static_locks 0.1.0

// Copyright 2016 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.
use parking_lot::{
    lock_api::{
        RawMutex as _,
        RawMutexFair as _,
        RawMutexTimed as _,
    },
    RawMutex,
};

use core::{
    cell::UnsafeCell,
    fmt,
    mem,
    ops::{Deref, DerefMut},
    marker::PhantomData,
    time::Duration,
};
use std::time::Instant;

#[cfg(feature = "owning_ref_support")]
use owning_ref::StableAddress;

#[cfg(feature = "serde_support")]
use serde::{Deserialize, Deserializer, Serialize, Serializer};

/// A mutual exclusion primitive useful for protecting shared data
///
/// This mutex will block threads waiting for the lock to become available. The
/// mutex can also be statically initialized or created via a `new`
/// constructor. Each mutex has a type parameter which represents the data that
/// it is protecting. The data can only be accessed through the RAII guards
/// returned from `lock` and `try_lock`, which guarantees that the data is only
/// ever accessed when the mutex is locked.
pub struct Mutex<T: ?Sized> {
    raw: RawMutex,
    data: UnsafeCell<T>,
}

unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}

impl<T> Mutex<T> {
    /// Creates a new mutex in an unlocked state ready for use.
    #[inline]
    pub const fn new(val: T) -> Mutex<T> {
        Mutex {
            raw: RawMutex::INIT,
            data: UnsafeCell::new(val),
        }
    }

    /// Consumes this mutex, returning the underlying data.
    #[inline]
    pub fn into_inner(self) -> T {
        self.data.into_inner()
    }
}

impl<T: ?Sized> Mutex<T> {
    /// # Safety
    ///
    /// The lock must be held when calling this method.
    #[inline]
    unsafe fn guard(&self) -> MutexGuard<'_, T> {
        MutexGuard {
            mutex: self,
            marker: PhantomData,
        }
    }

    /// Acquires a mutex, blocking the current thread until it is able to do so.
    ///
    /// This function will block the local thread until it is available to acquire
    /// the mutex. Upon returning, the thread is the only thread with the mutex
    /// held. An RAII guard is returned to allow scoped unlock of the lock. When
    /// the guard goes out of scope, the mutex will be unlocked.
    ///
    /// Attempts to lock a mutex in the thread which already holds the lock will
    /// result in a deadlock.
    #[inline]
    pub fn lock(&self) -> MutexGuard<'_, T> {
        self.raw.lock();
        // SAFETY: The lock is held, as required.
        unsafe { self.guard() }
    }

    /// Attempts to acquire this lock.
    ///
    /// If the lock could not be acquired at this time, then `None` is returned.
    /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
    /// guard is dropped.
    ///
    /// This function does not block.
    #[inline]
    pub fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
        if self.raw.try_lock() {
            // SAFETY: The lock is held, as required.
            Some(unsafe { self.guard() })
        } else {
            None
        }
    }

    /// Returns a mutable reference to the underlying data.
    ///
    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
    /// take place---the mutable borrow statically guarantees no locks exist.
    #[inline]
    pub fn get_mut(&mut self) -> &mut T {
        unsafe { &mut *self.data.get() }
    }

    /// Forcibly unlocks the mutex.
    ///
    /// This is useful when combined with `mem::forget` to hold a lock without
    /// the need to maintain a `MutexGuard` object alive, for example when
    /// dealing with FFI.
    ///
    /// # Safety
    ///
    /// This method must only be called if the current thread logically owns a
    /// `MutexGuard` but that guard has be discarded using `mem::forget`.
    /// Behavior is undefined if a mutex is unlocked when not locked.
    #[inline]
    pub unsafe fn force_unlock(&self) {
        self.raw.unlock();
    }

