Merge #191

191: Add initial parking_lot_core tests r=Amanieu a=faern

This library could use more tests, to be more robust. This was one of the things pointed out in the review of the integration into std in rust-lang/rust#56410

`WTF::ParkingLot` has a number of tests we can take inspiration from. And this is somewhat of a port of some of those tests. However, when I ported it 1:1 I found a race condition, so I had to implement the semaphore a bit differently.

I also got away without the tests relying on a working mutex or condvar implementation. Because we can't make the `parking_lot_core` tests depend on the higher level `parking_lot`, nor do we want to depend on locking primitives in std if we aim to become the base for those implementations one day.

Co-authored-by: Linus Färnstrand <[email protected]>

core/src/parking_lot.rs

@@ -1389,3 +1389,276 @@ mod deadlock_impl {
         cycles.iter().cloned().collect()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{ThreadData, DEFAULT_PARK_TOKEN, DEFAULT_UNPARK_TOKEN};
+    use std::{
+        ptr,
+        sync::{
+            atomic::{AtomicIsize, AtomicPtr, AtomicUsize, Ordering},
+            Arc,
+        },
+        thread,
+        time::Duration,
+    };
+
+    /// Calls a closure for every `ThreadData` currently parked on a given key
+    fn for_each(key: usize, mut f: impl FnMut(&ThreadData)) {
+        let bucket = super::lock_bucket(key);
+
+        let mut current: *const ThreadData = bucket.queue_head.get();
+        while !current.is_null() {
+            let current_ref = unsafe { &*current };
+            if current_ref.key.load(Ordering::Relaxed) == key {
+                f(current_ref);
+            }
+            current = current_ref.next_in_queue.get();
+        }
+
+        // SAFETY: We hold the lock here, as required
+        unsafe { bucket.mutex.unlock() };
+    }
+
+    macro_rules! test {
+        ( $( $name:ident(
+            repeats: $repeats:expr,
+            latches: $latches:expr,
+            delay: $delay:expr,
+            threads: $threads:expr,
+            single_unparks: $single_unparks:expr);
+        )* ) => {
+            $(#[test]
+            fn $name() {
+                let delay = Duration::from_micros($delay);
+                for _ in 0..$repeats {
+                    run_parking_test($latches, delay, $threads, $single_unparks);
+                }
+            })*
+        };
+    }
+
+    test! {
+        unpark_all_one_fast(
+            repeats: 10000, latches: 1, delay: 0, threads: 1, single_unparks: 0
+        );
+        unpark_all_hundred_fast(
+            repeats: 100, latches: 1, delay: 0, threads: 100, single_unparks: 0
+        );
+        unpark_one_one_fast(
+            repeats: 1000, latches: 1, delay: 0, threads: 1, single_unparks: 1
+        );
+        unpark_one_hundred_fast(
+            repeats: 20, latches: 1, delay: 0, threads: 100, single_unparks: 100
+        );
+        unpark_one_fifty_then_fifty_all_fast(
+            repeats: 50, latches: 1, delay: 0, threads: 100, single_unparks: 50
+        );
+        unpark_all_one(
+            repeats: 100, latches: 1, delay: 10000, threads: 1, single_unparks: 0
+        );
+        unpark_all_hundred(
+            repeats: 100, latches: 1, delay: 10000, threads: 100, single_unparks: 0
+        );
+        unpark_one_one(
+            repeats: 10, latches: 1, delay: 10000, threads: 1, single_unparks: 1
+        );
+        unpark_one_fifty(
+            repeats: 1, latches: 1, delay: 10000, threads: 50, single_unparks: 50
+        );
+        unpark_one_fifty_then_fifty_all(
+            repeats: 2, latches: 1, delay: 10000, threads: 100, single_unparks: 50
+        );
+        hundred_unpark_all_one_fast(
+            repeats: 100, latches: 100, delay: 0, threads: 1, single_unparks: 0
+        );
+        hundred_unpark_all_one(
+            repeats: 1, latches: 100, delay: 10000, threads: 1, single_unparks: 0
+        );
+    }
+
+    fn run_parking_test(
+        num_latches: usize,
+        delay: Duration,
+        num_threads: usize,
+        num_single_unparks: usize,
+    ) {
+        let mut tests = Vec::with_capacity(num_latches);
+
+        for _ in 0..num_latches {
+            let test = Arc::new(SingleLatchTest::new(num_threads));
+            let mut threads = Vec::with_capacity(num_threads);
+            for _ in 0..num_threads {
+                let test = test.clone();
+                threads.push(thread::spawn(move || test.run()));
+            }
+            tests.push((test, threads));
+        }
+
+        for unpark_index in 0..num_single_unparks {
+            thread::sleep(delay);
+            for (test, _) in &tests {
+                test.unpark_one(unpark_index);
+            }
+        }
+
+        for (test, threads) in tests {
+            test.finish(num_single_unparks);
+            for thread in threads {
+                thread.join().expect("Test thread panic");
+            }
+        }
+    }
+
+    struct SingleLatchTest {
+        semaphore: AtomicIsize,
+        num_awake: AtomicUsize,
+        /// Holds the pointer to the last *unprocessed* woken up thread.
+        last_awoken: AtomicPtr<ThreadData>,
+        /// Total number of threads participating in this test.
+        num_threads: usize,
+    }
+
+    impl SingleLatchTest {
+        pub fn new(num_threads: usize) -> Self {
+            Self {
+                // This implements a fair (FIFO) semaphore, and it starts out unavailable.
+                semaphore: AtomicIsize::new(0),
+                num_awake: AtomicUsize::new(0),
+                last_awoken: AtomicPtr::new(ptr::null_mut()),
