# mutex.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/spin-0.7.1/src/mutex.rs`.
Keywords: rust, rustlang, rust-lang

    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
    310
    311
    312
    313
    314
    315

    //! Locks that have the same behaviour as a mutex.
    //!
    //! The [`Mutex`] in the root of the crate, can be configured using the `ticket_mutex` feature.
    //! If it's enabled, [`TicketMutex`] and [`TicketMutexGuard`] will be re-exported as [`Mutex`]
    //! and [`MutexGuard`], otherwise the [`SpinMutex`] and guard will be re-exported.
    //!
    //! `ticket_mutex` is enabled by default.
    //!
    //! [`Mutex`]: ../struct.Mutex.html
    //! [`MutexGuard`]: ../struct.MutexGuard.html
    //! [`TicketMutex`]: ./struct.TicketMutex.html
    //! [`TicketMutexGuard`]: ./struct.TicketMutexGuard.html
    //! [`SpinMutex`]: ./struct.SpinMutex.html

    mod spin;
    pub use self::spin::*;

    mod ticket;
    pub use self::ticket::*;

    use core::{
        fmt,
        ops::{Deref, DerefMut},
    };

    #[cfg(feature = "ticket_mutex")]
    type InnerMutex<T> = TicketMutex<T>;
    #[cfg(feature = "ticket_mutex")]
    type InnerMutexGuard<'a, T> = TicketMutexGuard<'a, T>;

    #[cfg(not(feature = "ticket_mutex"))]
    type InnerMutex<T> = SpinMutex<T>;
    #[cfg(not(feature = "ticket_mutex"))]
    type InnerMutexGuard<'a, T> = SpinMutexGuard<'a, T>;

    /// A spin-based lock providing mutually exclusive access to data.
    ///
    /// The implementation uses either a [`TicketMutex`] or a regular [`SpinMutex`] depending on whether the `ticket_mutex`
    /// feature flag is enabled.
    ///
    /// # Example
    ///
    /// ```
    /// use spin;
    ///
    /// let lock = spin::Mutex::new(0);
    ///
    /// // Modify the data
    /// *lock.lock() = 2;
    ///
    /// // Read the data
    /// let answer = *lock.lock();
    /// assert_eq!(answer, 2);
    /// ```
    ///
    /// # Thread safety example
    ///
    /// ```
    /// use spin;
    /// use std::sync::{Arc, Barrier};
    ///
    /// let thread_count = 1000;
    /// let spin_mutex = Arc::new(spin::Mutex::new(0));
    ///
    /// // We use a barrier to ensure the readout happens after all writing
    /// let barrier = Arc::new(Barrier::new(thread_count + 1));
    ///
    /// for _ in (0..thread_count) {
    ///     let my_barrier = barrier.clone();
    ///     let my_lock = spin_mutex.clone();
    ///     std::thread::spawn(move || {
    ///         let mut guard = my_lock.lock();
    ///         *guard += 1;
    ///
    ///         // Release the lock to prevent a deadlock
    ///         drop(guard);
    ///         my_barrier.wait();
    ///     });
    /// }
    ///
    /// barrier.wait();
    ///
    /// let answer = { *spin_mutex.lock() };
    /// assert_eq!(answer, thread_count);
    /// ```
    pub struct Mutex<T: ?Sized> {
        #[cfg(feature = "ticket_mutex")]
        inner: TicketMutex<T>,
        #[cfg(not(feature = "ticket_mutex"))]
        inner: SpinMutex<T>,
    }

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

    /// A generic guard that will protect some data access and
    /// uses either a ticket lock or a normal spin mutex.
    ///
    /// For more info see [`TicketMutexGuard`] or [`SpinMutexGuard`].
    ///
    /// [`TicketMutexGuard`]: ./struct.TicketMutexGuard.html
    /// [`SpinMutexGuard`]: ./struct.SpinMutexGuard.html
    pub struct MutexGuard<'a, T: 'a + ?Sized> {
        #[cfg(feature = "ticket_mutex")]
        inner: TicketMutexGuard<'a, T>,
        #[cfg(not(feature = "ticket_mutex"))]
        inner: SpinMutexGuard<'a, T>,
    }

    impl<T> Mutex<T> {
        /// Creates a new [`Mutex`] wrapping the supplied data.
        ///
        /// # Example
        ///
        /// ```
        /// use spin::Mutex;
        ///
        /// static MUTEX: Mutex<()> = Mutex::new(());
        ///
        /// fn demo() {
        ///     let lock = MUTEX.lock();
        ///     // do something with lock
        ///     drop(lock);
        /// }
        /// ```
        #[inline(always)]
        pub const fn new(value: T) -> Self {
            Self { inner: InnerMutex::new(value) }
        }

