Adding semantic next_event information to Task struct

Author: Dylan Wolff

shuttle/src/future/batch_semaphore.rs

@@ -1,7 +1,7 @@
 //! A counting semaphore supporting both async and sync operations.
 use crate::current;
 use crate::runtime::execution::ExecutionState;
-use crate::runtime::task::{clock::VectorClock, TaskId};
+use crate::runtime::task::{clock::VectorClock, Event, TaskId};
 use crate::runtime::thread;
 use crate::sync::{ResourceSignature, ResourceType};
 use std::cell::RefCell;
@@ -289,7 +289,6 @@ impl BatchSemaphoreState {
 pub struct BatchSemaphore {
     state: RefCell<BatchSemaphoreState>,
     fairness: Fairness,
-    #[allow(unused)]
     signature: ResourceSignature,
 }
 
@@ -392,8 +391,9 @@ impl BatchSemaphore {
 
     /// Closes the semaphore. This prevents the semaphore from issuing new
     /// permits and notifies all pending waiters.
+    #[track_caller]
     pub fn close(&self) {
-        thread::switch();
+        thread::switch(Event::batch_semaphore_rel(&self.signature));
 
         self.init_object_id();
         let mut state = self.state.borrow_mut();
@@ -436,8 +436,9 @@ impl BatchSemaphore {
     /// If the permits are available, returns Ok(())
     /// If the semaphore is closed, returns `Err(TryAcquireError::Closed)`
     /// If there aren't enough permits, returns `Err(TryAcquireError::NoPermits)`
+    #[track_caller]
     pub fn try_acquire(&self, num_permits: usize) -> Result<(), TryAcquireError> {
-        thread::switch();
+        thread::switch(Event::batch_semaphore_acq(&self.signature));
 
         self.init_object_id();
         let mut state = self.state.borrow_mut();
@@ -538,22 +539,25 @@ impl BatchSemaphore {
     }
 
     /// Acquire the specified number of permits (async API)
+    #[track_caller]
     pub fn acquire(&self, num_permits: usize) -> Acquire<'_> {
         // No switch here; switch should be triggered on polling future
         self.init_object_id();
         Acquire::new(self, num_permits)
     }
 
     /// Acquire the specified number of permits (blocking API)
+    #[track_caller]
     pub fn acquire_blocking(&self, num_permits: usize) -> Result<(), AcquireError> {
         // No switch here; switch should be triggered on polling future
         self.init_object_id();
         crate::future::block_on(self.acquire(num_permits))
     }
 
     /// Release `num_permits` back to the Semaphore
+    #[track_caller]
     pub fn release(&self, num_permits: usize) {
-        thread::switch();
+        thread::switch(Event::batch_semaphore_rel(&self.signature));
 
         self.init_object_id();
         if num_permits == 0 {
@@ -645,6 +649,7 @@ pub struct Acquire<'a> {
 }
 
 impl<'a> Acquire<'a> {
+    #[track_caller]
     fn new(semaphore: &'a BatchSemaphore, num_permits: usize) -> Self {
         let waiter = Arc::new(Waiter::new(num_permits));
         Self {
@@ -689,7 +694,7 @@ impl Future for Acquire<'_> {
         let blocking_is_not_commutative = self.semaphore.fairness == Fairness::StrictlyFair;
 
         if self.never_polled && (will_succeed || blocking_is_not_commutative) {
-            thread::switch();
+            thread::switch(Event::batch_semaphore_acq(&self.semaphore.signature));
         }
         self.never_polled = false;
 
@@ -778,12 +783,25 @@ impl Future for Acquire<'_> {
                             self.waiter.is_queued.store(true, Ordering::SeqCst);
                         }
                         trace!("Acquire::poll for waiter {:?} that is enqueued", self.waiter);
+
+                        let event = Event::batch_semaphore_acq(&self.semaphore.signature);
+                        ExecutionState::with(|s| unsafe { s.current_mut().set_next_event(event) });
+                        // SAFETY: This is safe because the current task immediately suspends after this future
+                        // returns Poll::Pending (src/future/mod.rs). Whenever a task resumes, the `next_event`
+                        // is unset, so there is no opportunity to corrupt the reference to our signature while
+                        // it is set as the `next_task`.
                         Poll::Pending
                     }
                     Err(TryAcquireError::Closed) => unreachable!(),
                 }
             } else {
                 // No progress made, future is still pending.
+                let event = Event::batch_semaphore_acq(&self.semaphore.signature);
+                // SAFETY: This is safe because the current task immediately suspends after this future
+                // returns Poll::Pending (src/future/mod.rs). Whenever a task resumes, the `next_event`
+                // is unset, so there is no opportunity to corrupt the reference to our signature while
+                // it is set as the `next_task`.
+                ExecutionState::with(|s| unsafe { s.current_mut().set_next_event(event) });
                 Poll::Pending
             }
         }

