Add a better error message for #39364

There is a known bug in the implementation of mpsc channels in rust.
This adds a clearer error message when the bug occurs, so that developers don't lose too much time looking for the origin of the bug.
See https://github.com/rust-lang/rust/issues/39364

diff --git a/library/std/src/sync/mpsc/shared.rs b/library/std/src/sync/mpsc/shared.rs
index 0c32e636a563357ce39cac0f6313c422b4915c1c..d4ee1b414d9b0faaa938a4dbc64d9c3f8ee325a5 100644 (file)
--- a/library/std/src/sync/mpsc/shared.rs
+++ b/library/std/src/sync/mpsc/shared.rs
@@ -248,7 +248,7 @@ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure> {
     // Returns true if blocking should proceed.
     fn decrement(&self, token: SignalToken) -> StartResult {
         unsafe {
-            assert_eq!(self.to_wake.load(Ordering::SeqCst), 0);
+            assert_eq!(self.to_wake.load(Ordering::SeqCst), 0, "This is a known bug in rust. See https://github.com/rust-lang/rust/issues/39364");
             let ptr = token.cast_to_usize();
             self.to_wake.store(ptr, Ordering::SeqCst);