        /// Consumes this [`Mutex`] and unwraps the underlying data.
        ///
        /// # Example
        ///
        /// ```
        /// let lock = spin::Mutex::new(42);
        /// assert_eq!(42, lock.into_inner());
        /// ```
        #[inline(always)]
        pub fn into_inner(self) -> T {
            self.inner.into_inner()
        }
    }

    impl<T: ?Sized> Mutex<T> {
        /// Returns `true` if the lock is currently held.
        ///
        /// # Safety
        ///
        /// This function provides no synchronization guarantees and so its result should be considered 'out of date'
        /// the instant it is called. Do not use it for synchronization purposes. However, it may be useful as a heuristic.
        #[inline(always)]
        pub fn is_locked(&self) -> bool {
            self.inner.is_locked()
        }

        /// Locks the [`Mutex`] and returns a guard that permits access to the inner data.
        ///
        /// The returned value may be dereferenced for data access
        /// and the lock will be dropped when the guard falls out of scope.
        ///
        /// ```
        /// let lock = spin::Mutex::new(0);
        /// {
        ///     let mut data = lock.lock();
        ///     // The lock is now locked and the data can be accessed
        ///     *data += 1;
        ///     // The lock is implicitly dropped at the end of the scope
        /// }
        /// ```
        #[inline(always)]
        pub fn lock(&self) -> MutexGuard<T> {
            MutexGuard {
                inner: self.inner.lock(),
            }
        }

        /// Force unlock this [`Mutex`].
        ///
        /// # Safety
        ///
        /// This is *extremely* unsafe if the lock is not held by the current
        /// thread. However, this can be useful in some instances for exposing the
        /// lock to FFI that doesn't know how to deal with RAII.
        #[inline(always)]
        pub unsafe fn force_unlock(&self) {
            self.inner.force_unlock()
        }

        /// Try to lock this [`Mutex`], returning a lock guard if successful.
        ///
        /// # Example
        ///
        /// ```
        /// let lock = spin::Mutex::new(42);
        ///
        /// let maybe_guard = lock.try_lock();
        /// assert!(maybe_guard.is_some());
        ///
        /// // `maybe_guard` is still held, so the second call fails
        /// let maybe_guard2 = lock.try_lock();
        /// assert!(maybe_guard2.is_none());
        /// ```
        #[inline(always)]
        pub fn try_lock(&self) -> Option<MutexGuard<T>> {
            self.inner
                .try_lock()
                .map(|guard| MutexGuard { inner: guard })
        }

        /// Returns a mutable reference to the underlying data.
        ///
        /// Since this call borrows the [`Mutex`] mutably, and a mutable reference is guaranteed to be exclusive in Rust,
        /// no actual locking needs to take place -- the mutable borrow statically guarantees no locks exist. As such,
        /// this is a 'zero-cost' operation.
        ///
        /// # Example
        ///
        /// ```
        /// let mut lock = spin::Mutex::new(0);
        /// *lock.get_mut() = 10;
        /// assert_eq!(*lock.lock(), 10);
        /// ```
        #[inline(always)]
        pub fn get_mut(&mut self) -> &mut T {
            self.inner.get_mut()
        }
    }

    impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Debug::fmt(&self.inner, f)
        }
    }

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

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

    impl<'a, T: ?Sized> MutexGuard<'a, T> {
        /// Leak the lock guard, yielding a mutable reference to the underlying data.
        ///
        /// Note that this function will permanently lock the original [`Mutex`].
        ///
        /// ```
        /// let mylock = spin::Mutex::new(0);
        ///
        /// let data: &mut i32 = spin::MutexGuard::leak(mylock.lock());
        ///
        /// *data = 1;
        /// assert_eq!(*data, 1);
        /// ```
        #[inline(always)]
        pub fn leak(this: Self) -> &'a mut T {
            InnerMutexGuard::leak(this.inner)
        }
    }

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

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

    impl<'a, T: ?Sized> Deref for MutexGuard<'a, T> {
        type Target = T;
        fn deref(&self) -> &T {
            &*self.inner
        }
    }

    impl<'a, T: ?Sized> DerefMut for MutexGuard<'a, T> {
        fn deref_mut(&mut self) -> &mut T {
            &mut *self.inner
        }
    }

    #[cfg(feature = "lock_api1")]
    unsafe impl lock_api::RawMutex for Mutex<()> {
        type GuardMarker = lock_api::GuardSend;

        const INIT: Self = Self::new(());

        fn lock(&self) {
            // Prevent guard destructor running
            core::mem::forget(Self::lock(self));
        }

        fn try_lock(&self) -> bool {
            // Prevent guard destructor running
            Self::try_lock(self).map(core::mem::forget).is_some()
        }

        unsafe fn unlock(&self) {
            self.force_unlock();
        }

        fn is_locked(&self) -> bool {
            self.inner.is_locked()
        }
    }