├── .github ├── bors.toml └── workflows │ ├── clippy.yml │ ├── rustfmt.yml │ └── test.yml ├── .gitignore ├── CHANGELOG.md ├── Cargo.toml ├── LICENSE-APACHE ├── LICENSE-MIT ├── README.md └── src └── lib.rs /.github/bors.toml: -------------------------------------------------------------------------------- 1 | block_labels = ["needs-decision"] 2 | delete_merged_branches = true 3 | status = [ 4 | "clippy (1.56)", 5 | "clippy (1.63)", 6 | "rustfmt", 7 | "test (1.56)", 8 | "test (1.63)", 9 | ] -------------------------------------------------------------------------------- /.github/workflows/clippy.yml: -------------------------------------------------------------------------------- 1 | name: Clippy check 2 | 3 | on: 4 | push: 5 | branches: [ staging, trying, master ] 6 | pull_request: 7 | 8 | jobs: 9 | clippy: 10 | runs-on: ubuntu-latest 11 | strategy: 12 | matrix: 13 | include: 14 | - rust: 1.56 15 | - rust: 1.63 16 | steps: 17 | - uses: actions/checkout@v2 18 | - name: Install Rust 19 | uses: actions-rs/toolchain@v1 20 | with: 21 | toolchain: ${{matrix.rust}} 22 | components: clippy 23 | override: true 24 | - name: Clippy check 25 | run: cargo clippy -------------------------------------------------------------------------------- /.github/workflows/rustfmt.yml: -------------------------------------------------------------------------------- 1 | name: Code formatting check 2 | 3 | on: 4 | push: 5 | branches: [ staging, trying, master ] 6 | pull_request: 7 | 8 | jobs: 9 | rustfmt: 10 | runs-on: ubuntu-latest 11 | steps: 12 | - uses: actions/checkout@v2 13 | - name: Check fmt 14 | run: cargo fmt -- --check 15 | -------------------------------------------------------------------------------- /.github/workflows/test.yml: -------------------------------------------------------------------------------- 1 | name: Test 2 | 3 | on: 4 | push: 5 | branches: [ staging, trying, master ] 6 | pull_request: 7 | 8 | jobs: 9 | test: 10 | runs-on: ubuntu-latest 11 | strategy: 12 | matrix: 13 | include: 14 | - rust: 1.56 15 | - rust: 1.63 16 | steps: 17 | - uses: actions/checkout@v2 18 | - name: Install Rust 19 | uses: actions-rs/toolchain@v1 20 | with: 21 | toolchain: ${{matrix.rust}} 22 | components: clippy 23 | override: true 24 | - name: Test 25 | run: cargo test 26 | test-nightly: 27 | runs-on: ubuntu-latest 28 | steps: 29 | - uses: actions/checkout@v2 30 | - name: Install Rust 31 | uses: actions-rs/toolchain@v1 32 | with: 33 | toolchain: nightly 34 | override: true 35 | - name: Test 36 | run: cargo test --features nightly 37 | -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | /target 2 | /Cargo.lock 3 | -------------------------------------------------------------------------------- /CHANGELOG.md: -------------------------------------------------------------------------------- 1 | # Changelog 2 | 3 | All notable changes to this project will be documented in this file. 4 | 5 | The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), 6 | and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html). 7 | 8 | ## 2.1.0 - 2024-04-26 9 | 10 | - Added `ConstStaticCell` (#14) 11 | 12 | ## 2.0.0 - 2023-11-02 13 | 14 | - Do not enable feature `critical-section` in `portable-atomic`. In targets that need 15 | atomic polyfilling, you now need to explicitly enable either of `critical-section` or 16 | `unsafe-assume-single-core` in `portable-atomic`. 17 | 18 | ## 1.3.0 - 2023-11-02 19 | 20 | - Switch from `atomic-polyfill` to `portable-atomic`. Note: to be backwards compatible 21 | this crate is enabling the `critical-section` feature in `portable-atomic`. If your 22 | chip is single-core, you might want to upgrade to `static-cell` v2.0 so you can enable 23 | the feature `unsafe-assume-single-core` instead, which is slightly more efficient. 24 | 25 | ## 1.2.0 - 2023-07-03 26 | 27 | - Add panic-free `try_init()`, `try_init_with()`, `try_uninit()`. 28 | 29 | ## 1.1.0 - 2023-06-01 30 | 31 | - Add `uninit()`. 32 | - Add `make_static!` macro. 