feat: add nicer `fmt::Debug` impls (#4)

* feat: add nicer `fmt::Debug` impls

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

src/mpsc/async_impl.rs

@@ -29,10 +29,12 @@ pub fn channel<T>(thingbuf: ThingBuf<T>) -> (Sender<T>, Receiver<T>) {
     (tx, rx)
 }
 
+#[derive(Debug)]
 pub struct Sender<T> {
     inner: Arc<Inner<T>>,
 }
 
+#[derive(Debug)]
 pub struct Receiver<T> {
     inner: Arc<Inner<T>>,
 }
@@ -62,6 +64,7 @@ pub struct RecvFuture<'a, T> {
     rx: &'a Receiver<T>,
 }
 
+#[derive(Debug)]
 struct Inner<T> {
     thingbuf: ThingBuf<T>,
     rx_wait: WaitCell<Waker>,

src/mpsc/sync.rs

@@ -30,10 +30,12 @@ pub fn channel<T>(thingbuf: ThingBuf<T>) -> (Sender<T>, Receiver<T>) {
     (tx, rx)
 }
 
+#[derive(Debug)]
 pub struct Sender<T> {
     inner: Arc<Inner<T>>,
 }
 
+#[derive(Debug)]
 pub struct Receiver<T> {
     inner: Arc<Inner<T>>,
 }
@@ -43,6 +45,7 @@ pub struct SendRef<'a, T> {
     slot: Ref<'a, T>,
 }
 
+#[derive(Debug)]
 struct Inner<T> {
     thingbuf: ThingBuf<T>,
     rx_wait: WaitCell<Thread>,

src/mpsc/tests/mpsc_async.rs

@@ -121,3 +121,17 @@ fn spsc_recv_then_send_then_close() {
         consumer.join().unwrap();
     })
 }
+
+#[test]
+fn tx_close_wakes() {
+    loom::model(|| {
+        let (tx, rx) = channel(ThingBuf::<i32>::new(2));
+        let consumer = thread::spawn(move || {
+            future::block_on(async move {
+                assert_eq!(rx.recv().await, None);
+            })
+        });
+        drop(tx);
+        consumer.join().unwrap();
+    });
+}

src/mpsc/tests/mpsc_sync.rs

@@ -109,3 +109,15 @@ fn spsc_recv_then_send_then_close() {
         consumer.join().unwrap();
     })
 }
+
+#[test]
+fn tx_close_wakes() {
+    loom::model(|| {
+        let (tx, rx) = sync::channel(ThingBuf::<i32>::new(2));
+        let consumer = thread::spawn(move || {
+            assert_eq!(rx.recv(), None);
+        });
+        drop(tx);
+        consumer.join().unwrap();
+    });
+}

src/static_thingbuf.rs

@@ -74,9 +74,10 @@ impl<T, const CAP: usize> Drop for StaticThingBuf<T, CAP> {
 
 impl<T, const CAP: usize> fmt::Debug for StaticThingBuf<T, CAP> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("ThingBuf")
-            .field("capacity", &self.capacity())
+        f.debug_struct("StaticThingBuf")
             .field("len", &self.len())
+            .field("slots", &format_args!("[...]"))
+            .field("core", &self.core)
             .finish()
     }
 }

src/thingbuf.rs

@@ -76,8 +76,9 @@ impl<T> Drop for ThingBuf<T> {
 impl<T> fmt::Debug for ThingBuf<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("ThingBuf")
-            .field("capacity", &self.capacity())
             .field("len", &self.len())
+            .field("slots", &format_args!("[...]"))
+            .field("core", &self.core)
             .finish()
     }
 }

src/util.rs

@@ -1,5 +1,8 @@
 use crate::loom;
-use core::ops::{Deref, DerefMut};
+use core::{
+    fmt,
+    ops::{Deref, DerefMut},
+};
 
 pub(crate) mod panic;
 pub(crate) mod wait;
@@ -12,7 +15,7 @@ pub(crate) struct Backoff(u8);
     not(any(target_arch = "x86_64", target_arch = "aarch64")),
     repr(align(64))
 )]
-#[derive(Clone, Copy, Default, Hash, PartialEq, Eq, Debug)]
+#[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
 pub(crate) struct CachePadded<T>(pub(crate) T);
 
 // === impl Backoff ===
@@ -68,3 +71,9 @@ impl<T> DerefMut for CachePadded<T> {
         &mut self.0
     }
 }
+
+impl<T: fmt::Debug> fmt::Debug for CachePadded<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}

src/util/wait.rs

@@ -1,11 +1,14 @@
 use crate::{
     loom::{
-        atomic::{AtomicUsize, Ordering::*},
+        atomic::{
+            AtomicUsize,
+            Ordering::{self, *},
+        },
         UnsafeCell,
     },
     util::panic::{self, RefUnwindSafe, UnwindSafe},
 };
-use core::{fmt, task::Waker};
+use core::{fmt, ops, task::Waker};
 
