std: fix busy-waiting in Once::wait_force, add more tests

Author: joboet

library/std/src/sync/once/tests.rs

@@ -1,7 +1,9 @@
 use super::Once;
 use crate::panic;
+use crate::sync::atomic::{AtomicBool, Ordering::Relaxed};
 use crate::sync::mpsc::channel;
 use crate::thread;
+use crate::time::Duration;
 
 #[test]
 fn smoke_once() {
@@ -114,3 +116,47 @@ fn wait_for_force_to_finish() {
     assert!(t1.join().is_ok());
     assert!(t2.join().is_ok());
 }
+
+#[test]
+fn wait() {
+    for _ in 0..50 {
+        let val = AtomicBool::new(false);
+        let once = Once::new();
+
+        thread::scope(|s| {
+            for _ in 0..4 {
+                s.spawn(|| {
+                    once.wait();
+                    assert!(val.load(Relaxed));
+                });
+            }
+
+            once.call_once(|| val.store(true, Relaxed));
+        });
+    }
+}
+
+#[test]
+fn wait_on_poisoned() {
+    let once = Once::new();
+
+    panic::catch_unwind(|| once.call_once(|| panic!())).unwrap_err();
+    panic::catch_unwind(|| once.wait()).unwrap_err();
+}
+
+#[test]
+fn wait_force_on_poisoned() {
+    let once = Once::new();
+
+    thread::scope(|s| {
+        panic::catch_unwind(|| once.call_once(|| panic!())).unwrap_err();
+
+        s.spawn(|| {
+            thread::sleep(Duration::from_millis(100));
+
+            once.call_once_force(|_| {});
+        });
+
+        once.wait_force();
+    })
+}

library/std/src/sys/sync/once/queue.rs

@@ -157,7 +157,7 @@ impl Once {
                     panic!("Once instance has previously been poisoned");
                 }
                 _ => {
-                    current = wait(&self.state_and_queue, current);
+                    current = wait(&self.state_and_queue, current, !ignore_poisoning);
                 }
             }
         }
@@ -220,14 +220,18 @@ impl Once {
                     // All other values must be RUNNING with possibly a
                     // pointer to the waiter queue in the more significant bits.
                     assert!(state == RUNNING);
-                    current = wait(&self.state_and_queue, current);
+                    current = wait(&self.state_and_queue, current, true);
                 }
             }
         }
     }
 }
 
-fn wait(state_and_queue: &AtomicPtr<()>, mut current: StateAndQueue) -> StateAndQueue {
+fn wait(
+    state_and_queue: &AtomicPtr<()>,
+    mut current: StateAndQueue,
+    return_on_poisoned: bool,
+) -> StateAndQueue {
     let node = &Waiter {
         thread: Cell::new(Some(thread::current())),
         signaled: AtomicBool::new(false),
@@ -239,7 +243,7 @@ fn wait(state_and_queue: &AtomicPtr<()>, mut current: StateAndQueue) -> StateAnd
         let queue = to_queue(current);
 
         // If initialization has finished, return.
-        if matches!(state, POISONED | COMPLETE) {
+        if state == COMPLETE || (return_on_poisoned && state == POISONED) {
             return current;
         }