Sort before dedup and add comment for Epoll's thread_id

src/shims/unix/linux/epoll.rs

@@ -20,6 +20,7 @@ struct Epoll {
     // This is an Rc because EpollInterest need to hold a reference to update
     // it.
     ready_list: Rc<RefCell<BTreeMap<(FdId, i32), EpollEventInstance>>>,
+    /// A list of thread ids blocked on this epoll instance.
     thread_id: RefCell<Vec<ThreadId>>,
 }
 
@@ -596,6 +597,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 }
             }
         }
+        waiter.sort();
         waiter.dedup();
         for thread_id in waiter {
             this.unblock_thread(thread_id, BlockReason::Epoll)?;