    /// Returns the underlying raw mutex object.
    ///
    /// Note that you will most likely need to import the `RawMutex` trait from
    /// `lock_api` to be able to call functions on the raw mutex.
    ///
    /// # Safety
    ///
    /// This method is unsafe because it allows unlocking a mutex while
    /// still holding a reference to a `MutexGuard`.
    #[inline]
    pub unsafe fn raw(&self) -> &RawMutex {
        &self.raw
    }
}

impl<T: ?Sized> Mutex<T> {
    /// Forcibly unlocks the mutex using a fair unlock procotol.
    ///
    /// This is useful when combined with `mem::forget` to hold a lock without
    /// the need to maintain a `MutexGuard` object alive, for example when
    /// dealing with FFI.
    ///
    /// # Safety
    ///
    /// This method must only be called if the current thread logically owns a
    /// `MutexGuard` but that guard has be discarded using `mem::forget`.
    /// Behavior is undefined if a mutex is unlocked when not locked.
    #[inline]
    pub unsafe fn force_unlock_fair(&self) {
        self.raw.unlock_fair();
    }
}

impl<T: ?Sized> Mutex<T> {
    /// Attempts to acquire this lock until a timeout is reached.
    ///
    /// If the lock could not be acquired before the timeout expired, then
    /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
    /// be unlocked when the guard is dropped.
    #[inline]
    pub fn try_lock_for(&self, timeout: Duration) -> Option<MutexGuard<'_, T>> {
        if self.raw.try_lock_for(timeout) {
            // SAFETY: The lock is held, as required.
            Some(unsafe { self.guard() })
        } else {
            None
        }
    }

    /// Attempts to acquire this lock until a timeout is reached.
    ///
    /// If the lock could not be acquired before the timeout expired, then
    /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
    /// be unlocked when the guard is dropped.
    #[inline]
    pub fn try_lock_until(&self, timeout: Instant) -> Option<MutexGuard<'_, T>> {
        if self.raw.try_lock_until(timeout) {
            // SAFETY: The lock is held, as required.
            Some(unsafe { self.guard() })
        } else {
            None
        }
    }
}

impl<T: ?Sized + Default> Default for Mutex<T> {
    #[inline]
    fn default() -> Mutex<T> {
        Mutex::new(Default::default())
    }
}

impl<T> From<T> for Mutex<T> {
    #[inline]
    fn from(t: T) -> Mutex<T> {
        Mutex::new(t)
    }
}

impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.try_lock() {
            Some(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
            None => {
                struct LockedPlaceholder;
                impl fmt::Debug for LockedPlaceholder {
                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                        f.write_str("<locked>")
                    }
                }

                f.debug_struct("Mutex")
                    .field("data", &LockedPlaceholder)
                    .finish()
            }
        }
    }
}

// Copied and modified from serde
#[cfg(feature = "serde_support")]
impl<T> Serialize for Mutex<T>
where
    T: Serialize + ?Sized,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        self.lock().serialize(serializer)
    }
}

#[cfg(feature = "serde_support")]
impl<'de, T> Deserialize<'de> for Mutex<T>
where
    T: Deserialize<'de> + ?Sized,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        Deserialize::deserialize(deserializer).map(Mutex::new)
    }
}

/// An RAII implementation of a "scoped lock" of a mutex. When this structure is
/// dropped (falls out of scope), the lock will be unlocked.
///
/// The data protected by the mutex can be accessed through this guard via its
/// `Deref` and `DerefMut` implementations.
#[must_use = "if unused the Mutex will immediately unlock"]
pub struct MutexGuard<'a, T: ?Sized> {
    mutex: &'a Mutex<T>,
    marker: PhantomData<(&'a mut T, *mut ())>,
}

unsafe impl<'a, T: ?Sized + Sync + 'a> Sync for MutexGuard<'a, T> {}

impl<'a, T: ?Sized + 'a> MutexGuard<'a, T> {
    /// Returns a reference to the original `Mutex` object.
    pub fn mutex(s: &Self) -> &'a Mutex<T> {
        s.mutex
    }

    /// Makes a new `MappedMutexGuard` for a component of the locked data.
    ///
    /// This operation cannot fail as the `MutexGuard` passed
    /// in already locked the mutex.
    ///
    /// This is an associated function that needs to be
    /// used as `MutexGuard::map(...)`. A method would interfere with methods of
    /// the same name on the contents of the locked data.
    #[inline]
    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedMutexGuard<'a, U>
    where
        F: FnOnce(&mut T) -> &mut U,
    {
        let raw = &s.mutex.raw;
        let data = f(unsafe { &mut *s.mutex.data.get() });
        mem::forget(s);
        MappedMutexGuard {
            raw,
            data,
            marker: PhantomData,
        }
    }

