threads: log every wait and notify (#7220)

When troubleshooting deadlocks in WebAssembly modules, it is important
to understand which `wait` instructions are still pending a `notify`.
It would be nice to have some kind of `--warn-deadlock-after=1s` flag
available that would poll the parking lot for `wait`s hanging past the
time limit, but I realized the real value would be to tie the `wait`
instruction (through CLIF) to the original source code, if debug
information were available. This did not seem to be entirely feasible,
since CLIF loses the original Wasm source context (is this true?) and I
was not confident that we would be able to use `addr2line` to map from
Wasm instructions to source (e.g., see @cfallin's
[issue](gimli-rs/addr2line#265)).

Instead, this change simply logs each valid `wait` and `notify`
execution, leaving it to the user to figure out which one is hanging
(should not be too difficult) and how to map this back to their source
code (more difficult).

crates/runtime/src/memory.rs

@@ -565,6 +565,7 @@ impl SharedMemory {
     /// Implementation of `memory.atomic.notify` for this shared memory.
     pub fn atomic_notify(&self, addr_index: u64, count: u32) -> Result<u32, Trap> {
         validate_atomic_addr(&self.0.def.0, addr_index, 4, 4)?;
+        log::trace!("memory.atomic.notify(addr={addr_index}, count={count})");
         Ok(self.0.spot.unpark(addr_index, count))
     }
 
@@ -576,13 +577,18 @@ impl SharedMemory {
         timeout: Option<Instant>,
     ) -> Result<WaitResult, Trap> {
         let addr = validate_atomic_addr(&self.0.def.0, addr_index, 4, 4)?;
+        log::trace!(
+            "memory.atomic.wait32(addr={addr_index}, expected={expected}, timeout={timeout:?})"
+        );
+
         // SAFETY: `addr_index` was validated by `validate_atomic_addr` above.
         assert!(std::mem::size_of::<AtomicU32>() == 4);
         assert!(std::mem::align_of::<AtomicU32>() <= 4);
         let atomic = unsafe { &*(addr as *const AtomicU32) };
 
-        // We want the sequential consistency of `SeqCst` to ensure that the `load` sees the value that the `notify` will/would see.
-        // All WASM atomic operations are also `SeqCst`.
+        // We want the sequential consistency of `SeqCst` to ensure that the
+        // `load` sees the value that the `notify` will/would see. All WASM
+        // atomic operations are also `SeqCst`.
         let validate = || atomic.load(Ordering::SeqCst) == expected;
 
         Ok(self.0.spot.park(addr_index, validate, timeout))
@@ -596,6 +602,10 @@ impl SharedMemory {
         timeout: Option<Instant>,
     ) -> Result<WaitResult, Trap> {
         let addr = validate_atomic_addr(&self.0.def.0, addr_index, 8, 8)?;
+        log::trace!(
+            "memory.atomic.wait64(addr={addr_index}, expected={expected}, timeout={timeout:?})"
+        );
+
         // SAFETY: `addr_index` was validated by `validate_atomic_addr` above.
         assert!(std::mem::size_of::<AtomicU64>() == 8);
         assert!(std::mem::align_of::<AtomicU64>() <= 8);