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//! [![github]](https://github.com/dtolnay/threadbound) [![crates-io]](https://crates.io/crates/threadbound) [![docs-rs]](https://docs.rs/threadbound)
//!
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
//!
//! <br>
//!
//! [`ThreadBound<T>`] is a wrapper that binds a value to its original thread.
//! The wrapper gets to be [`Sync`] and [`Send`] but only the original thread on
//! which the ThreadBound was constructed can retrieve the underlying value.
//!
//! [`ThreadBound<T>`]: struct.ThreadBound.html
//! [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html
//! [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html
//!
//! # Example
//!
//! ```
//! use std::marker::PhantomData;
//! use std::rc::Rc;
//! use std::sync::Arc;
//! use threadbound::ThreadBound;
//!
//! // Neither Send nor Sync. Maybe the index points into a
//! // thread-local interner.
//! #[derive(Copy, Clone)]
//! struct Span {
//! index: u32,
//! marker: PhantomData<Rc<()>>,
//! }
//!
//! // Error types are always supposed to be Send and Sync.
//! // We can use ThreadBound to make it so.
//! struct Error {
//! span: ThreadBound<Span>,
//! message: String,
//! }
//!
//! fn main() {
//! let err = Error {
//! span: ThreadBound::new(Span {
//! index: 99,
//! marker: PhantomData,
//! }),
//! message: "fearless concurrency".to_owned(),
//! };
//!
//! // Original thread can see the contents.
//! assert_eq!(err.span.get_ref().unwrap().index, 99);
//!
//! let err = Arc::new(err);
//! let err2 = err.clone();
//! std::thread::spawn(move || {
//! // Other threads cannot get access. Maybe they use
//! // a default value or a different codepath.
//! assert!(err2.span.get_ref().is_none());
//! });
//!
//! // Original thread can still see the contents.
//! assert_eq!(err.span.get_ref().unwrap().index, 99);
//! }
//! ```
#![doc(html_root_url = "https://docs.rs/threadbound/0.1.5")]
#![allow(clippy::doc_markdown)]
use std::fmt::{self, Debug};
use std::thread::{self, ThreadId};
/// ThreadBound is a Sync-maker and Send-maker that allows accessing a value
/// of type T only from the original thread on which the ThreadBound was
/// constructed.
///
/// Refer to the [crate-level documentation] for a usage example.
///
/// [crate-level documentation]: index.html
pub struct ThreadBound<T> {
value: T,
thread_id: ThreadId,
}
unsafe impl<T> Sync for ThreadBound<T> {}
// Send bound requires Copy, as otherwise Drop could run in the wrong place.
unsafe impl<T: Copy> Send for ThreadBound<T> {}
impl<T> ThreadBound<T> {
/// Binds a value to the current thread. The wrapper can be sent around to
/// other threads, but no other threads will be able to access the
/// underlying value.
pub fn new(value: T) -> Self {
ThreadBound {
value,
thread_id: thread::current().id(),
}
}
/// Accesses a reference to the underlying value if this is its original
/// thread, otherwise `None`.
pub fn get_ref(&self) -> Option<&T> {
if thread::current().id() == self.thread_id {
Some(&self.value)
} else {
None
}
}
/// Accesses a mutable reference to the underlying value if this is its
/// original thread, otherwise `None`.
pub fn get_mut(&mut self) -> Option<&mut T> {
if thread::current().id() == self.thread_id {
Some(&mut self.value)
} else {
None
}
}
/// Extracts ownership of the underlying value if this is its original
/// thread, otherwise `None`.
pub fn into_inner(self) -> Option<T> {
if thread::current().id() == self.thread_id {
Some(self.value)
} else {
None
}
}
}
impl<T: Default> Default for ThreadBound<T> {
fn default() -> Self {
ThreadBound::new(Default::default())
}
}
impl<T: Debug> Debug for ThreadBound<T> {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
match self.get_ref() {
Some(value) => Debug::fmt(value, formatter),
None => formatter.write_str("unknown"),
}
}
}
|
