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use std::sync::Arc;
use tokio::sync::OwnedSemaphorePermit as OwnedSemaphoreBasePermit;
use tokio::sync::Semaphore as SemaphoreBase;
use tokio::sync::SemaphorePermit as SemaphoreBasePermit;
/// Represents a permit to a [Semaphore].
pub struct SemaphorePermit<'a> {
_permit: SemaphoreBasePermit<'a>,
}
/// Represents an owned permit to a [OwnedSemaphore].
pub struct OwnedSemaphorePermit {
_permit: OwnedSemaphoreBasePermit,
}
/// Error when there are no permits available.
#[derive(Debug)]
pub struct NoPermits;
/// A semaphore maintains a set of permits. Permits are used to synchronize access to a shared resource.
/// A semaphore differs from a mutex in that it can allow more than one concurrent caller to access the shared resource at a time.
#[repr(transparent)]
pub struct Semaphore {
inner: SemaphoreBase,
}
/// An owned semaphore is identical to a [Semaphore] except it can be owned by an actor and it's permits can still be shared externally.
#[repr(transparent)]
pub struct OwnedSemaphore {
inner: Arc<SemaphoreBase>,
}
impl Semaphore {
/// Creates a new instance of [Semaphore] with the given `permits` count.
///
/// This is typically used to create a static semaphore:
/// ```
/// use hydra::Semaphore;
///
/// static RATE_LIMIT: Semaphore = Semaphore::new(100);
/// ```
pub const fn new(permits: usize) -> Self {
Self {
inner: SemaphoreBase::const_new(permits),
}
}
/// Acquires one permit asynchronously waiting for one to become available.
#[must_use]
pub async fn acquire(&self) -> SemaphorePermit<'_> {
let permit = self.inner.acquire().await.unwrap();
SemaphorePermit { _permit: permit }
}
/// Acquires many permits asynchronously waiting for them to become available.
#[must_use]
pub async fn acquire_many(&self, count: u32) -> SemaphorePermit<'_> {
let permit = self.inner.acquire_many(count).await.unwrap();
SemaphorePermit { _permit: permit }
}
/// Attempts to acquire a permit, returning an error if there are none available.
pub fn try_acquire(&self) -> Result<SemaphorePermit<'_>, NoPermits> {
let permit = self.inner.try_acquire().map_err(|_| NoPermits)?;
Ok(SemaphorePermit { _permit: permit })
}
}
impl OwnedSemaphore {
/// Creates a new instance of [OwnedSemaphore] with the given `permits` count that can be used with owned permits.
///
/// This can be used to create a owned semaphore that lives in a state:
/// ```
/// use hydra::OwnedSemaphore;
///
/// struct MyServer {
/// rate_limit: OwnedSemaphore,
/// }
///
/// impl MyServer {
/// pub fn new() -> Self {
/// Self {
/// rate_limit: OwnedSemaphore::new(100),
/// }
/// }
/// }
/// ```
pub fn new(permits: usize) -> Self {
Self {
inner: Arc::new(SemaphoreBase::new(permits)),
}
}
/// Acquires one permit asynchronously waiting for one to become available.
#[must_use]
pub async fn acquire(&self) -> SemaphorePermit<'_> {
let permit = self.inner.acquire().await.unwrap();
SemaphorePermit { _permit: permit }
}
/// Acquires one permit asynchronously waiting for one to become available.
#[must_use]
pub async fn acquire_owned(&self) -> OwnedSemaphorePermit {
let permit = self.inner.clone().acquire_owned().await.unwrap();
OwnedSemaphorePermit { _permit: permit }
}
/// Acquires many permits asynchronously waiting for them to become available.
#[must_use]
pub async fn acquire_many(&self, count: u32) -> SemaphorePermit<'_> {
let permit = self.inner.acquire_many(count).await.unwrap();
SemaphorePermit { _permit: permit }
}
/// Acquires many permits asynchronously waiting for them to become available.
#[must_use]
pub async fn acquire_many_owned(&self, count: u32) -> OwnedSemaphorePermit {
let permit = self.inner.clone().acquire_many_owned(count).await.unwrap();
OwnedSemaphorePermit { _permit: permit }
}
/// Attempts to acquire a permit, returning an error if there are none available.
pub fn try_acquire(&self) -> Result<SemaphorePermit<'_>, NoPermits> {
let permit = self.inner.try_acquire().map_err(|_| NoPermits)?;
Ok(SemaphorePermit { _permit: permit })
}
/// Attempts to acquire a permit, returning an error if there are none available.
pub fn try_acquire_owned(&self) -> Result<OwnedSemaphorePermit, NoPermits> {
let permit = self
.inner
.clone()
.try_acquire_owned()
.map_err(|_| NoPermits)?;
Ok(OwnedSemaphorePermit { _permit: permit })
}
}