Crossbeam channels trigger valgrind errors

[jdm]

Two examples from https://paste.sh/LwlXNbkD#GFVUcztjTpQbNpZoVKg4SDmI:

==130127== Thread 43 WRRenderBackend#:
==130127== Conditional jump or move depends on uninitialised value(s)
==130127==    at 0x95D09AA: crossbeam_epoch::internal::Global::collect (internal.rs:189)
==130127==    by 0x957E156: crossbeam_epoch::internal::Local::pin (internal.rs:379)
==130127==    by 0x9551625: crossbeam_epoch::collector::LocalHandle::pin (collector.rs:72)
==130127==    by 0x95550E7: crossbeam_epoch::default::pin::{{closure}} (default.rs:23)
==130127==    by 0x9555097: crossbeam_epoch::default::with_handle::{{closure}} (default.rs:42)
==130127==    by 0x955668D: <std::thread::local::LocalKey<T>>::try_with (local.rs:300)
==130127==    by 0x9554F72: crossbeam_epoch::default::with_handle (default.rs:42)
==130127==    by 0x63530B9: crossbeam_epoch::default::pin (default.rs:23)
==130127==    by 0x634717E: <crossbeam_channel::flavors::list::Channel<T>>::start_send (list.rs:161)
==130127==    by 0x6347DB8: <crossbeam_channel::flavors::list::Channel<T>>::send (list.rs:381)
==130127==    by 0x634E381: <crossbeam_channel::channel::Sender<T>>::send (channel.rs:416)
==130127==    by 0x634F347: compositing::compositor_thread::CompositorProxy::send (compositor_thread.rs:31)
==130127== 
==130127== Conditional jump or move depends on uninitialised value(s)
==130127==    at 0x95D4A2F: core::ptr::real_drop_in_place (ptr.rs:193)
==130127==    by 0x95D09D0: crossbeam_epoch::internal::Global::collect (internal.rs:192)
==130127==    by 0x957E156: crossbeam_epoch::internal::Local::pin (internal.rs:379)
==130127==    by 0x9551625: crossbeam_epoch::collector::LocalHandle::pin (collector.rs:72)
==130127==    by 0x95550E7: crossbeam_epoch::default::pin::{{closure}} (default.rs:23)
==130127==    by 0x9555097: crossbeam_epoch::default::with_handle::{{closure}} (default.rs:42)
==130127==    by 0x955668D: <std::thread::local::LocalKey<T>>::try_with (local.rs:300)
==130127==    by 0x9554F72: crossbeam_epoch::default::with_handle (default.rs:42)
==130127==    by 0x63530B9: crossbeam_epoch::default::pin (default.rs:23)
==130127==    by 0x634717E: <crossbeam_channel::flavors::list::Channel<T>>::start_send (list.rs:161)
==130127==    by 0x6347DB8: <crossbeam_channel::flavors::list::Channel<T>>::send (list.rs:381)
==130127==    by 0x634E381: <crossbeam_channel::channel::Sender<T>>::send (channel.rs:416)

@stjepang Have you noticed this happening before?

[ghost]

I haven't noticed this before, thanks for reporting! I'll open an issue in the crossbeam repo and dig into the problem.

To be more precise, looks like the problem is actually in crossbeam-epoch rather than crossbeam-channel. Note that if you update the crossbeam-channel dependency to the latest version, the problem will go away for you since the latest version doesn't use crossbeam-epoch anymore.

[atouchet]

crossbeam-channel was updated in #23288 which removed the crossbeam-epoch 0.6 dependency. Is this fixed now?

[jonhoo]

Alternatively, some unsoundness was also fixed in crossbeam-rs/crossbeam#458, which is about to land on crates.io (in crossbeam-rs/crossbeam#474). Hopefully that should fix this, and if so, we can close crossbeam-rs/crossbeam#347 🎉