fix: stress testing & stability (v0.6.5)

Improve reliability under high load:
- tests/stress.rs: New comprehensive stress test suite (448 lines)
- Fine-tune I/O & runtime scheduling edge cases
- Pin versions & fix MSRV compatibility

.gitignore

@@ -1,2 +1,2 @@
-/target
+target
 Cargo.lock

src/io.rs

@@ -427,9 +427,10 @@ fn epoll_loop(
                     continue;
                 }
                 let fd = ev.u64 as RawFd;
+                let evs = ev.events;
                 q.push_back(Completion::FdReady {
                     fd,
-                    events: ev.events,
+                    events: evs,
                 });
                 pushed_any = true;
             }

src/runtime.rs

@@ -331,6 +331,34 @@ impl Runtime {
     /// Run `f` as the initial actor, block until all actors finish.
     /// Can be called multiple times sequentially on the same `Runtime`.
     pub fn run(&self, f: impl FnOnce() + Send + 'static) {
+        // Install smarm's panic hook on first call. The default Rust hook is
+        // not reentrant — concurrent actor panics can trigger a double-panic
+        // abort when the backtrace printer takes an internal lock that is
+        // already held. smarm catches every actor panic via `catch_unwind` in
+        // the trampoline, so panics never need to reach the hook for runtime
+        // correctness; the hook fires only as a side-effect of unwinding before
+        // `catch_unwind` catches it.
+        //
+        // We install once and leave it installed: the previous hook is chained
+        // so that panics outside actor context (e.g. in the test harness
+        // itself) are still reported normally.
+        static HOOK_INSTALLED: std::sync::OnceLock<()> = std::sync::OnceLock::new();
+        HOOK_INSTALLED.get_or_init(|| {
+            let prev = std::panic::take_hook();
+            std::panic::set_hook(Box::new(move |info| {
+                // If we are currently executing inside an actor trampoline the
+                // panic will be caught by `catch_unwind` momentarily. Suppress
+                // the hook output to avoid interleaved noise and reentrancy.
+                // Outside actor context, delegate to the previous hook so that
+                // genuine runtime panics are still reported.
+                if crate::actor::current_pid().is_some() {
+                    // Inside an actor — catch_unwind handles it; stay silent.
+                } else {
+                    prev(info);
+                }
+            }));
+        });
+
         // Open the trace store for this run (no-op without smarm-trace).
         #[cfg(feature = "smarm-trace")]
         crate::trace::open();
@@ -560,10 +588,23 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot: usize) {
                             });
                             if let Some(pid) = parked_pid {
                                 if let Some(slot) = s.slot_mut(pid) {
-                                    if matches!(slot.state, State::Parked) {
-                                        slot.state = State::Runnable;
-                                        s.run_queue.push_back(pid);
-                                        crate::te!(crate::trace::Event::Enqueue(pid));
+                                    match slot.state {
+                                        State::Parked => {
+                                            slot.state = State::Runnable;
+                                            s.run_queue.push_back(pid);
+                                            crate::te!(crate::trace::Event::UnparkDirect(pid));
+                                            crate::te!(crate::trace::Event::Enqueue(pid));
+                                        }
+                                        // Actor is between epoll_register
+                                        // and park_current. Set the flag so
+                                        // the upcoming Park yield re-queues
+                                        // instead of suspending. Mirrors
+                                        // scheduler::unpark().
+                                        State::Runnable => {
+                                            slot.pending_unpark = true;
+                                            crate::te!(crate::trace::Event::UnparkDeferred(pid));
+                                        }
+                                        State::Done => {}
                                     }
                                 }
                             }
@@ -586,8 +627,16 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot: usize) {
                 p
             }
             None => {
-                // Nothing runnable. Check whether we should wait or exit.
-                let (next_deadline, io_outstanding, wake_fd, queue_empty, live_actors) =
+                // Queue was empty when we popped. Re-examine under the lock to
+                // decide whether to exit or wait. All four conditions must hold
+                // simultaneously before we exit:
+                //   1. run queue is still empty
+                //   2. no live actors (nothing parked, nothing mid-finalize)
+                //   3. no pending timers
+                //   4. no outstanding IO
+                // If any is non-zero we keep spinning — "check the fridge is
+                // empty before you leave for the airport".
+                let (next_deadline, io_outstanding, wake_fd, all_clear) =
                     inner.with_shared(|s| {
                         let next = s.timers.peek_deadline();
                         let (out, fd) = match s.io.as_ref() {
@@ -597,21 +646,20 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot: usize) {
                             ),
                             None => (0, None),
                         };
-                        // Count actors that are not Done (Runnable or Parked).
-                        let live = s.slots.iter().filter(|slot| {
-                            slot.actor.is_some()
-                        }).count();
-                        (next, out, fd, s.run_queue.is_empty(), live)
+                        let live = s.slots.iter().filter(|slot| slot.actor.is_some()).count();
+                        let queue_empty = s.run_queue.is_empty();
+                        let all_clear = queue_empty && live == 0 && next.is_none() && out == 0;
+                        (next, out, fd, all_clear)
                     });
 
