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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /library/std/src/sync/lazy_lock.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'library/std/src/sync/lazy_lock.rs')
-rw-r--r-- | library/std/src/sync/lazy_lock.rs | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/library/std/src/sync/lazy_lock.rs b/library/std/src/sync/lazy_lock.rs new file mode 100644 index 000000000..535cc1c42 --- /dev/null +++ b/library/std/src/sync/lazy_lock.rs @@ -0,0 +1,121 @@ +use crate::cell::Cell; +use crate::fmt; +use crate::ops::Deref; +use crate::panic::{RefUnwindSafe, UnwindSafe}; +use crate::sync::OnceLock; + +/// A value which is initialized on the first access. +/// +/// This type is a thread-safe `Lazy`, and can be used in statics. +/// +/// # Examples +/// +/// ``` +/// #![feature(once_cell)] +/// +/// use std::collections::HashMap; +/// +/// use std::sync::LazyLock; +/// +/// static HASHMAP: LazyLock<HashMap<i32, String>> = LazyLock::new(|| { +/// println!("initializing"); +/// let mut m = HashMap::new(); +/// m.insert(13, "Spica".to_string()); +/// m.insert(74, "Hoyten".to_string()); +/// m +/// }); +/// +/// fn main() { +/// println!("ready"); +/// std::thread::spawn(|| { +/// println!("{:?}", HASHMAP.get(&13)); +/// }).join().unwrap(); +/// println!("{:?}", HASHMAP.get(&74)); +/// +/// // Prints: +/// // ready +/// // initializing +/// // Some("Spica") +/// // Some("Hoyten") +/// } +/// ``` +#[unstable(feature = "once_cell", issue = "74465")] +pub struct LazyLock<T, F = fn() -> T> { + cell: OnceLock<T>, + init: Cell<Option<F>>, +} + +impl<T, F> LazyLock<T, F> { + /// Creates a new lazy value with the given initializing + /// function. + #[unstable(feature = "once_cell", issue = "74465")] + pub const fn new(f: F) -> LazyLock<T, F> { + LazyLock { cell: OnceLock::new(), init: Cell::new(Some(f)) } + } +} + +impl<T, F: FnOnce() -> T> LazyLock<T, F> { + /// Forces the evaluation of this lazy value and + /// returns a reference to result. This is equivalent + /// to the `Deref` impl, but is explicit. + /// + /// # Examples + /// + /// ``` + /// #![feature(once_cell)] + /// + /// use std::sync::LazyLock; + /// + /// let lazy = LazyLock::new(|| 92); + /// + /// assert_eq!(LazyLock::force(&lazy), &92); + /// assert_eq!(&*lazy, &92); + /// ``` + #[unstable(feature = "once_cell", issue = "74465")] + pub fn force(this: &LazyLock<T, F>) -> &T { + this.cell.get_or_init(|| match this.init.take() { + Some(f) => f(), + None => panic!("Lazy instance has previously been poisoned"), + }) + } +} + +#[unstable(feature = "once_cell", issue = "74465")] +impl<T, F: FnOnce() -> T> Deref for LazyLock<T, F> { + type Target = T; + fn deref(&self) -> &T { + LazyLock::force(self) + } +} + +#[unstable(feature = "once_cell", issue = "74465")] +impl<T: Default> Default for LazyLock<T> { + /// Creates a new lazy value using `Default` as the initializing function. + fn default() -> LazyLock<T> { + LazyLock::new(T::default) + } +} + +#[unstable(feature = "once_cell", issue = "74465")] +impl<T: fmt::Debug, F> fmt::Debug for LazyLock<T, F> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("Lazy").field("cell", &self.cell).finish_non_exhaustive() + } +} + +// We never create a `&F` from a `&LazyLock<T, F>` so it is fine +// to not impl `Sync` for `F` +// we do create a `&mut Option<F>` in `force`, but this is +// properly synchronized, so it only happens once +// so it also does not contribute to this impl. +#[unstable(feature = "once_cell", issue = "74465")] +unsafe impl<T, F: Send> Sync for LazyLock<T, F> where OnceLock<T>: Sync {} +// auto-derived `Send` impl is OK. + +#[unstable(feature = "once_cell", issue = "74465")] +impl<T, F: UnwindSafe> RefUnwindSafe for LazyLock<T, F> where OnceLock<T>: RefUnwindSafe {} +#[unstable(feature = "once_cell", issue = "74465")] +impl<T, F: UnwindSafe> UnwindSafe for LazyLock<T, F> where OnceLock<T>: UnwindSafe {} + +#[cfg(test)] +mod tests; |