1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
//! Sleep lock or mutex implementation.

use crate::{
    sleep_queue::SleepQueue,
    sync::Spinlock,
    task::{SleepKind, Task},
};
use core::{
    cell::UnsafeCell,
    fmt,
    future::Future,
    ops::{Deref, DerefMut},
    pin::Pin,
    task::{Context, Poll},
};

/// Inner sleep queue and lock state of Mutex.
struct MutexInner {
    /// If this mutex has been locked.
    locked: bool,
    /// The sleep queue of waiting tasks.
    sleep_queue: SleepQueue,
}

/// An async mutex.
///
/// The locking mechanism uses a FIFO wait queue to avoid starvation.
///
/// # Examples
///
/// ```
/// # ksched::task::spawn(async {
/// use ksched::sync::Mutex;
///
/// let m: Mutex<usize> = Mutex::new(1);
///
/// let mut guard = m.lock().await;
/// *guard = 2;
/// drop(guard);
///
/// let guard = m.lock().await;
/// assert_eq!(*guard, 2);
/// # });
/// # ksched::task::run();
/// ```
pub struct Mutex<T: ?Sized> {
    /// Guard towards status and waiting queue.
    inner: Spinlock<MutexInner>,

    /// The value inside the mutex.
    data: UnsafeCell<T>,
}

// Note that inner is already send and sync by [spin::Mutex]
unsafe impl<T: Send + ?Sized> Send for Mutex<T> {}
unsafe impl<T: Send + ?Sized> Sync for Mutex<T> {}

impl<T> Mutex<T> {
    /// Creates a new async mutex.
    ///
    /// # Examples
    ///
    /// ```
    /// use ksched::sync::Mutex;
    ///
    /// let mutex: Mutex<usize> = Mutex::new(0);
    /// ```
    pub const fn new(data: T) -> Mutex<T> {
        Mutex {
            inner: Spinlock::new(MutexInner {
                locked: false,
                sleep_queue: SleepQueue::new(),
            }),
            data: UnsafeCell::new(data),
        }
    }

    /// Consumes the mutex, returning the underlying data.
    ///
    /// # Examples
    ///
    /// ```
    /// use ksched::sync::Mutex;
    ///
    /// let mutex: Mutex<usize> = Mutex::new(10);
    /// assert_eq!(mutex.into_inner(), 10);
    /// ```
    pub fn into_inner(self) -> T {
        self.data.into_inner()
    }
}

impl<T: ?Sized> Mutex<T> {
    /// Acquire the mutex, which must be release manually by [`Self::release`]
    pub async fn acquire(&self) {
        struct Lock<'a, T: ?Sized>(&'a Mutex<T>);

        impl<'a, T: ?Sized> Future for Lock<'a, T> {
            type Output = ();

            fn poll(self: Pin<&mut Self>, ctx: &mut Context<'_>) -> Poll<Self::Output> {
                let mut inner = self.0.inner.lock();
                let result = if inner.locked {
                    Task::sleep_back(&mut inner.sleep_queue, SleepKind::Mutex, ctx);
                    Poll::Pending
                } else {
                    inner.locked = true;
                    Poll::Ready(())
                };
                result
            }
        }
        Lock(self).await
    }

    /// Unlock manually.
    pub unsafe fn release(&self) {
        let mut inner = self.inner.lock();
        debug_assert_eq!(inner.locked, true);
        Task::wakeup_front(&mut inner.sleep_queue);
        inner.locked = false;
    }

    /// Acquires the mutex.
    ///
    /// Since inserting current task to the wait queue requires memory
    /// allocation, this function may return [AllocError] on oom.
    /// Otherwise, returns a guard that releases the mutex when dropped.
    ///
    /// # Examples
    ///
    /// ```
    /// # ksched::task::spawn(async {
    /// use ksched::sync::Mutex;
    ///
    /// let mutex: Mutex<usize> = Mutex::new(10);
    /// let guard = mutex.lock().await;
    /// assert_eq!(*guard, 10);
    /// # });
    /// # ksched::task::run();
    /// ```
    #[inline]
    pub async fn lock(&self) -> MutexGuard<'_, T> {
        self.acquire().await;
        MutexGuard(self)
    }