    /// Attempts to make a new `MappedMutexGuard` for a component of the
    /// locked data. The original guard is returned if the closure returns `None`.
    ///
    /// This operation cannot fail as the `MutexGuard` passed
    /// in already locked the mutex.
    ///
    /// This is an associated function that needs to be
    /// used as `MutexGuard::try_map(...)`. A method would interfere with methods of
    /// the same name on the contents of the locked data.
    #[inline]
    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, U>, Self>
    where
        F: FnOnce(&mut T) -> Option<&mut U>,
    {
        let raw = &s.mutex.raw;
        let data = match f(unsafe { &mut *s.mutex.data.get() }) {
            Some(data) => data,
            None => return Err(s),
        };
        mem::forget(s);
        Ok(MappedMutexGuard {
            raw,
            data,
            marker: PhantomData,
        })
    }

    /// Temporarily unlocks the mutex to execute the given function.
    ///
    /// This is safe because `&mut` guarantees that there exist no other
    /// references to the data protected by the mutex.
    #[inline]
    pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
    where
        F: FnOnce() -> U,
    {
        s.mutex.raw.unlock();
        defer!(s.mutex.raw.lock());
        f()
    }
}

impl<'a, T: ?Sized + 'a> MutexGuard<'a, T> {
    /// Unlocks the mutex using a fair unlock protocol.
    ///
    /// By default, mutexes are unfair and allow the current thread to re-lock
    /// the mutex before another has the chance to acquire the lock, even if
    /// that thread has been blocked on the mutex for a long time. This is the
    /// default because it allows much higher throughput as it avoids forcing a
    /// context switch on every mutex unlock. This can result in one thread
    /// acquiring a mutex many more times than other threads.
    ///
    /// However in some cases it can be beneficial to ensure fairness by forcing
    /// the lock to pass on to a waiting thread if there is one. This is done by
    /// using this method instead of dropping the `MutexGuard` normally.
    #[inline]
    pub fn unlock_fair(s: Self) {
        s.mutex.raw.unlock_fair();
        mem::forget(s);
    }

    /// Temporarily unlocks the mutex to execute the given function.
    ///
    /// The mutex is unlocked using a fair unlock protocol.
    ///
    /// This is safe because `&mut` guarantees that there exist no other
    /// references to the data protected by the mutex.
    #[inline]
    pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
    where
        F: FnOnce() -> U,
    {
        s.mutex.raw.unlock_fair();
        defer!(s.mutex.raw.lock());
        f()
    }

    /// Temporarily yields the mutex to a waiting thread if there is one.
    ///
    /// This method is functionally equivalent to calling `unlock_fair` followed
    /// by `lock`, however it can be much more efficient in the case where there
    /// are no waiting threads.
    #[inline]
    pub fn bump(s: &mut Self) {
        s.mutex.raw.bump();
    }
}

impl<'a, T: ?Sized + 'a> Deref for MutexGuard<'a, T> {
    type Target = T;
    #[inline]
    fn deref(&self) -> &T {
        unsafe { &*self.mutex.data.get() }
    }
}

impl<'a, T: ?Sized + 'a> DerefMut for MutexGuard<'a, T> {
    #[inline]
    fn deref_mut(&mut self) -> &mut T {
        unsafe { &mut *self.mutex.data.get() }
    }
}

impl<'a, T: ?Sized + 'a> Drop for MutexGuard<'a, T> {
    #[inline]
    fn drop(&mut self) {
        self.mutex.raw.unlock();
    }
}

impl<'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for MutexGuard<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(&**self, f)
    }
}

impl<'a, T: fmt::Display + ?Sized + 'a> fmt::Display for MutexGuard<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        (**self).fmt(f)
    }
}

#[cfg(feature = "owning_ref_support")]
unsafe impl<'a, T: ?Sized + 'a> StableAddress for MutexGuard<'a, T> {}