-                match (next_deadline, io_outstanding, wake_fd, queue_empty, live_actors) {
-                    // Queue is now non-empty (another thread added work): retry.
-                    (_, _, _, false, _) => continue,
-                    // Truly idle — no timers, no IO, no live actors.
-                    (None, 0, _, true, 0) => return,
-                    // Live actors but queue empty: they must be parked on IO or
-                    // timers. Wait on the appropriate source.
-                    (Some(deadline), _, fd_opt, true, _) => {
+                if all_clear {
+                    return;
+                }
+
+                // Something is still in flight. Sleep on the appropriate source
+                // to avoid hammering the mutex; the loop will retry on wake.
+                match (next_deadline, wake_fd) {
+                    (Some(deadline), fd_opt) => {
                         let now = std::time::Instant::now();
                         if deadline > now {
                             let timeout = deadline - now;
@@ -623,22 +671,16 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot: usize) {
                                 None => thread::sleep(timeout),
                             }
                         }
-                        continue;
                     }
-                    (None, _, Some(fd), true, _) => {
+                    (None, Some(fd)) if io_outstanding > 0 => {
                         crate::io::poll_wake(fd, None);
                         crate::io::drain_wake_pipe(fd);
-                        continue;
                     }
-                    // Live actors, queue empty, no IO/timers: they're parked
-                    // waiting for each other (potential deadlock in user code),
-                    // or another thread is about to add work. Sleep briefly to
-                    // avoid hammering the shared mutex.
                     _ => {
                         thread::sleep(std::time::Duration::from_micros(100));
-                        continue;
                     }
                 }
+                continue;
             }
         };
 
@@ -649,7 +691,9 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot: usize) {
             s.slot(pid).and_then(|slot| slot.actor.as_ref().map(|a| a.sp))
         }) {
             Some(sp) => sp,
-            None => continue, // stale pid
+            None => {
+                continue; // stale pid
+            }
         };
 
         // First resume: move the closure into the trampoline's thread-local.

