commit 63ea1029b8fd4e67776acdfc325dbf8138dbedf7 Author: Aleksey Kladov Date: Thu Aug 2 03:11:32 2018 +0300 Initial diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..6936990 --- /dev/null +++ b/.gitignore @@ -0,0 +1,3 @@ +/target +**/*.rs.bk +Cargo.lock diff --git a/.travis.yml b/.travis.yml new file mode 100644 index 0000000..5109310 --- /dev/null +++ b/.travis.yml @@ -0,0 +1,8 @@ +language: rust + +matrix: + include: + - rust: beta + script: + - cargo test + - cargo test --release diff --git a/Cargo.toml b/Cargo.toml new file mode 100644 index 0000000..dc35c8f --- /dev/null +++ b/Cargo.toml @@ -0,0 +1,10 @@ +[package] +name = "once_cell" +version = "0.0.1" +authors = ["Aleksey Kladov "] +categories = [ "rust-patterns" ] +repository = "https://github.com/matklad/once_cell" +description = """ +Lazy and lazy static values without macros +""" +license = "MIT OR Apache-2.0" diff --git a/LICENSE-APACHE b/LICENSE-APACHE new file mode 100644 index 0000000..16fe87b --- /dev/null +++ b/LICENSE-APACHE @@ -0,0 +1,201 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + +TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + +1. 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IN NO EVENT +SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY +CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION +OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR +IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER +DEALINGS IN THE SOFTWARE. diff --git a/README.md b/README.md new file mode 100644 index 0000000..ac25db3 --- /dev/null +++ b/README.md @@ -0,0 +1,33 @@ +# once_cell + +[![Build Status](https://travis-ci.org/matklad/once_cell.svg?branch=master)](https://travis-ci.org/matklad/once_cell) +[![Crates.io](https://img.shields.io/crates/v/once_cell.svg)](https://crates.io/crates/once_cell) +[![API reference](https://docs.rs/once_cell/badge.svg)](https://docs.rs/once_cell/) + +A macroless alternative to [`lazy_static`](https://github.com/rust-lang-nursery/lazy-static.rs). +If you like this, you might also like [`lazycell`](https://github.com/indiv0/lazycell/) + +```rust +fn hashmap() -> &'static HashMap { + static INSTANCE: OnceCell> = OnceCell::INIT; + INSTANCE.get_or_init(|| { + let mut m = HashMap::new(); + m.insert(0, "foo"); + m.insert(1, "bar"); + m.insert(2, "baz"); + m + }) +} +``` + +If you want slightly sweeter syntax, we have macros as well! + +```rust +static HASHMAP: Lazy> = sync_lazy! { + let mut m = HashMap::new(); + m.insert(0, "foo"); + m.insert(1, "bar"); + m.insert(2, "baz"); + m +}; +``` diff --git a/examples/lazy_static.rs b/examples/lazy_static.rs new file mode 100644 index 0000000..ed53d8a --- /dev/null +++ b/examples/lazy_static.rs @@ -0,0 +1,36 @@ +#[macro_use] +extern crate once_cell; + +use std::collections::HashMap; +use once_cell::sync::{Lazy, OnceCell}; + +static HASHMAP: Lazy> = sync_lazy! { + let mut m = HashMap::new(); + m.insert(0, "foo"); + m.insert(1, "bar"); + m.insert(2, "baz"); + m +}; + +// Same, but completely without macros +fn hashmap() -> &'static HashMap { + static INSTANCE: OnceCell> = OnceCell::INIT; + INSTANCE.get_or_init(|| { + let mut m = HashMap::new(); + m.insert(0, "foo"); + m.insert(1, "bar"); + m.insert(2, "baz"); + m + }) +} + +fn main() { + // First access to `HASHMAP` initializes it + println!("The entry for `0` is \"{}\".", HASHMAP.get(&0).unwrap()); + + // Any further access to `HASHMAP` just returns the computed value + println!("The entry for `1` is \"{}\".", HASHMAP.get(&1).unwrap()); + + println!("\nThe entry for `0` is \"{}\".", hashmap().get(&0).unwrap()); + println!