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//!Semaphore primitive for Rust //! //!## Types //! //!Library supplied two types of semaphores, which generally should not be mixed together as it //!created a mess. //! //!#### Binary //! //!Binary semaphore is similar to the `Mutex` as it allows singular lock & unlock. //! //!This is the approach that should work for most simple use cases. //! //!This implementation is available for all targets. //! //!```rust //! use semka::{Sem, BinarySemaphore}; //! let sem = Sem::new().unwrap(); //! //! let _guard = sem.lock(); //! //!``` //! //!#### Counting Semaphore //! //!Semaphore state is expressed as atomic integer, which gets decremented(if possible) on `wait` //!If decrement is not possible (i.e. state is 0) then it awaits for state to get incremented. //! //!Meanwhile `signal` increments the counter. If any other tried is locked in `wait`, then it also //!wakes one of the locked threads. //! //!```rust //! use semka::{Sem, CountingSemaphore}; //! let sem = Sem::new(0).unwrap(); //! //! assert!(sem.try_lock().is_none()); //! sem.signal(); //! sem.signal(); //! let _guard = sem.lock(); //! assert!(sem.try_wait()); //! assert!(!sem.try_wait()); //! //! drop(_guard); //! assert!(sem.try_wait()); //!``` //! //!## Platform implementation //! //!#### Windows //! //!Uses winapi `CreateSemaphoreW`. //! //!Implements `CountingSemaphore` interface //! //!#### POSIX //! //!All POSIX-compliant systems uses `sem_init` //!But it must be noted that awaiting can be interrupted by the signal //! //!POSIX implementation relies on [libc](https://github.com/rust-lang/libc) //! //!This includes all `unix` targets and `fuchsia` //! //!Implements `CountingSemaphore` interface //! //!### Mac //! //!Uses `mach` API. //! //!Implements `CountingSemaphore` interface //! //!### No OS atomic //! //!Trivial atomic implementation that performs spin loop #[cfg(any(all(unix, not(any(target_os = "macos", target_os = "ios"))), target_os = "fuchsia"))] mod posix; #[cfg(any(all(unix, not(any(target_os = "macos", target_os = "ios"))), target_os = "fuchsia"))] pub use posix::Sem; #[cfg(windows)] mod win32; #[cfg(windows)] pub use win32::Sem; #[cfg(any(target_os = "macos", target_os = "ios"))] mod mac; #[cfg(any(target_os = "macos", target_os = "ios"))] pub use mac::Sem; mod atomic; pub use atomic::Sem as AtomicSem; #[cfg(target_os = "unknown")] pub use atomic::Sem; ///Describes binary Semaphore interface. /// ///It's state can be described as `bool`. ///Any attempt to `wait` would result in locking `self` (i.e. setting state to `true`) ///Which means unless `lock` is dropped, any further `lock` would block calling thread. /// ///Any `CountingSemaphore` can be used as `BinarySemaphore` whenever it's initial count is `1` pub trait BinarySemaphore: Sized { ///Creates new instance, initially unlocked fn new() -> Option<Self>; ///Locks self, returning guard that unlocks on drop. fn lock(&self) -> BinaryLock<'_, Self>; } impl<T: CountingSemaphore> BinarySemaphore for T { #[inline(always)] fn new() -> Option<Self> { T::new(1) } #[inline(always)] fn lock(&self) -> BinaryLock<'_, Self> { T::wait(self); BinaryLock::new(self, T::signal) } } pub struct BinaryLock<'a, T: BinarySemaphore> { sem: &'a T, unlock: fn(&'a T), } impl<'a, T: BinarySemaphore> BinaryLock<'a, T> { #[inline(always)] ///Creates new instance providing reference to semaphore and `fn` to perform unlock pub fn new(sem: &'a T, unlock: fn(&'a T)) -> Self { Self { sem, unlock, } } } impl<T: BinarySemaphore> Drop for BinaryLock<'_, T> { fn drop(&mut self) { (self.unlock)(self.sem) } } ///Describes counting Semaphore interface /// ///This primitive provides access to single integer that can be decremented using signal ///and incremented using wait pub trait CountingSemaphore: Sized { ///Creates new instance, returning None on inability to do so. /// ///`init` is initial value for the semaphore fn new(init: u32) -> Option<Self>; ///Decrements self, returning immediately if it was signaled. /// ///Otherwise awaits for `signal` fn wait(&self); ///Attempts to decrement self, returning whether self was signaled or not. /// ///Returns `true` if self was signaled /// ///Returns `false` otherwise fn try_wait(&self) -> bool; ///Attempts to decrement self within provided time, returning whether self was signaled or not. /// ///Returns `true` if self was signaled within specified `timeout` /// ///Returns `false` otherwise fn wait_timeout(&self, timeout: core::time::Duration) -> bool; ///Increments self, waking any awaiting thread as result fn signal(&self); ///Gets semaphore's guard, which signal on drop. /// ///Before guard is created, function will await for semaphore to get decremented. fn lock(&self) -> SemaphoreGuard<'_, Self> { self.wait(); SemaphoreGuard { sem: self } } ///Attempts to acquire semaphore's guard, which signal on drop. /// ///If semaphore cannot be decremented at the current moment, returns `None` fn try_lock(&self) -> Option<SemaphoreGuard<'_, Self>> { match self.try_wait() { true => Some(SemaphoreGuard { sem: self, }), false => None, } } } ///Semaphore's guard. /// ///Increments(signal) semaphore on drop. pub struct SemaphoreGuard<'a, T: CountingSemaphore> { sem: &'a T, } impl<T: CountingSemaphore> Drop for SemaphoreGuard<'_, T> { fn drop(&mut self) { self.sem.signal(); } }