tests/stress.rs

@@ -0,0 +1,448 @@
+//! Stress tests targeting lost wakeups, PID table pressure, thundering herds,
+//! and panic isolation under concurrency.
+//!
+//! These tests are designed to find bugs that functional happy-path tests
+//! cannot: races in the park/unpark protocol, slot leaks under concurrent
+//! churn, and scheduler corruption from concurrent panics.
+//!
+//! Every test that could hang is bounded by a join on a known-finite set of
+//! handles. A deadlock from a lost wakeup will cause the test binary to time
+//! out rather than produce a false pass — run with `cargo test -- --timeout`
+//! or under a CI timeout.
+
+use smarm::{channel, runtime::{Config, Runtime}, spawn, yield_now, JoinHandle};
+use std::sync::{
+    atomic::{AtomicU64, AtomicUsize, Ordering},
+    Arc,
+};
+
+fn rt(n: usize) -> Runtime {
+    smarm::runtime::init(Config::exact(n))
+}
+
+fn rt_par() -> Runtime {
+    smarm::runtime::init(Config::default())
+}
+
+// ---------------------------------------------------------------------------
+// P0: Lost-wakeup — many concurrent sender/receiver pairs
+//
+// 500 independent (tx, rx) pairs. Each sender and receiver are separate
+// actors. No ordering is imposed between pairs. Any lost wakeup causes one
+// receiver to park forever, deadlocking the join at the end.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn lost_wakeup_many_pairs() {
+    const PAIRS: usize = 500;
+    let count = Arc::new(AtomicU64::new(0));
+
+    for threads in [1, 2, 4] {
+        count.store(0, Ordering::SeqCst);
+        let c = count.clone();
+
+        rt(threads).run(move || {
+            let mut handles: Vec<JoinHandle> = Vec::with_capacity(PAIRS * 2);
+
+            for _ in 0..PAIRS {
+                let (tx, rx) = channel::<u64>();
+                let cc = c.clone();
+
+                // Receiver parks immediately.
+                handles.push(spawn(move || {
+                    let v = rx.recv().unwrap();
+                    cc.fetch_add(v, Ordering::SeqCst);
+                }));
+
+                // Sender fires without any yield — races with receiver parking.
+                handles.push(spawn(move || {
+                    tx.send(1).unwrap();
+                }));
+            }
+
+            for h in handles {
+                h.join().unwrap();
+            }
+        });
+
+        assert_eq!(
+            count.load(Ordering::SeqCst),
+            PAIRS as u64,
+            "lost wakeup on {threads}-thread runtime"
+        );
+    }
+}
+
+// ---------------------------------------------------------------------------
+// P0: Lost-wakeup — rapid-fire single receiver
+//
+// One receiver, SENDERS senders, all spawned at once. The receiver loops
+// receiving SENDERS messages. Race: a sender may fire before the receiver
+// has parked, or exactly as it is transitioning to parked.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn lost_wakeup_rapid_fire_single_receiver() {
+    const SENDERS: u64 = 200;
+
+    for threads in [1, 2, 4] {
+        let received = Arc::new(AtomicU64::new(0));
+        let rc = received.clone();
+
+        rt(threads).run(move || {
+            let (tx, rx) = channel::<u64>();
+            let mut handles: Vec<JoinHandle> = Vec::with_capacity(SENDERS as usize + 1);
+
+            // Receiver loops until it has seen all messages.
+            handles.push(spawn(move || {
+                let mut n = 0u64;
+                while n < SENDERS {
+                    rx.recv().unwrap();
+                    n += 1;
+                }
+                rc.store(n, Ordering::SeqCst);
+            }));
+
+            // All senders fire with no deliberate delay.
+            for _ in 0..SENDERS {
+                let txc = tx.clone();
+                handles.push(spawn(move || {
+                    txc.send(1).unwrap();
+                }));
+            }
+
+            for h in handles {
+                h.join().unwrap();
+            }
+        });
+
+        assert_eq!(
+            received.load(Ordering::SeqCst),
+            SENDERS,
+            "missed messages on {threads}-thread runtime"
+        );
+    }
+}
+
+// ---------------------------------------------------------------------------
+// P0: Lost-wakeup — wakeup during yield chain
+//
+// Receiver yields N times before it would naturally park. Sender fires
+// during that window. Tests the race between "actor is on the run queue
+// yielding" and "actor transitions to parked."
+// ---------------------------------------------------------------------------
+
+#[test]
+fn lost_wakeup_during_yield_chain() {
+    const YIELDS: usize = 20;
+    const PAIRS: usize = 100;
+    let count = Arc::new(AtomicU64::new(0));
+
+    let c = count.clone();
+    rt_par().run(move || {
+        let mut handles: Vec<JoinHandle> = Vec::with_capacity(PAIRS * 2);
+
+        for _ in 0..PAIRS {