 #[cfg(feature = "std")]
 use crate::loom::thread;
@@ -43,52 +46,46 @@ pub(crate) trait Notify {
     fn notify(self);
 }
 
+#[derive(Eq, PartialEq, Copy, Clone)]
+struct State(usize);
+
 // === impl WaitCell ===
 
 impl<T: Notify + UnwindSafe + fmt::Debug> WaitCell<T> {
-    const WAITING: usize = 0b00;
-    const PARKING: usize = 0b01;
-    const NOTIFYING: usize = 0b10;
-    const TX_CLOSED: usize = 0b100;
-    const RX_CLOSED: usize = 0b1000;
-
     pub(crate) fn new() -> Self {
         Self {
-            lock: AtomicUsize::new(Self::WAITING),
+            lock: AtomicUsize::new(State::WAITING.0),
             waiter: UnsafeCell::new(None),
         }
     }
 
     pub(crate) fn close_rx(&self) {
-        self.lock.fetch_or(Self::RX_CLOSED, AcqRel);
+        test_dbg!(self.fetch_or(State::RX_CLOSED, AcqRel));
     }
 
     pub(crate) fn is_rx_closed(&self) -> bool {
-        test_dbg!(self.lock.load(Acquire) & Self::RX_CLOSED == Self::RX_CLOSED)
+        test_dbg!(self.current_state().contains(State::RX_CLOSED))
     }
 
     pub(crate) fn wait_with(&self, f: impl FnOnce() -> T) -> WaitResult {
         test_println!("registering waiter");
 
         // this is based on tokio's AtomicWaker synchronization strategy
-        match test_dbg!(self
-            .lock
-            .compare_exchange(Self::WAITING, Self::PARKING, AcqRel, Acquire,))
-        {
+        match test_dbg!(self.compare_exchange(State::WAITING, State::PARKING)) {
             // someone else is notifying the receiver, so don't park!
-            Err(actual) if test_dbg!(actual & Self::TX_CLOSED) == Self::TX_CLOSED => {
-                test_println!("-> state = TX_CLOSED");
+            Err(actual) if test_dbg!(actual.contains(State::TX_CLOSED)) => {
                 return WaitResult::TxClosed;
             }
-            Err(actual) if test_dbg!(actual & Self::NOTIFYING) == Self::NOTIFYING => {
-                test_println!("-> state = NOTIFYING");
+            Err(actual) if test_dbg!(actual.contains(State::NOTIFYING)) => {
                 // f().notify();
                 // loom::hint::spin_loop();
                 return WaitResult::Notified;
             }
 
             Err(actual) => {
-                debug_assert!(actual == Self::PARKING || actual == Self::PARKING | Self::NOTIFYING);
+                debug_assert!(
+                    actual == State::PARKING || actual == State::PARKING | State::NOTIFYING
+                );
                 return WaitResult::Wait;
             }
             Ok(_) => {}
@@ -106,29 +103,22 @@ impl<T: Notify + UnwindSafe + fmt::Debug> WaitCell<T> {
             Err(panic) => (Some(panic), None),
         };
 
-        let result = match test_dbg!(self.lock.compare_exchange(
-            Self::PARKING,
-            Self::WAITING,
-            AcqRel,
-            Acquire
-        )) {
+        let result = match test_dbg!(self.compare_exchange(State::PARKING, State::WAITING)) {
             Ok(_) => {
                 let _ = panic::catch_unwind(move || drop(prev_waiter));
 
                 WaitResult::Wait
             }
             Err(actual) => {
-                test_println!("-> was notified; state={:#b}", actual);
+                test_println!("-> was notified; state={:?}", actual);
                 let waiter = self.waiter.with_mut(|waiter| unsafe { (*waiter).take() });
                 // Reset to the WAITING state by clearing everything *except*
                 // the closed bits (which must remain set).
-                let state = test_dbg!(self
-                    .lock
-                    .fetch_and(Self::TX_CLOSED | Self::RX_CLOSED, AcqRel));
+                let state = test_dbg!(self.fetch_and(State::TX_CLOSED | State::RX_CLOSED, AcqRel));
                 // The only valid state transition while we were parking is to
                 // add the TX_CLOSED bit.
                 debug_assert!(
-                    state == actual || state == actual | Self::TX_CLOSED,
+                    state == actual || state == actual | State::TX_CLOSED,
                     "state changed unexpectedly while parking!"
                 );
 
@@ -143,7 +133,7 @@ impl<T: Notify + UnwindSafe + fmt::Debug> WaitCell<T> {
                     waiter.notify();
                 }
 
