parking_lot 0.12.1

//! \[Experimental\] Deadlock detection
//!
//! This feature is optional and can be enabled via the `deadlock_detection` feature flag.
//!
//! # Example
//!
//! ```
//! #[cfg(feature = "deadlock_detection")]
//! { // only for #[cfg]
//! use std::thread;
//! use std::time::Duration;
//! use parking_lot::deadlock;
//!
//! // Create a background thread which checks for deadlocks every 10s
//! thread::spawn(move || {
//!     loop {
//!         thread::sleep(Duration::from_secs(10));
//!         let deadlocks = deadlock::check_deadlock();
//!         if deadlocks.is_empty() {
//!             continue;
//!         }
//!
//!         println!("{} deadlocks detected", deadlocks.len());
//!         for (i, threads) in deadlocks.iter().enumerate() {
//!             println!("Deadlock #{}", i);
//!             for t in threads {
//!                 println!("Thread Id {:#?}", t.thread_id());
//!                 println!("{:#?}", t.backtrace());
//!             }
//!         }
//!     }
//! });
//! } // only for #[cfg]
//! ```

#[cfg(feature = "deadlock_detection")]
pub use parking_lot_core::deadlock::check_deadlock;
pub(crate) use parking_lot_core::deadlock::{acquire_resource, release_resource};

#[cfg(test)]
#[cfg(feature = "deadlock_detection")]
mod tests {
    use crate::{Mutex, ReentrantMutex, RwLock};
    use std::sync::{Arc, Barrier};
    use std::thread::{self, sleep};
    use std::time::Duration;

    // We need to serialize these tests since deadlock detection uses global state
    static DEADLOCK_DETECTION_LOCK: Mutex<()> = crate::const_mutex(());

    fn check_deadlock() -> bool {
        use parking_lot_core::deadlock::check_deadlock;
        !check_deadlock().is_empty()
    }

    #[test]
    fn test_mutex_deadlock() {
        let _guard = DEADLOCK_DETECTION_LOCK.lock();

        let m1: Arc<Mutex<()>> = Default::default();
        let m2: Arc<Mutex<()>> = Default::default();
        let m3: Arc<Mutex<()>> = Default::default();
        let b = Arc::new(Barrier::new(4));

        let m1_ = m1.clone();
        let m2_ = m2.clone();
        let m3_ = m3.clone();
        let b1 = b.clone();
        let b2 = b.clone();
        let b3 = b.clone();

        assert!(!check_deadlock());

        let _t1 = thread::spawn(move || {
            let _g = m1.lock();
            b1.wait();
            let _ = m2_.lock();
        });

        let _t2 = thread::spawn(move || {
            let _g = m2.lock();
            b2.wait();
            let _ = m3_.lock();
        });

        let _t3 = thread::spawn(move || {
            let _g = m3.lock();
            b3.wait();
            let _ = m1_.lock();
        });

        assert!(!check_deadlock());

        b.wait();
        sleep(Duration::from_millis(50));
        assert!(check_deadlock());

        assert!(!check_deadlock());
    }

    #[test]
    fn test_mutex_deadlock_reentrant() {
        let _guard = DEADLOCK_DETECTION_LOCK.lock();

        let m1: Arc<Mutex<()>> = Default::default();

        assert!(!check_deadlock());

        let _t1 = thread::spawn(move || {
            let _g = m1.lock();
            let _ = m1.lock();
        });

        sleep(Duration::from_millis(50));
        assert!(check_deadlock());

        assert!(!check_deadlock());
    }

    #[test]
    fn test_remutex_deadlock() {
        let _guard = DEADLOCK_DETECTION_LOCK.lock();

        let m1: Arc<ReentrantMutex<()>> = Default::default();
        let m2: Arc<ReentrantMutex<()>> = Default::default();
        let m3: Arc<ReentrantMutex<()>> = Default::default();
        let b = Arc::new(Barrier::new(4));

        let m1_ = m1.clone();
        let m2_ = m2.clone();
        let m3_ = m3.clone();
        let b1 = b.clone();
        let b2 = b.clone();
        let b3 = b.clone();

        assert!(!check_deadlock());

        let _t1 = thread::spawn(move || {
            let _g = m1.lock();
            let _g = m1.lock();
            b1.wait();
            let _ = m2_.lock();
        });

        let _t2 = thread::spawn(move || {
            let _g = m2.lock();
            let _g = m2.lock();
            b2.wait();
            let _ = m3_.lock();
        });

        let _t3 = thread::spawn(move || {
            let _g = m3.lock();
            let _g = m3.lock();
            b3.wait();
            let _ = m1_.lock();
        });

        assert!(!check_deadlock());

        b.wait();
        sleep(Duration::from_millis(50));
        assert!(check_deadlock());

        assert!(!check_deadlock());
    }

    #[test]
    fn test_rwlock_deadlock() {
        let _guard = DEADLOCK_DETECTION_LOCK.lock();

        let m1: Arc<RwLock<()>> = Default::default();
        let m2: Arc<RwLock<()>> = Default::default();
        let m3: Arc<RwLock<()>> = Default::default();
        let b = Arc::new(Barrier::new(4));

        let m1_ = m1.clone();
        let m2_ = m2.clone();
        let m3_ = m3.clone();
        let b1 = b.clone();
        let b2 = b.clone();
        let b3 = b.clone();

        assert!(!check_deadlock());

        let _t1 = thread::spawn(move || {
            let _g = m1.read();
            b1.wait();
            let _g = m2_.write();
        });

        let _t2 = thread::spawn(move || {
            let _g = m2.read();
            b2.wait();
            let _g = m3_.write();
        });

        let _t3 = thread::spawn(move || {
            let _g = m3.read();
            b3.wait();
            let _ = m1_.write();
        });

        assert!(!check_deadlock());

        b.wait();
        sleep(Duration::from_millis(50));
        assert!(check_deadlock());

        assert!(!check_deadlock());
    }

    #[cfg(rwlock_deadlock_detection_not_supported)]
    #[test]
    fn test_rwlock_deadlock_reentrant() {
        let _guard = DEADLOCK_DETECTION_LOCK.lock();

        let m1: Arc<RwLock<()>> = Default::default();

        assert!(!check_deadlock());

        let _t1 = thread::spawn(move || {
            let _g = m1.read();
            let _ = m1.write();
        });

        sleep(Duration::from_millis(50));
        assert!(check_deadlock());

        assert!(!check_deadlock());
    }
}