+                num_threads,
+            }
+        }
+
+        pub fn run(&self) {
+            // Get one slot from the semaphore
+            self.down();
+
+            // Report back to the test verification code that this thread woke up
+            let this_thread_ptr = super::with_thread_data(|t| t as *const _ as *mut _);
+            self.last_awoken.store(this_thread_ptr, Ordering::SeqCst);
+            self.num_awake.fetch_add(1, Ordering::SeqCst);
+        }
+
+        pub fn unpark_one(&self, single_unpark_index: usize) {
+            // last_awoken should be null at all times except between self.up() and at the bottom
+            // of this method where it's reset to null again
+            assert!(self.last_awoken.load(Ordering::SeqCst).is_null());
+
+            let mut queue: Vec<*mut ThreadData> = Vec::with_capacity(self.num_threads);
+            for_each(self.semaphore_addr(), |thread_data| {
+                queue.push(thread_data as *const _ as *mut _);
+            });
+            assert!(queue.len() <= self.num_threads - single_unpark_index);
+
+            let num_awake_before_up = self.num_awake.load(Ordering::SeqCst);
+
+            self.up();
+
+            // Wait for a parked thread to wake up and update num_awake + last_awoken.
+            while self.num_awake.load(Ordering::SeqCst) != num_awake_before_up + 1 {
+                thread::yield_now();
+            }
+
+            // At this point the other thread should have set last_awoken inside the run() method
+            let last_awoken = self.last_awoken.load(Ordering::SeqCst);
+            assert!(!last_awoken.is_null());
+            if !queue.is_empty() && queue[0] != last_awoken {
+                panic!(
+                    "Woke up wrong thread:\n\tqueue: {:?}\n\tlast awoken: {:?}",
+                    queue, last_awoken
+                );
+            }
+            self.last_awoken.store(ptr::null_mut(), Ordering::SeqCst);
+        }
+
+        pub fn finish(&self, num_single_unparks: usize) {
+            // The amount of threads not unparked via unpark_one
+            let mut num_threads_left = self.num_threads.checked_sub(num_single_unparks).unwrap();
+
+            // Wake remaining threads up with unpark_all. Has to be in a loop, because there might
+            // still be threads that has not yet parked.
+            while num_threads_left > 0 {
+                let mut num_waiting_on_address = 0;
+                for_each(self.semaphore_addr(), |_thread_data| {
+                    num_waiting_on_address += 1;
+                });
+                assert!(num_waiting_on_address <= num_threads_left);
+
+                let num_awake_before_unpark = self.num_awake.load(Ordering::SeqCst);
+
+                let num_unparked =
+                    unsafe { super::unpark_all(self.semaphore_addr(), DEFAULT_UNPARK_TOKEN) };
+                assert!(num_unparked >= num_waiting_on_address);
+                assert!(num_unparked <= num_threads_left);
+
+                // Wait for all unparked threads to wake up and update num_awake + last_awoken.
+                while self.num_awake.load(Ordering::SeqCst)
+                    != num_awake_before_unpark + num_unparked
+                {
+                    thread::yield_now()
+                }
+
+                num_threads_left = num_threads_left.checked_sub(num_unparked).unwrap();
+            }
+            // By now, all threads should have been woken up
+            assert_eq!(self.num_awake.load(Ordering::SeqCst), self.num_threads);
+
+            // Make sure no thread is parked on our semaphore address
+            let mut num_waiting_on_address = 0;
+            for_each(self.semaphore_addr(), |_thread_data| {
+                num_waiting_on_address += 1;
+            });
+            assert_eq!(num_waiting_on_address, 0);
+        }
+
+        pub fn down(&self) {
+            let old_semaphore_value = self.semaphore.fetch_sub(1, Ordering::SeqCst);
+
+            if old_semaphore_value > 0 {
+                // We acquired the semaphore. Done.
+                return;
+            }
+
+            // We need to wait.
+            let validate = || true;
+            let before_sleep = || {};
+            let timed_out = |_, _| {};
+            unsafe {
+                super::park(
+                    self.semaphore_addr(),
+                    validate,
+                    before_sleep,
+                    timed_out,
+                    DEFAULT_PARK_TOKEN,
+                    None,
+                );
+            }
+        }
+
+        pub fn up(&self) {
+            let old_semaphore_value = self.semaphore.fetch_add(1, Ordering::SeqCst);
+
+            // Check if anyone was waiting on the semaphore. If they were, then pass ownership to them.
+            if old_semaphore_value < 0 {
+                // We need to continue until we have actually unparked someone. It might be that
+                // the thread we want to pass ownership to has decremented the semaphore counter,
+                // but not yet parked.
+                loop {
+                    match unsafe {
+                        super::unpark_one(self.semaphore_addr(), |_| DEFAULT_UNPARK_TOKEN)
+                            .unparked_threads
+                    } {
+                        1 => break,
+                        0 => (),
+                        i => panic!("Should not wake up {} threads", i),
+                    }
+                }
+            }
+        }
+
+        fn semaphore_addr(&self) -> usize {
+            &self.semaphore as *const _ as usize
+        }
+    }
+}