("The entry for `1` is \"{}\".", hashmap().get(&1).unwrap()); +} diff --git a/src/lib.rs b/src/lib.rs new file mode 100644 index 0000000..00ea330 --- /dev/null +++ b/src/lib.rs @@ -0,0 +1,209 @@ +#[macro_use] +pub mod unsync { + use std::{ + ops::Deref, + cell::UnsafeCell, + }; + + #[derive(Debug, Default)] + pub struct OnceCell { + // Invariant: written to at most once. + inner: UnsafeCell>, + } + + impl OnceCell { + pub const INIT: OnceCell = OnceCell { inner: UnsafeCell::new(None) }; + + pub fn new() -> OnceCell { + OnceCell { inner: UnsafeCell::new(None) } + } + + pub fn get(&self) -> Option<&T> { + // Safe due to `inner`'s invariant + unsafe { &*self.inner.get() }.as_ref() + } + + pub fn set(&self, value: T) -> Result<(), T> { + let slot = unsafe { &mut *self.inner.get() }; + if slot.is_some() { + return Err(value); + } + // This is the only place where we set the slot, + // no races due to reentrancy/concurrency are possible, + // and we've checked that slot is currently `None`, so + // this write maintains the `inner`'s invariant. + *slot = Some(value); + Ok(()) + } + + pub fn get_or_init(&self, f: impl FnOnce() -> T) -> &T { + enum Void {} + match self.get_or_try_init(|| Ok::(f())) { + Ok(val) => val, + Err(void) => match void {}, + } + } + + pub fn get_or_try_init(&self, f: impl FnOnce() -> Result) -> Result<&T, E> { + if let Some(val) = self.get() { + return Ok(val); + } + let val = f()?; + assert!(self.set(val).is_ok(), "reentrant init"); + Ok(self.get().unwrap()) + } + } + + #[derive(Debug)] + pub struct Lazy T = fn() -> T> { + #[doc(hidden)] + pub __cell: OnceCell, + #[doc(hidden)] + pub __init: F, + } + + impl T> Lazy { + pub fn new(f: F) -> Lazy { + Lazy { + __cell: OnceCell::INIT, + __init: f, + } + } + } + + impl T> Deref for Lazy { + type Target = T; + fn deref(&self) -> &T { + self.__cell.get_or_init(|| (self.__init)()) + } + } + + #[macro_export] + macro_rules! unsync_lazy { + ($($block:tt)*) => { + $crate::unsync::Lazy { + __cell: $crate::unsync::OnceCell::INIT, + __init: || { $($block)* }, + } + }; + } +} + +#[macro_use] +pub mod sync { + use std::{ + ptr, + sync::{Once, atomic::{AtomicPtr, Ordering::Relaxed}}, + ops::Deref, + }; + + #[derive(Debug)] + pub struct OnceCell { + // Invariant: `inner` is written to only from within `once`. + // Corollary: inner is written at most once. + // Corollary: all reads & writes to inner are fine with `Relaxed` ordering. + // Invariant: if not null, ptr came from `Box::into_raw`. + inner: AtomicPtr, + once: Once, + } + + // Why do we need `T: Send`? + // Thread A creates a `OnceCell` and shares it with + // scoped thread B, which fills the cell, which is + // then destroyed by A. That is, destructor observes + // a sent value. + unsafe impl Sync for OnceCell {} + + unsafe impl Send for OnceCell {} + + impl OnceCell { + pub const INIT: OnceCell = OnceCell { + inner: AtomicPtr::new(ptr::null_mut()), + once: Once::new(), + }; + + pub fn new() -> OnceCell { + OnceCell { + inner: AtomicPtr::new(ptr::null_mut()), + once: Once::new(), + } + } + + pub fn get(&self) -> Option<&T> { + let ptr = self.inner.load(Relaxed); + // Safe due to Corollary + unsafe { ptr.as_ref() } + } + + pub fn set(&self, value: T) -> Result<(), T> { + let mut value = Some(value); + self.once.call_once(|| { + let value = value.take().unwrap(); + unsafe { self.set_inner(value) } + }); + match value { + None => Ok(()), + Some(value) => Err(value) + } + } + + /// Guarantees that only one `f` is ever called. + pub fn get_or_init(&self, f: impl FnOnce() -> T) -> &T { + self.once.call_once(|| { + let value = f(); + unsafe { self.set_inner(value); } + }); + self.get().unwrap() + } + + // Invariant: must be called from `self.once`. + unsafe fn set_inner(&self, value: T) { + let ptr = Box::into_raw(Box::new(value)); + self.inner.store(ptr, Relaxed); + } + } + + impl Drop for OnceCell { + fn drop(&mut self) { + let ptr = self.inner.load(Relaxed); + // Safe due to Corollary + unsafe { + drop(Box::from_raw(ptr)) + } + } + } + + #[derive(Debug)] + pub struct Lazy T = fn() -> T> { + #[doc(hidden)] + pub __cell: OnceCell, + #[doc(hidden)] + pub __init: F, + } + + impl T> Lazy { + pub fn new(f: F) -> Lazy { + Lazy { + __cell: OnceCell::new(), + __init: f, + } + } + } + + impl T> Deref for Lazy { + type Target = T; + fn deref(&self) -> &T { + self.