Don't explicitly panic or block when avoidable

src/lib.rs

@@ -46,7 +46,7 @@ use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::pin::Pin;
 use std::rc::Rc;
 use std::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
-use std::sync::{Arc, Mutex, MutexGuard, RwLock, TryLockError};
+use std::sync::{Arc, Mutex, MutexGuard, PoisonError, RwLock, TryLockError};
 use std::task::{Context, Poll, Waker};
 
 use async_task::{Builder, Runnable};
@@ -350,7 +350,8 @@ impl<'a> Executor<'a> {
 
         // TODO: If possible, push into the current local queue and notify the ticker.
         move |runnable| {
-            state.queue.push(runnable).unwrap();
+            let result = state.queue.push(runnable);
+            debug_assert!(result.is_ok()); // Since we use unbounded queue, push will never fail.
             state.notify();
         }
     }
@@ -696,7 +697,7 @@ impl State {
 
     /// Returns a reference to currently active tasks.
     fn active(&self) -> MutexGuard<'_, Slab<Waker>> {
-        self.active.lock().unwrap_or_else(|e| e.into_inner())
+        self.active.lock().unwrap_or_else(PoisonError::into_inner)
     }
 
     /// Notifies a sleeping ticker.
@@ -707,7 +708,11 @@ impl State {
             .compare_exchange(false, true, Ordering::AcqRel, Ordering::Acquire)
             .is_ok()
         {
-            let waker = self.sleepers.lock().unwrap().notify();
+            let waker = self
+                .sleepers
+                .lock()
+                .unwrap_or_else(PoisonError::into_inner)
+                .notify();
             if let Some(w) = waker {
                 w.wake();
             }
@@ -852,7 +857,11 @@ impl Ticker<'_> {
     ///
     /// Returns `false` if the ticker was already sleeping and unnotified.
     fn sleep(&mut self, waker: &Waker) -> bool {
-        let mut sleepers = self.state.sleepers.lock().unwrap();
+        let mut sleepers = self
+            .state
+            .sleepers
+            .lock()
+            .unwrap_or_else(PoisonError::into_inner);
 
         match self.sleeping {
             // Move to sleeping state.
@@ -878,7 +887,11 @@ impl Ticker<'_> {
     /// Moves the ticker into woken state.
     fn wake(&mut self) {
         if self.sleeping != 0 {
-            let mut sleepers = self.state.sleepers.lock().unwrap();
+            let mut sleepers = self
+                .state
+                .sleepers
+                .lock()
+                .unwrap_or_else(PoisonError::into_inner);
             sleepers.remove(self.sleeping);
 
             self.state
@@ -926,7 +939,11 @@ impl Drop for Ticker<'_> {
     fn drop(&mut self) {
         // If this ticker is in sleeping state, it must be removed from the sleepers list.
         if self.sleeping != 0 {
-            let mut sleepers = self.state.sleepers.lock().unwrap();
+            let mut sleepers = self
+                .state
+                .sleepers
+                .lock()
+                .unwrap_or_else(PoisonError::into_inner);
             let notified = sleepers.remove(self.sleeping);
 
             self.state
@@ -971,7 +988,7 @@ impl Runner<'_> {
         state
             .local_queues
             .write()
-            .unwrap()
+            .unwrap_or_else(PoisonError::into_inner)
             .push(runner.local.clone());
         runner
     }
@@ -993,25 +1010,25 @@ impl Runner<'_> {
                 }
 
                 // Try stealing from other runners.
-                let local_queues = self.state.local_queues.read().unwrap();
-
-                // Pick a random starting point in the iterator list and rotate the list.
-                let n = local_queues.len();
-                let start = rng.usize(..n);
-                let iter = local_queues
-                    .iter()
-                    .chain(local_queues.iter())
-                    .skip(start)
-                    .take(n);
-
-                // Remove this runner's local queue.
-                let iter = iter.filter(|local| !Arc::ptr_eq(local, &self.local));
-
-                // Try stealing from each local queue in the list.
-                for local in iter {
-                    steal(local, &self.local);
-                    if let Ok(r) = self.local.pop() {
-                        return Some(r);
+                if let Ok(local_queues) = self.state.local_queues.try_read() {
+                    // Pick a random starting point in the iterator list and rotate the list.
+                    let n = local_queues.len();
+                    let start = rng.usize(..n);
+                    let iter = local_queues
+                        .iter()
+                        .chain(local_queues.iter())
+                        .skip(start)
+                        .take(n);
+
+                    // Remove this runner's local queue.
+                    let iter = iter.filter(|local| !Arc::ptr_eq(local, &self.local));
+
+                    // Try stealing from each local queue in the list.
+                    for local in iter {
+                        steal(local, &self.local);
+                        if let Ok(r) = self.local.pop() {
+                            return Some(r);
+                        }
                     }
                 }
 
@@ -1037,7 +1054,7 @@ impl Drop for Runner<'_> {
         self.state
             .local_queues
             .write()
-            .unwrap()
+            .unwrap_or_else(PoisonError::into_inner)
             .retain(|local| !Arc::ptr_eq(local, &self.local));
 
         // Re-schedule remaining tasks in the local queue.