shuttle/src/future/mod.rs

@@ -251,7 +251,7 @@ pub fn block_on<F: Future>(future: F) -> F::Output {
             Poll::Ready(result) => break result,
             Poll::Pending => {
                 ExecutionState::with(|state| state.current_mut().sleep_unless_woken());
-                thread::switch();
+                thread::switch_keep_event();
             }
         }
     }

shuttle/src/runtime/execution.rs

@@ -2,7 +2,7 @@ use crate::runtime::failure::{init_panic_hook, persist_failure};
 use crate::runtime::storage::{StorageKey, StorageMap};
 use crate::runtime::task::clock::VectorClock;
 use crate::runtime::task::labels::Labels;
-use crate::runtime::task::{ChildLabelFn, Task, TaskId, TaskName, TaskSignature, DEFAULT_INLINE_TASKS};
+use crate::runtime::task::{ChildLabelFn, Event, Task, TaskId, TaskName, TaskSignature, DEFAULT_INLINE_TASKS};
 use crate::runtime::thread;
 use crate::runtime::thread::continuation::PooledContinuation;
 use crate::scheduler::{Schedule, Scheduler};
@@ -535,7 +535,8 @@ impl ExecutionState {
     where
         F: Future<Output = ()> + 'static,
     {
-        thread::switch();
+        let signature = ExecutionState::with(|state| state.current_mut().signature.new_child(caller));
+        thread::switch(Event::Spawn(&signature));
         let task_id = Self::with(|state| {
             let schedule_len = CurrentSchedule::len();
             let parent_span_id = state.top_level_span.id();
@@ -558,7 +559,7 @@ impl ExecutionState {
                 schedule_len,
                 tag,
                 Some(state.current().id()),
-                state.current_mut().signature.new_child(caller),
+                signature,
             );
 
             state.tasks.push(task);
@@ -578,7 +579,8 @@ impl ExecutionState {
         mut initial_clock: Option<VectorClock>,
         caller: &'static Location<'static>,
     ) -> TaskId {
-        thread::switch();
+        let signature = ExecutionState::with(|state| state.current_mut().signature.new_child(caller));
+        thread::switch(Event::Spawn(&signature));
         let task_id = Self::with(|state| {
             let parent_span_id = state.top_level_span.id();
             let task_id = TaskId(state.tasks.len());
@@ -605,7 +607,7 @@ impl ExecutionState {
                 CurrentSchedule::len(),
                 tag,
                 Some(state.current().id()),
-                state.current_mut().signature.new_child(caller),
+                signature,
             );
             state.tasks.push(task);
 
@@ -754,6 +756,10 @@ impl ExecutionState {
         self.tasks.get(id.0)
     }
 
+    pub(crate) fn try_current_mut(&mut self) -> Option<&mut Task> {
+        self.tasks.get_mut(self.current_task.id()?.0)
+    }
+
     pub(crate) fn in_cleanup(&self) -> bool {
         self.in_cleanup
     }
@@ -885,7 +891,7 @@ impl ExecutionState {
             .scheduler
             .borrow_mut()
             .next_task(task_refs, self.current_task.id(), is_yielding)
-            .map(ScheduledTask::Some)
+            .map(|task| ScheduledTask::Some(task.id()))
             .unwrap_or(ScheduledTask::Stopped);
 
         // Tracing this `in_scope` is purely a matter of taste. We do it because

shuttle/src/runtime/runner.rs

@@ -237,12 +237,12 @@ impl<S: Scheduler> Scheduler for PortfolioStoppableScheduler<S> {
         }
     }
 
-    fn next_task(
+    fn next_task<'a>(
         &mut self,
-        runnable_tasks: &[&Task],
+        runnable_tasks: &'a [&'a Task],
         current_task: Option<TaskId>,
         is_yielding: bool,
-    ) -> Option<TaskId> {
+    ) -> Option<&'a Task> {
         if self.stop_signal.load(Ordering::SeqCst) {
             None
         } else {