/// An RAII mutex guard returned by `MutexGuard::map`, which can point to a
/// subfield of the protected data.
///
/// The main difference between `MappedMutexGuard` and `MutexGuard` is that the
/// former doesn't support temporarily unlocking and re-locking, since that
/// could introduce soundness issues if the locked object is modified by another
/// thread.
#[must_use = "if unused the Mutex will immediately unlock"]
pub struct MappedMutexGuard<'a, T: ?Sized> {
    raw: &'a RawMutex,
    data: *mut T,
    marker: PhantomData<&'a mut T>,
}

unsafe impl<'a, T: ?Sized + Sync + 'a> Sync
    for MappedMutexGuard<'a, T>
{
}

impl<'a, T: ?Sized + 'a> MappedMutexGuard<'a, T> {
    /// Makes a new `MappedMutexGuard` for a component of the locked data.
    ///
    /// This operation cannot fail as the `MappedMutexGuard` passed
    /// in already locked the mutex.
    ///
    /// This is an associated function that needs to be
    /// used as `MappedMutexGuard::map(...)`. A method would interfere with methods of
    /// the same name on the contents of the locked data.
    #[inline]
    pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedMutexGuard<'a, U>
    where
        F: FnOnce(&mut T) -> &mut U,
    {
        let raw = s.raw;
        let data = f(unsafe { &mut *s.data });
        mem::forget(s);
        MappedMutexGuard {
            raw,
            data,
            marker: PhantomData,
        }
    }

    /// Attempts to make a new `MappedMutexGuard` for a component of the
    /// locked data. The original guard is returned if the closure returns `None`.
    ///
    /// This operation cannot fail as the `MappedMutexGuard` passed
    /// in already locked the mutex.
    ///
    /// This is an associated function that needs to be
    /// used as `MappedMutexGuard::try_map(...)`. A method would interfere with methods of
    /// the same name on the contents of the locked data.
    #[inline]
    pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, U>, Self>
    where
        F: FnOnce(&mut T) -> Option<&mut U>,
    {
        let raw = s.raw;
        let data = match f(unsafe { &mut *s.data }) {
            Some(data) => data,
            None => return Err(s),
        };
        mem::forget(s);
        Ok(MappedMutexGuard {
            raw,
            data,
            marker: PhantomData,
        })
    }
}

impl<'a, T: ?Sized + 'a> MappedMutexGuard<'a, T> {
    /// Unlocks the mutex using a fair unlock protocol.
    ///
    /// By default, mutexes are unfair and allow the current thread to re-lock
    /// the mutex before another has the chance to acquire the lock, even if
    /// that thread has been blocked on the mutex for a long time. This is the
    /// default because it allows much higher throughput as it avoids forcing a
    /// context switch on every mutex unlock. This can result in one thread
    /// acquiring a mutex many more times than other threads.
    ///
    /// However in some cases it can be beneficial to ensure fairness by forcing
    /// the lock to pass on to a waiting thread if there is one. This is done by
    /// using this method instead of dropping the `MutexGuard` normally.
    #[inline]
    pub fn unlock_fair(s: Self) {
        s.raw.unlock_fair();
        mem::forget(s);
    }
}

impl<'a, T: ?Sized + 'a> Deref for MappedMutexGuard<'a, T> {
    type Target = T;
    #[inline]
    fn deref(&self) -> &T {
        unsafe { &*self.data }
    }
}

impl<'a, T: ?Sized + 'a> DerefMut for MappedMutexGuard<'a, T> {
    #[inline]
    fn deref_mut(&mut self) -> &mut T {
        unsafe { &mut *self.data }
    }
}

impl<'a, T: ?Sized + 'a> Drop for MappedMutexGuard<'a, T> {
    #[inline]
    fn drop(&mut self) {
        self.raw.unlock();
    }
}

impl<'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for MappedMutexGuard<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(&**self, f)
    }
}

impl<'a, T: fmt::Display + ?Sized + 'a> fmt::Display
    for MappedMutexGuard<'a, T>
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        (**self).fmt(f)
    }
}

#[cfg(feature = "owning_ref_support")]
unsafe impl<'a, T: ?Sized + 'a> StableAddress for MappedMutexGuard<'a, T> {}

#[cfg(test)]
mod tests {
    use crate::Mutex;
    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::sync::mpsc::channel;
    use std::sync::Arc;
    use std::thread;

    #[cfg(feature = "serde_support")]
    use bincode::{deserialize, serialize};

    #[derive(Eq, PartialEq, Debug)]
    struct NonCopy(i32);

    #[test]
    fn smoke() {
        let m = Mutex::new(());
        drop(m.lock());
        drop(m.lock());
    }