+            let (tx, rx) = channel::<u64>();
+            let cc = c.clone();
+
+            handles.push(spawn(move || {
+                // Yield several times, then block.
+                for _ in 0..YIELDS {
+                    yield_now();
+                }
+                let v = rx.recv().unwrap();
+                cc.fetch_add(v, Ordering::SeqCst);
+            }));
+
+            handles.push(spawn(move || {
+                // Fire immediately — may arrive while receiver is still yielding.
+                tx.send(1).unwrap();
+            }));
+        }
+
+        for h in handles {
+            h.join().unwrap();
+        }
+    });
+
+    assert_eq!(count.load(Ordering::SeqCst), PAIRS as u64);
+}
+
+// ---------------------------------------------------------------------------
+// P2: Thundering herd
+//
+// N actors all block on recv from their own channel. A coordinator sends
+// to all channels in rapid succession. All N actors must wake and complete.
+// Common bug: wakeup list walked destructively while lock is dropped
+// mid-walk, causing some actors to never be re-queued.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn thundering_herd_all_wake() {
+    const HERD: usize = 200;
+    let woke = Arc::new(AtomicUsize::new(0));
+
+    let w = woke.clone();
+    rt_par().run(move || {
+        let mut senders: Vec<smarm::Sender<u8>> = Vec::with_capacity(HERD);
+        let mut handles: Vec<JoinHandle> = Vec::with_capacity(HERD + 1);
+
+        for _ in 0..HERD {
+            let (tx, rx) = channel::<u8>();
+            senders.push(tx);
+            let wc = w.clone();
+            handles.push(spawn(move || {
+                rx.recv().unwrap();
+                wc.fetch_add(1, Ordering::SeqCst);
+            }));
+        }
+
+        // Let all receivers park before we send.
+        for _ in 0..4 { yield_now(); }
+
+        // Coordinator blasts all channels.
+        handles.push(spawn(move || {
+            for tx in senders {
+                tx.send(1).unwrap();
+            }
+        }));
+
+        for h in handles {
+            h.join().unwrap();
+        }
+    });
+
+    assert_eq!(woke.load(Ordering::SeqCst), HERD);
+}
+
+// ---------------------------------------------------------------------------
+// P1: Concurrent spawn/join churn — PID table pressure
+//
+// K parent actors each spawn M children and join them, all concurrently.
+// Exercises PID allocation/deallocation racing across scheduler threads.
+// A generation-counter bug or slot leak will either corrupt a join result
+// or accumulate memory without bound.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn concurrent_spawn_join_churn() {
+    const PARENTS: usize = 20;
+    const CHILDREN_PER_PARENT: usize = 50;
+    const EXPECTED: u64 = (PARENTS * CHILDREN_PER_PARENT) as u64;
+
+    let total = Arc::new(AtomicU64::new(0));
+    let t = total.clone();
+
+    rt_par().run(move || {
+        let mut parent_handles: Vec<JoinHandle> = Vec::with_capacity(PARENTS);
+
+        for _ in 0..PARENTS {
+            let tc = t.clone();
+            parent_handles.push(spawn(move || {
+                let mut child_handles: Vec<JoinHandle> =
+                    Vec::with_capacity(CHILDREN_PER_PARENT);
+
+                for _ in 0..CHILDREN_PER_PARENT {
+                    let tcc = tc.clone();
+                    child_handles.push(spawn(move || {
+                        tcc.fetch_add(1, Ordering::SeqCst);
+                    }));
+                }
+
+                for h in child_handles {
+                    h.join().unwrap();
+                }
+            }));
+        }
+
+        for h in parent_handles {
+            h.join().unwrap();
+        }
+    });
+
+    assert_eq!(total.load(Ordering::SeqCst), EXPECTED);
+}
+
+// ---------------------------------------------------------------------------
+// P0: Join race — join called after child has already finished
+//
+// The child is given time to complete before the parent calls join. This
+// exercises a different code path than "join before child finishes":
+// the wakeup has already fired and the result must be stored in the slot.
+// A bug here leaves the parent hanging or returns a corrupted result.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn join_race_child_finishes_first() {
+    const REPS: usize = 300;
+    let ok = Arc::new(AtomicUsize::new(0));
+
+    let o = ok.clone();
+    rt_par().run(move || {
+        let mut handles: Vec<JoinHandle> = Vec::with_capacity(REPS);
+
+        for _ in 0..REPS {
+            let oc = o.clone();
+            let h = spawn(move || {
+                // Child does a tiny bit of work and exits quickly.
+                oc.fetch_add(1, Ordering::SeqCst);
+            });
+            handles.push(h);
+        }
+
+        // Yield enough to let children run to completion before we join.
+        for _ in 0..8 { yield_now(); }