shuttle/src/runtime/task/mod.rs

@@ -251,6 +251,132 @@ impl PartialEq for TaskSignature {
 
 impl Eq for TaskSignature {}
 
+pub(crate) type Loc = &'static Location<'static>;
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub(crate) enum Event<'a> {
+    AtomicRead(&'a ResourceSignature, Loc),
+    AtomicWrite(&'a ResourceSignature, Loc),
+    AtomicReadWrite(&'a ResourceSignature, Loc),
+    BatchSemaphoreAcq(&'a ResourceSignature, Loc),
+    BatchSemaphoreRel(&'a ResourceSignature, Loc),
+    BarrierWait(&'a ResourceSignature, Loc),
+    CondvarWait(&'a ResourceSignature, Loc),
+    CondvarNotify(Loc),
+    Park(Loc),
+    Unpark(&'a TaskSignature, Loc),
+    ChannelSend(&'a ResourceSignature, Loc),
+    ChannelRecv(&'a ResourceSignature, Loc),
+    Spawn(&'a TaskSignature),
+    Yield(Loc),
+    Sleep(Loc),
+    Exit,
+    Join(&'a TaskSignature, Loc),
+    Unknown,
+}
+
+impl<'a> std::fmt::Display for Event<'a> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Event::AtomicRead(_, loc) => write!(f, "AtomicRead at {}", loc),
+            Event::AtomicWrite(_, loc) => write!(f, "AtomicWrite at {}", loc),
+            Event::AtomicReadWrite(_, loc) => write!(f, "AtomicReadWrite at {}", loc),
+            Event::BatchSemaphoreAcq(_, loc) => write!(f, "BatchSemaphoreAcq at {}", loc),
+            Event::BatchSemaphoreRel(_, loc) => write!(f, "BatchSemaphoreRel at {}", loc),
+            Event::BarrierWait(_, loc) => write!(f, "BarrierWait at {}", loc),
+            Event::CondvarWait(_, loc) => write!(f, "CondvarWait at {}", loc),
+            Event::CondvarNotify(loc) => write!(f, "CondvarNotify at {}", loc),
+            Event::Park(loc) => write!(f, "Park at {}", loc),
+            Event::Unpark(_, loc) => write!(f, "Unpark at {}", loc),
+            Event::ChannelSend(_, loc) => write!(f, "ChannelSend at {}", loc),
+            Event::ChannelRecv(_, loc) => write!(f, "ChannelRecv at {}", loc),
+            Event::Spawn(sig) => write!(f, "Spawn at {}", sig.task_creation_stack.last().unwrap().0),
+            Event::Yield(loc) => write!(f, "Yield at {}", loc),
+            Event::Sleep(loc) => write!(f, "Sleep at {}", loc),
+            Event::Exit => write!(f, "Exit"),
+            Event::Join(_, loc) => write!(f, "Join at {}", loc),
+            Event::Unknown => write!(f, "Unknown"),
+        }
+    }
+}
+
+impl<'a> Event<'a> {
+    #[track_caller]
+    pub(crate) fn atomic_read(sig: &'a ResourceSignature) -> Self {
+        Self::AtomicRead(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn atomic_write(sig: &'a ResourceSignature) -> Self {
+        Self::AtomicWrite(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn atomic_read_write(sig: &'a ResourceSignature) -> Self {
+        Self::AtomicReadWrite(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn batch_semaphore_acq(sig: &'a ResourceSignature) -> Self {
+        Self::BatchSemaphoreAcq(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn batch_semaphore_rel(sig: &'a ResourceSignature) -> Self {
+        Self::BatchSemaphoreRel(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn barrier_wait(sig: &'a ResourceSignature) -> Self {
+        Self::BarrierWait(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn condvar_wait(sig: &'a ResourceSignature) -> Self {
+        Self::CondvarWait(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn condvar_notify() -> Self {
+        Self::CondvarNotify(Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn park() -> Self {
+        Self::Park(Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn unpark(sig: &'a TaskSignature) -> Self {
+        Self::Unpark(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn channel_send(sig: &'a ResourceSignature) -> Self {
+        Self::ChannelSend(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn channel_recv(sig: &'a ResourceSignature) -> Self {
+        Self::ChannelRecv(sig, Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn yield_now() -> Self {
+        Self::Yield(Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn sleep() -> Self {
+        Self::Sleep(Location::caller())
+    }
+
+    #[track_caller]
+    pub(crate) fn join(sig: &'a TaskSignature) -> Self {
+        Self::Join(sig, Location::caller())
+    }
+}
+
 /// A `Task` represents a user-level unit of concurrency. Each task has an `id` that is unique within
 /// the execution, and a `state` reflecting whether the task is runnable (enabled) or not.
 #[derive(Debug)]
@@ -271,6 +397,8 @@ pub struct Task {
     // Remember whether the waker was invoked while we were running
     woken: bool,
 
+    next_event: Event<'static>,
+
     name: Option<String>,
 
     local_storage: StorageMap,
@@ -342,6 +470,7 @@ impl Task {
             waiter: None,
             waker,
             woken: false,
+            next_event: Event::Unknown,
             detached: false,
             park_state: ParkState::default(),
             name,
@@ -416,7 +545,7 @@ impl Task {
                 let cx = &mut Context::from_waker(&waker);
                 while future.as_mut().poll(cx).is_pending() {
                     ExecutionState::with(|state| state.current_mut().sleep_unless_woken());
-                    thread::switch();
+                    thread::switch_keep_event();
                 }
             }),
             stack_size,
@@ -664,6 +793,19 @@ impl Task {
             }
         )
     }
+
+    /// Get the next_event with a downcast lifetime tied to self.
+    pub(crate) fn next_event(&self) -> &Event<'_> {
+        unsafe { std::mem::transmute(&self.next_event) }
+    }
+
+    pub(crate) unsafe fn set_next_event(&mut self, event: Event<'_>) {
+        self.next_event = unsafe { std::mem::transmute::<Event<'_>, Event<'static>>(event) };
+    }
+
+    pub(crate) fn unset_next_event(&mut self) {
+        self.next_event = Event::Unknown;
+    }
 }
 
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]