test: Multithreaded tests

src/mutex.rs

@@ -110,6 +110,8 @@ impl<T> DerefMut for MutexGuard<'_, T> {
 
 #[cfg(test)]
 mod tests {
+    use std::{hint::black_box, sync::Arc, thread};
+
     use super::*;
 
     #[test]
@@ -130,6 +132,19 @@ mod tests {
         assert_eq!(43, *guard)
     }
 
+    #[test]
+    fn multithreaded() {
+        let mutex = Arc::new(Mutex::new(()));
+        let thread = thread::spawn({
+            let mutex = mutex.clone();
+            move || {
+                black_box(mutex.lock().unwrap());
+            }
+        });
+        black_box(mutex.lock().unwrap());
+        thread.join().unwrap();
+    }
+
     #[test]
     #[should_panic(
         expected = "Tried to acquire lock with level 0 while a lock with level 0 is acquired. This is a violation of lock hierarchies which could lead to deadlocks."

src/rwlock.rs

@@ -144,6 +144,8 @@ impl<T> DerefMut for RwLockWriteGuard<'_, T> {
 
 #[cfg(test)]
 mod tests {
+    use std::{hint::black_box, sync::Arc, thread};
+
     use super::*;
 
     #[test]
@@ -168,6 +170,21 @@ mod tests {
         assert_eq!(43, *guard)
     }
 
+    #[test]
+    fn multithreaded() {
+        let mutex = Arc::new(RwLock::new(()));
+        let thread = thread::spawn({
+            let mutex = mutex.clone();
+            move || {
+                black_box(mutex.read().unwrap());
+                black_box(mutex.write().unwrap());
+            }
+        });
+        black_box(mutex.read().unwrap());
+        black_box(mutex.write().unwrap());
+        thread.join().unwrap();
+    }
+
     #[cfg(debug_assertions)]
     fn poisoned_lock() -> RwLock<()> {
         let mutex = RwLock::new(());