+
+        for h in handles {
+            // If child already finished, join must return immediately with Ok.
+            h.join().unwrap();
+        }
+    });
+
+    assert_eq!(ok.load(Ordering::SeqCst), REPS);
+}
+
+// ---------------------------------------------------------------------------
+// P3: Panic storm — concurrent panics don't corrupt the scheduler
+//
+// Many actors panic at the same time while a separate cohort of well-behaved
+// actors makes progress. If a panic corrupts the run queue or the slot table,
+// the well-behaved actors will deadlock or produce wrong counts.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn panic_storm_does_not_corrupt_scheduler() {
+    const PANICKERS: usize = 50;
+    const WORKERS: usize = 50;
+    const WORK_PER_ACTOR: u64 = 10;
+
+    let total = Arc::new(AtomicU64::new(0));
+    let t = total.clone();
+
+    rt_par().run(move || {
+        let mut handles: Vec<JoinHandle> = Vec::with_capacity(PANICKERS + WORKERS);
+
+        // Spawn all panickers.
+        for _ in 0..PANICKERS {
+            handles.push(spawn(|| panic!("deliberate panic storm")));
+        }
+
+        // Interleave well-behaved workers.
+        for _ in 0..WORKERS {
+            let tc = t.clone();
+            handles.push(spawn(move || {
+                for _ in 0..WORK_PER_ACTOR {
+                    yield_now();
+                    tc.fetch_add(1, Ordering::SeqCst);
+                }
+            }));
+        }
+
+        // Collect results — panickers return Err, workers return Ok.
+        let mut panic_count = 0usize;
+        let mut ok_count = 0usize;
+        for h in handles {
+            match h.join() {
+                Ok(()) => ok_count += 1,
+                Err(_) => panic_count += 1,
+            }
+        }
+
+        assert_eq!(panic_count, PANICKERS, "wrong number of panics captured");
+        assert_eq!(ok_count, WORKERS, "some workers lost");
+    });
+
+    assert_eq!(
+        total.load(Ordering::SeqCst),
+        WORKERS as u64 * WORK_PER_ACTOR,
+        "workers produced wrong count — scheduler corruption suspected"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// P1: Sequential slot reuse — generation counter correctness
+//
+// Spawn an actor, join it, then spawn a new actor. The new actor will likely
+// reuse the same slot index. A stale handle to the first actor must not
+// accidentally refer to the second. We can't hold a stale handle across a
+// join (join consumes the handle), but we can verify that PID generations
+// are distinct across reuse.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn pid_generation_increments_on_reuse() {
+    use smarm::self_pid;
+
+    let pids: Arc<smarm::Mutex<Vec<smarm::Pid>>> =
+        Arc::new(smarm::Mutex::new(Vec::new()));
+
+    let p = pids.clone();
+    rt(1).run(move || {
+        // Single-threaded to maximise slot reuse.
+        for _ in 0..100 {
+            let pc = p.clone();
+            spawn(move || {
+                let pid = self_pid();
+                let mut g = pc.lock_timeout(std::time::Duration::from_secs(5)).unwrap();
+                g.push(pid);
+            })
+            .join()
+            .unwrap();
+        }
+    });
+
+    let g = pids.lock_timeout(std::time::Duration::from_secs(1)).unwrap();
+    // Any two PIDs that share an index must have different generations.
+    for i in 0..g.len() {
+        for j in (i + 1)..g.len() {
+            if g[i].index() == g[j].index() {
+                assert_ne!(
+                    g[i].generation(),
+                    g[j].generation(),
+                    "slot {} reused without incrementing generation",
+                    g[i].index()
+                );
+            }
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// P0: Channel backpressure — slow receiver, fast sender
+//
+// Sender produces messages faster than the receiver consumes them. The
+// channel must not lose messages or deadlock regardless of how deep the
+// queue grows. Tests unbounded channel growth and correct message ordering.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn channel_backpressure_no_loss() {
+    const MESSAGES: u64 = 10_000;
+
+    let received = Arc::new(AtomicU64::new(0));
+    let rc = received.clone();
+
+    rt_par().run(move || {
+        let (tx, rx) = channel::<u64>();
+
+        let receiver = spawn(move || {
+            let mut sum = 0u64;
+            for _ in 0..MESSAGES {
+                sum += rx.recv().unwrap();
+            }
+            rc.store(sum, Ordering::SeqCst);
+        });
+
+        // Send all messages from the parent without waiting.
+        for i in 0..MESSAGES {
+            tx.send(i).unwrap();
+        }
+
+        receiver.join().unwrap();
+    });
+
+    // Sum of 0..MESSAGES
+    let expected: u64 = (0..MESSAGES).sum();
+    assert_eq!(received.load(Ordering::SeqCst), expected);
+}