    #[test]
    fn lots_and_lots() {
        const J: u32 = 1000;
        const K: u32 = 3;

        let m = Arc::new(Mutex::new(0));

        fn inc(m: &Mutex<u32>) {
            for _ in 0..J {
                *m.lock() += 1;
            }
        }

        let (tx, rx) = channel();
        for _ in 0..K {
            let tx2 = tx.clone();
            let m2 = m.clone();
            thread::spawn(move || {
                inc(&m2);
                tx2.send(()).unwrap();
            });
            let tx2 = tx.clone();
            let m2 = m.clone();
            thread::spawn(move || {
                inc(&m2);
                tx2.send(()).unwrap();
            });
        }

        drop(tx);
        for _ in 0..2 * K {
            rx.recv().unwrap();
        }
        assert_eq!(*m.lock(), J * K * 2);
    }

    #[test]
    fn try_lock() {
        let m = Mutex::new(());
        *m.try_lock().unwrap() = ();
    }

    #[test]
    fn test_into_inner() {
        let m = Mutex::new(NonCopy(10));
        assert_eq!(m.into_inner(), NonCopy(10));
    }

    #[test]
    fn test_into_inner_drop() {
        struct Foo(Arc<AtomicUsize>);
        impl Drop for Foo {
            fn drop(&mut self) {
                self.0.fetch_add(1, Ordering::SeqCst);
            }
        }
        let num_drops = Arc::new(AtomicUsize::new(0));
        let m = Mutex::new(Foo(num_drops.clone()));
        assert_eq!(num_drops.load(Ordering::SeqCst), 0);
        {
            let _inner = m.into_inner();
            assert_eq!(num_drops.load(Ordering::SeqCst), 0);
        }
        assert_eq!(num_drops.load(Ordering::SeqCst), 1);
    }

    #[test]
    fn test_get_mut() {
        let mut m = Mutex::new(NonCopy(10));
        *m.get_mut() = NonCopy(20);
        assert_eq!(m.into_inner(), NonCopy(20));
    }

    #[test]
    fn test_mutex_arc_nested() {
        // Tests nested mutexes and access
        // to underlying data.
        let arc = Arc::new(Mutex::new(1));
        let arc2 = Arc::new(Mutex::new(arc));
        let (tx, rx) = channel();
        let _t = thread::spawn(move || {
            let lock = arc2.lock();
            let lock2 = lock.lock();
            assert_eq!(*lock2, 1);
            tx.send(()).unwrap();
        });
        rx.recv().unwrap();
    }

    #[test]
    fn test_mutex_arc_access_in_unwind() {
        let arc = Arc::new(Mutex::new(1));
        let arc2 = arc.clone();
        let _ = thread::spawn(move || {
            struct Unwinder {
                i: Arc<Mutex<i32>>,
            }
            impl Drop for Unwinder {
                fn drop(&mut self) {
                    *self.i.lock() += 1;
                }
            }
            let _u = Unwinder { i: arc2 };
            panic!();
        })
        .join();
        let lock = arc.lock();
        assert_eq!(*lock, 2);
    }

    #[test]
    fn test_mutex_unsized() {
        let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]);
        {
            let b = &mut *mutex.lock();
            b[0] = 4;
            b[2] = 5;
        }
        let comp: &[i32] = &[4, 2, 5];
        assert_eq!(&*mutex.lock(), comp);
    }

    #[test]
    fn test_mutexguard_sync() {
        fn sync<T: Sync>(_: T) {}

        let mutex = Mutex::new(());
        sync(mutex.lock());
    }

    #[test]
    fn test_mutex_debug() {
        let mutex = Mutex::new(vec![0u8, 10]);

        assert_eq!(format!("{:?}", mutex), "Mutex { data: [0, 10] }");
        let _lock = mutex.lock();
        assert_eq!(format!("{:?}", mutex), "Mutex { data: <locked> }");
    }

    #[cfg(feature = "serde_support")]
    #[test]
    fn test_serde() {
        let contents: Vec<u8> = vec![0, 1, 2];
        let mutex = Mutex::new(contents.clone());

        let serialized = serialize(&mutex).unwrap();
        let deserialized: Mutex<Vec<u8>> = deserialize(&serialized).unwrap();

        assert_eq!(*(mutex.lock()), *(deserialized.lock()));
        assert_eq!(contents, *(deserialized.lock()));
    }
}