__cell.get_or_init(|| (self.__init)()) + } + } + + #[macro_export] + macro_rules! sync_lazy { + ($($block:tt)*) => { + $crate::sync::Lazy { + __cell: $crate::sync::OnceCell::INIT, + __init: || { $($block)* }, + } + }; + } +} diff --git a/tests/test.rs b/tests/test.rs new file mode 100644 index 0000000..04bdb99 --- /dev/null +++ b/tests/test.rs @@ -0,0 +1,159 @@ +#[macro_use] +extern crate once_cell; + +use std::{ + mem, + thread, + ptr, + cell::Cell, + sync::atomic::{AtomicUsize, Ordering::SeqCst}, +}; +use once_cell::{sync, unsync}; + +fn go ()>(mut f: F) { + struct Yolo(T); + unsafe impl Send for Yolo {} + + let ptr: *const u8 = &mut f as *const F as *const u8; + mem::forget(f); + let yolo = Yolo(ptr); + thread::spawn(move || { + let f: F = unsafe { ptr::read(yolo.0 as *const F) }; + f(); + }).join().unwrap(); +} + +#[test] +fn unsync_once_cell() { + let c = unsync::OnceCell::new(); + assert!(c.get().is_none()); + c.get_or_init(|| 92); + assert_eq!(c.get(), Some(&92)); + + c.get_or_init(|| { + panic!("Kabom!") + }); + assert_eq!(c.get(), Some(&92)); +} + +#[test] +fn sync_once_cell() { + let c = sync::OnceCell::new(); + assert!(c.get().is_none()); + go(|| { + c.get_or_init(|| 92); + assert_eq!(c.get(), Some(&92)); + }); + c.get_or_init(|| panic!("Kabom!")); + assert_eq!(c.get(), Some(&92)); +} + +#[test] +fn unsync_once_cell_drop() { + static DROP_CNT: AtomicUsize = AtomicUsize::new(0); + struct Dropper; + impl Drop for Dropper { + fn drop(&mut self) { + DROP_CNT.fetch_add(1, SeqCst); + } + } + + let x = unsync::OnceCell::new(); + x.get_or_init(|| Dropper); + assert_eq!(DROP_CNT.load(SeqCst), 0); + drop(x); + assert_eq!(DROP_CNT.load(SeqCst), 1); +} + +#[test] +fn sync_once_cell_drop() { + static DROP_CNT: AtomicUsize = AtomicUsize::new(0); + struct Dropper; + impl Drop for Dropper { + fn drop(&mut self) { + DROP_CNT.fetch_add(1, SeqCst); + } + } + + let x = sync::OnceCell::new(); + go(|| { + x.get_or_init(|| Dropper); + assert_eq!(DROP_CNT.load(SeqCst), 0); + drop(x); + }); + assert_eq!(DROP_CNT.load(SeqCst), 1); +} + +#[test] +fn unsync_lazy_macro() { + let called = Cell::new(0); + let x = unsync_lazy! { + called.set(called.get() + 1); + 92 + }; + + assert_eq!(called.get(), 0); + + let y = *x - 30; + assert_eq!(y, 62); + assert_eq!(called.get(), 1); + + let y = *x - 30; + assert_eq!(y, 62); + assert_eq!(called.get(), 1); +} + +#[test] +fn sync_lazy_macro() { + let called = AtomicUsize::new(0); + let x = sync_lazy! { + called.fetch_add(1, SeqCst); + 92 + }; + + assert_eq!(called.load(SeqCst), 0); + + go(|| { + let y = *x - 30; + assert_eq!(y, 62); + assert_eq!(called.load(SeqCst), 1); + }); + + let y = *x - 30; + assert_eq!(y, 62); + assert_eq!(called.load(SeqCst), 1); +} + + +#[test] +fn static_lazy() { + static XS: sync::Lazy> = sync_lazy! { + let mut xs = Vec::new(); + xs.push(1); + xs.push(2); + xs.push(3); + xs + }; + assert_eq!(&*XS, &vec![1, 2, 3]); +} + +#[test] +fn static_lazy_no_macros() { + fn xs() -> &'static Vec { + static XS: sync::OnceCell> = sync::OnceCell::INIT; + XS.get_or_init(|| { + let mut xs = Vec::new(); + xs.push(1); + xs.push(2); + xs.push(3); + xs + }) + } + assert_eq!(xs(), &vec![1, 2, 3]); +} + +#[test] +fn sync_once_cell_is_sync_send() { + fn assert_traits() {} + assert_traits::>(); +}