use std::fmt::Debug;
use lock_api::RawRwLock;
use crate::lockable::{Lockable, RawLock};
use crate::ThreadKey;
use super::{RwLock, RwLockWriteGuard, RwLockWriteRef, WriteLock};
unsafe impl<T: Send, R: RawRwLock + Send + Sync> Lockable for WriteLock<'_, T, R> {
type Guard<'g>
= RwLockWriteRef<'g, T, R>
where
Self: 'g;
type DataMut<'a>
= &'a mut T
where
Self: 'a;
fn get_ptrs<'a>(&'a self, ptrs: &mut Vec<&'a dyn RawLock>) {
ptrs.push(self.as_ref());
}
unsafe fn guard(&self) -> Self::Guard<'_> {
RwLockWriteRef::new(self.as_ref())
}
unsafe fn data_mut(&self) -> Self::DataMut<'_> {
self.0.data_mut()
}
}
// Technically, the exclusive locks can also be shared, but there's currently
// no way to express that. I don't think I want to ever express that.
#[mutants::skip]
#[cfg(not(tarpaulin_include))]
impl<T: ?Sized + Debug, R: RawRwLock> Debug for WriteLock<'_, T, R> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
// safety: this is just a try lock, and the value is dropped
// immediately after, so there's no risk of blocking ourselves
// or any other threads
// It makes zero sense to try using an exclusive lock for this, so this
// is the only time when WriteLock does a read.
if let Some(value) = unsafe { self.0.try_read_no_key() } {
f.debug_struct("WriteLock").field("data", &&*value).finish()
} else {
struct LockedPlaceholder;
impl Debug for LockedPlaceholder {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str("<locked>")
}
}
f.debug_struct("WriteLock")
.field("data", &LockedPlaceholder)
.finish()
}
}
}
impl<'l, T, R> From<&'l RwLock<T, R>> for WriteLock<'l, T, R> {
fn from(value: &'l RwLock<T, R>) -> Self {
Self::new(value)
}
}
impl<T: ?Sized, R> AsRef<RwLock<T, R>> for WriteLock<'_, T, R> {
fn as_ref(&self) -> &RwLock<T, R> {
self.0
}
}
impl<'l, T, R> WriteLock<'l, T, R> {
/// Creates a new `WriteLock` which accesses the given [`RwLock`]
///
/// # Examples
///
/// ```
/// use happylock::{rwlock::WriteLock, RwLock};
///
/// let lock = RwLock::new(5);
/// let write_lock = WriteLock::new(&lock);
/// ```
#[must_use]
pub const fn new(rwlock: &'l RwLock<T, R>) -> Self {
Self(rwlock)
}
}
impl<T: ?Sized, R: RawRwLock> WriteLock<'_, T, R> {
/// Locks the underlying [`RwLock`] with exclusive write access, blocking
/// the current until it can be acquired.
///
/// This function will not return while other writers or readers currently
/// have access to the lock.
///
/// Returns an RAII guard which will drop the write access of this `RwLock`
/// when dropped.
///
/// Because this method takes a [`ThreadKey`], it's not possible for this
/// method to cause a deadlock.
///
/// # Examples
///
/// ```
/// use happylock::{ThreadKey, RwLock};
/// use happylock::rwlock::WriteLock;
///
/// let key = ThreadKey::get().unwrap();
/// let lock = RwLock::new(1);
/// let writer = WriteLock::new(&lock);
///
/// let mut n = writer.lock(key);
/// *n += 2;
/// ```
///
/// [`ThreadKey`]: `crate::ThreadKey`
#[must_use]
pub fn lock(&self, key: ThreadKey) -> RwLockWriteGuard<'_, T, R> {
self.0.write(key)
}
/// Attempts to lock the underlying [`RwLock`] with exclusive write access.
///
/// This function does not block. If the lock could not be acquired at this
/// time, then `None` is returned. Otherwise, an RAII guard is returned
/// which will release the lock when it is dropped.
///
/// This function does not provide any guarantees with respect to the
/// ordering of whether contentious readers or writers will acquire the
/// lock first.
///
/// # Errors
///
/// If the [`RwLock`] could not be acquired because it was already locked,
/// then an error will be returned containing the given key.
///
/// # Examples
///
/// ```
/// use happylock::{RwLock, ThreadKey};
/// use happylock::rwlock::WriteLock;
///
/// let key = ThreadKey::get().unwrap();
/// let lock = RwLock::new(1);
/// let writer = WriteLock::new(&lock);
///
/// match writer.try_lock(key) {
/// Ok(n) => assert_eq!(*n, 1),
/// Err(_) => unreachable!(),
/// };
/// ```
pub fn try_lock(&self, key: ThreadKey) -> Result<RwLockWriteGuard<'_, T, R>, ThreadKey> {
self.0.try_write(key)
}
// There's no `try_lock_no_key`. Instead, `try_read_no_key` is called on
// the referenced `RwLock`.
/// Immediately drops the guard, and consequently releases the exclusive
/// lock on the underlying [`RwLock`].
///
/// This function is equivalent to calling [`drop`] on the guard, except
/// that it returns the key that was used to create it. Alternately, the
/// guard will be automatically dropped when it goes out of scope.
///
/// # Examples
///
/// ```
/// use happylock::{RwLock, ThreadKey};
/// use happylock::rwlock::WriteLock;
///
/// let key = ThreadKey::get().unwrap();
/// let lock = RwLock::new(0);
/// let writer = WriteLock::new(&lock);
///
/// let mut guard = writer.lock(key);
/// *guard += 20;
/// let key = WriteLock::unlock(guard);
/// ```
#[must_use]
pub fn unlock(guard: RwLockWriteGuard<'_, T, R>) -> ThreadKey {
RwLock::unlock_write(guard)
}
}
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