether you would be open to making the same change—using tokio::sync::oneshot when the tokio feature is enabled.