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Diffstat (limited to 'library/std/src/sys_common/remutex.rs')
| -rw-r--r-- | library/std/src/sys_common/remutex.rs | 178 |
1 files changed, 0 insertions, 178 deletions
diff --git a/library/std/src/sys_common/remutex.rs b/library/std/src/sys_common/remutex.rs deleted file mode 100644 index 4c054da64..000000000 --- a/library/std/src/sys_common/remutex.rs +++ /dev/null @@ -1,178 +0,0 @@ -#[cfg(all(test, not(target_os = "emscripten")))] -mod tests; - -use crate::cell::UnsafeCell; -use crate::ops::Deref; -use crate::panic::{RefUnwindSafe, UnwindSafe}; -use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed}; -use crate::sys::locks as sys; - -/// A re-entrant mutual exclusion -/// -/// This mutex will block *other* threads waiting for the lock to become -/// available. The thread which has already locked the mutex can lock it -/// multiple times without blocking, preventing a common source of deadlocks. -/// -/// This is used by stdout().lock() and friends. -/// -/// ## Implementation details -/// -/// The 'owner' field tracks which thread has locked the mutex. -/// -/// We use current_thread_unique_ptr() as the thread identifier, -/// which is just the address of a thread local variable. -/// -/// If `owner` is set to the identifier of the current thread, -/// we assume the mutex is already locked and instead of locking it again, -/// we increment `lock_count`. -/// -/// When unlocking, we decrement `lock_count`, and only unlock the mutex when -/// it reaches zero. -/// -/// `lock_count` is protected by the mutex and only accessed by the thread that has -/// locked the mutex, so needs no synchronization. -/// -/// `owner` can be checked by other threads that want to see if they already -/// hold the lock, so needs to be atomic. If it compares equal, we're on the -/// same thread that holds the mutex and memory access can use relaxed ordering -/// since we're not dealing with multiple threads. If it compares unequal, -/// synchronization is left to the mutex, making relaxed memory ordering for -/// the `owner` field fine in all cases. -pub struct ReentrantMutex<T> { - mutex: sys::Mutex, - owner: AtomicUsize, - lock_count: UnsafeCell<u32>, - data: T, -} - -unsafe impl<T: Send> Send for ReentrantMutex<T> {} -unsafe impl<T: Send> Sync for ReentrantMutex<T> {} - -impl<T> UnwindSafe for ReentrantMutex<T> {} -impl<T> RefUnwindSafe for ReentrantMutex<T> {} - -/// 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 implementation. -/// -/// # Mutability -/// -/// Unlike `MutexGuard`, `ReentrantMutexGuard` does not implement `DerefMut`, -/// because implementation of the trait would violate Rust’s reference aliasing -/// rules. Use interior mutability (usually `RefCell`) in order to mutate the -/// guarded data. -#[must_use = "if unused the ReentrantMutex will immediately unlock"] -pub struct ReentrantMutexGuard<'a, T: 'a> { - lock: &'a ReentrantMutex<T>, -} - -impl<T> !Send for ReentrantMutexGuard<'_, T> {} - -impl<T> ReentrantMutex<T> { - /// Creates a new reentrant mutex in an unlocked state. - pub const fn new(t: T) -> ReentrantMutex<T> { - ReentrantMutex { - mutex: sys::Mutex::new(), - owner: AtomicUsize::new(0), - lock_count: UnsafeCell::new(0), - data: t, - } - } - - /// Acquires a mutex, blocking the current thread until it is able to do so. - /// - /// This function will block the caller until it is available to acquire the mutex. - /// Upon returning, the thread is the only thread with the mutex held. When the thread - /// calling this method already holds the lock, the call shall succeed without - /// blocking. - /// - /// # Errors - /// - /// If another user of this mutex panicked while holding the mutex, then - /// this call will return failure if the mutex would otherwise be - /// acquired. - pub fn lock(&self) -> ReentrantMutexGuard<'_, T> { - let this_thread = current_thread_unique_ptr(); - // Safety: We only touch lock_count when we own the lock. - unsafe { - if self.owner.load(Relaxed) == this_thread { - self.increment_lock_count(); - } else { - self.mutex.lock(); - self.owner.store(this_thread, Relaxed); - debug_assert_eq!(*self.lock_count.get(), 0); - *self.lock_count.get() = 1; - } - } - ReentrantMutexGuard { lock: self } - } - - /// Attempts to acquire this lock. - /// - /// If the lock could not be acquired at this time, then `Err` is returned. - /// Otherwise, an RAII guard is returned. - /// - /// This function does not block. - /// - /// # Errors - /// - /// If another user of this mutex panicked while holding the mutex, then - /// this call will return failure if the mutex would otherwise be - /// acquired. - pub fn try_lock(&self) -> Option<ReentrantMutexGuard<'_, T>> { - let this_thread = current_thread_unique_ptr(); - // Safety: We only touch lock_count when we own the lock. - unsafe { - if self.owner.load(Relaxed) == this_thread { - self.increment_lock_count(); - Some(ReentrantMutexGuard { lock: self }) - } else if self.mutex.try_lock() { - self.owner.store(this_thread, Relaxed); - debug_assert_eq!(*self.lock_count.get(), 0); - *self.lock_count.get() = 1; - Some(ReentrantMutexGuard { lock: self }) - } else { - None - } - } - } - - unsafe fn increment_lock_count(&self) { - *self.lock_count.get() = (*self.lock_count.get()) - .checked_add(1) - .expect("lock count overflow in reentrant mutex"); - } -} - -impl<T> Deref for ReentrantMutexGuard<'_, T> { - type Target = T; - - fn deref(&self) -> &T { - &self.lock.data - } -} - -impl<T> Drop for ReentrantMutexGuard<'_, T> { - #[inline] - fn drop(&mut self) { - // Safety: We own the lock. - unsafe { - *self.lock.lock_count.get() -= 1; - if *self.lock.lock_count.get() == 0 { - self.lock.owner.store(0, Relaxed); - self.lock.mutex.unlock(); - } - } - } -} - -/// Get an address that is unique per running thread. -/// -/// This can be used as a non-null usize-sized ID. -pub fn current_thread_unique_ptr() -> usize { - // Use a non-drop type to make sure it's still available during thread destruction. - thread_local! { static X: u8 = const { 0 } } - X.with(|x| <*const _>::addr(x)) -} |