    /// Attempts to acquire the mutex.
    ///
    /// If the mutex could not be acquired at this time, then [`None`] is returned. Otherwise, a
    /// guard is returned that releases the mutex when dropped.
    ///
    /// # Examples
    ///
    /// ```
    /// use ksched::sync::Mutex;
    ///
    /// let mutex = Mutex::new(10);
    /// if let Some(guard) = mutex.try_lock() {
    ///     assert_eq!(*guard, 10);
    /// }
    /// # ;
    /// ```
    #[inline]
    pub fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
        let mut g = self.inner.lock();
        if g.locked {
            None
        } else {
            g.locked = true;
            Some(MutexGuard(self))
        }
    }

    /// Returns a mutable reference to the underlying data.
    ///
    /// Since this call borrows the mutex mutably, no actual locking takes place -- the mutable
    /// borrow statically guarantees the mutex is not already acquired.
    ///
    /// # Examples
    ///
    /// ```
    /// # ksched::task::spawn(async {
    /// use ksched::sync::Mutex;
    ///
    /// let mut mutex: Mutex<usize> = Mutex::new(0);
    /// *mutex.get_mut() = 10;
    /// assert_eq!(*mutex.lock().await, 10);
    /// # });
    /// # ksched::task::run();
    /// ```
    pub fn get_mut(&mut self) -> &mut T {
        unsafe { &mut *self.data.get() }
    }
}

impl<T: fmt::Debug + ?Sized> fmt::Debug for Mutex<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        struct Locked;
        impl fmt::Debug for Locked {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                f.write_str("<locked>")
            }
        }

        match self.try_lock() {
            None => f.debug_struct("Mutex").field("data", &Locked).finish(),
            Some(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
        }
    }
}

impl<T> From<T> for Mutex<T> {
    fn from(val: T) -> Mutex<T> {
        Mutex::new(val)
    }
}

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

/// A guard that releases the mutex when dropped.
pub struct MutexGuard<'a, T: ?Sized>(&'a Mutex<T>);

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

impl<'a, T: ?Sized> MutexGuard<'a, T> {
    /// Returns a reference to the mutex a guard came from.
    ///
    /// # Examples
    ///
    /// ```
    /// # ksched::task::spawn(async {
    /// use ksched::sync::{Mutex, MutexGuard};
    ///
    /// let mutex = Mutex::new(10i32);
    /// let guard = mutex.lock().await;
    /// dbg!(MutexGuard::source(&guard));
    /// # }).unwrap();
    /// # ksched::task::run();
    /// ```
    pub fn source(guard: &MutexGuard<'a, T>) -> &'a Mutex<T> {
        guard.0
    }
}

impl<T: ?Sized> Drop for MutexGuard<'_, T> {
    fn drop(&mut self) {
        unsafe { self.0.release() }
    }
}

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

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

impl<T: ?Sized> Deref for MutexGuard<'_, T> {
    type Target = T;

    fn deref(&self) -> &T {
        unsafe { &*self.0.data.get() }
    }
}

impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
    fn deref_mut(&mut self) -> &mut T {
        unsafe { &mut *self.0.data.get() }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::task;
    use crate::tests::run_multi;
    use std::sync::Arc;

    #[test]
    fn test_mutex() {
        const N: usize = 100;
        const NCPU: usize = 4;
        let data: Arc<Mutex<usize>> = Arc::new(Mutex::new(0));
        for _i in 0..N {
            let data = data.clone();
            task::spawn(async move {
                let mut lk = data.lock().await;
                task::yield_now().await;
                *lk += 1;
                task::yield_now().await;
            })
            .unwrap();
        }
        run_multi(NCPU);
        let guard = data.try_lock().unwrap();
        assert_eq!(*guard, N);
    }
}