-                if state & Self::TX_CLOSED == Self::TX_CLOSED {
+                if test_dbg!(state.contains(State::TX_CLOSED)) {
                     WaitResult::TxClosed
                 } else {
                     WaitResult::Notified
@@ -169,15 +159,16 @@ impl<T: Notify + UnwindSafe + fmt::Debug> WaitCell<T> {
     fn notify2(&self, close: bool) {
         test_println!("notifying; close={:?};", close);
         let bits = if close {
-            Self::NOTIFYING | Self::TX_CLOSED
+            State::NOTIFYING | State::TX_CLOSED
         } else {
-            Self::NOTIFYING
+            State::NOTIFYING
         };
-        if test_dbg!(self.lock.fetch_or(bits, AcqRel)) == Self::WAITING {
+        test_dbg!(bits);
+        if test_dbg!(self.fetch_or(bits, AcqRel)) == State::WAITING {
             // we have the lock!
             let waiter = self.waiter.with_mut(|thread| unsafe { (*thread).take() });
 
-            self.lock.fetch_and(!Self::NOTIFYING, Release);
+            test_dbg!(self.fetch_and(!State::NOTIFYING, AcqRel));
 
             if let Some(waiter) = test_dbg!(waiter) {
                 waiter.notify();
@@ -186,6 +177,31 @@ impl<T: Notify + UnwindSafe + fmt::Debug> WaitCell<T> {
     }
 }
 
+impl<T> WaitCell<T> {
+    #[inline(always)]
+    fn compare_exchange(&self, State(curr): State, State(new): State) -> Result<State, State> {
+        self.lock
+            .compare_exchange(curr, new, AcqRel, Acquire)
+            .map(State)
+            .map_err(State)
+    }
+
+    #[inline(always)]
+    fn fetch_and(&self, State(state): State, order: Ordering) -> State {
+        State(self.lock.fetch_and(state, order))
+    }
+
+    #[inline(always)]
+    fn fetch_or(&self, State(state): State, order: Ordering) -> State {
+        State(self.lock.fetch_or(state, order))
+    }
+
+    #[inline(always)]
+    fn current_state(&self) -> State {
+        State(self.lock.load(Acquire))
+    }
+}
+
 #[cfg(feature = "std")]
 impl Notify for thread::Thread {
     fn notify(self) {
@@ -206,6 +222,78 @@ impl<T: RefUnwindSafe> RefUnwindSafe for WaitCell<T> {}
 unsafe impl<T: Send> Send for WaitCell<T> {}
 unsafe impl<T: Send> Sync for WaitCell<T> {}
 
+impl<T> fmt::Debug for WaitCell<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("WaitCell")
+            .field("state", &self.current_state())
+            .finish()
+    }
+}
+
+// === impl State ===
+
+impl State {
+    const WAITING: Self = Self(0b00);
+    const PARKING: Self = Self(0b01);
+    const NOTIFYING: Self = Self(0b10);
+    const TX_CLOSED: Self = Self(0b100);
+    const RX_CLOSED: Self = Self(0b1000);
+
+    fn contains(self, Self(state): Self) -> bool {
+        self.0 & state == state
+    }
+}
+
+impl ops::BitOr for State {
+    type Output = Self;
+
+    fn bitor(self, Self(rhs): Self) -> Self::Output {
+        Self(self.0 | rhs)
+    }
+}
+
+impl ops::Not for State {
+    type Output = Self;
+
+    fn not(self) -> Self::Output {
+        Self(!self.0)
+    }
+}
+
+impl fmt::Debug for State {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut has_states = false;
+        macro_rules! f_bits {
+            ($self: expr, $f: expr, $has_states: ident, $($name: ident),+) => {
+                $(
+                    if $self.contains(Self::$name) {
+                        if $has_states {
+                            $f.write_str(" | ")?;
+                        }
+                        $f.write_str(stringify!($name))?;
+                        $has_states = true;
+                    }
+                )+
+
+            };
+        }
+
+        f_bits!(self, f, has_states, PARKING, NOTIFYING, TX_CLOSED, RX_CLOSED);
+
+        if !has_states {
+            if *self == Self::WAITING {
+                return f.write_str("WAITING");
+            }
+
+            f.debug_tuple("UnknownState")
+                .field(&format_args!("{:#b}", self.0))
+                .finish()?;
+        }
+
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

tests/debug.rs

@@ -0,0 +1,12 @@
+use thingbuf::{mpsc, ThingBuf};
+
+#[test]
+fn mpsc_debug() {
+    let (tx, rx) = mpsc::channel(ThingBuf::new(4));
+    println!("tx={:#?}", tx);
+    println!("rx={:#?}", rx);
+    let _ = tx.try_send(1);
+    println!("rx={:#?}", rx);
+    drop(tx);
+    println!("rx={:#?}", rx);
+}