33 | 34 | ## 1.0.0 - 2022-08-22 35 | 36 | - First release 37 | -------------------------------------------------------------------------------- /Cargo.toml: -------------------------------------------------------------------------------- 1 | [package] 2 | name = "static_cell" 3 | version = "2.1.0" 4 | edition = "2021" 5 | description = "Statically allocated, initialized at runtime cell." 6 | license = "MIT OR Apache-2.0" 7 | repository = "https://github.com/embassy-rs/static-cell" 8 | 9 | [dependencies] 10 | portable-atomic = { version = "1.5.1" } 11 | 12 | [features] 13 | nightly = [] 14 | 15 | [package.metadata.docs.rs] 16 | features = ["nightly"] 17 | rustdoc-args = ["--cfg", "docsrs"] 18 | -------------------------------------------------------------------------------- /LICENSE-APACHE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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IN NO EVENT 21 | SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 22 | CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION 23 | OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR 24 | IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 25 | DEALINGS IN THE SOFTWARE. 26 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # static-cell 2 | [![crates.io](https://img.shields.io/crates/d/static_cell.svg)](https://crates.io/crates/static_cell) 3 | [![crates.io](https://img.shields.io/crates/v/static_cell.svg)](https://crates.io/crates/static_cell) 4 | [![Documentation](https://docs.rs/static_cell/badge.svg)](https://docs.rs/static_cell) 5 | 6 | Statically allocated, initialized at runtime cell. 7 | 8 | `StaticCell` provides a no-std-compatible, no-alloc way to reserve memory at compile time for 9 | a value, but initialize it at runtime, and get a `'static` reference to it. 10 | 11 | This is useful in the following scenarios: 12 | 13 | - You need `&'static T`, but `T` can't be constructed in const context so you can't simply use a `static`. 14 | - You need `&'static mut T`, not just `&'static T`. 15 | 16 | ## Example 17 | 18 | ```rust 19 | use static_cell::StaticCell; 20 | 21 | // Statically allocate memory for a `u32`. 22 | static SOME_INT: StaticCell = StaticCell::new(); 23 | 24 | // Initialize it at runtime. This returns a `&'static mut`. 25 | let x: &'static mut u32 = SOME_INT.init(42); 26 | assert_eq!(*x, 42); 27 | 28 | // Trying to call `.init()` again would panic, because the StaticCell is already initialized. 29 | // SOME_INT.init(42); 30 | ``` 31 | 32 | ## Alternatives 33 | 34 | - If you can use `alloc`, you can use `Box::leak()`. 35 | - If you're OK with `unsafe`, you can use `static mut THING: MaybeUninit`. 36 | - If you need just `&'static T` (instead of `&'static mut T`), there's [`OnceCell`](https://doc.rust-lang.org/stable/core/cell/struct.OnceCell.html) (not thread-safe though) or [`OnceLock`](https://doc.rust-lang.org/stable/std/sync/struct.OnceLock.html) (thread-safe, but requires `std`). 37 | 38 | ## Interoperability 39 | 40 | This crate uses [`portable-atomic`](https://crates.io/crates/portable-atomic), so on targets without native 41 | atomics you must import a crate that provides a [`critical-section`](https://github.com/rust-embedded/critical-section) 42 | implementation. See the `critical-section` README for details. 43 | 44 | ## Minimum Supported Rust Version (MSRV) 45 | 46 | This crate is guaranteed to compile on stable Rust 1.56 and up. It might compile with 47 | older versions but that may change in any new patch release. 48 | 49 | ## License 50 | 51 | This work is licensed under either of 52 | 53 | - Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or 54 | ) 55 | - MIT license ([LICENSE-MIT](LICENSE-MIT) or ) 56 | 57 | at your option. 58 | 59 | ## Contribution 60 | 61 | Unless you explicitly state otherwise, any contribution intentionally submitted 62 | for inclusion in the work by you, as defined in the Apache-2.0 license, shall be 63 | dual licensed as above, without any additional terms or conditions. 64 | -------------------------------------------------------------------------------- /src/lib.rs: -------------------------------------------------------------------------------- 1 | #![cfg_attr(not(test), no_std)] 2 | #![doc = include_str!("../README.md")] 3 | #![cfg_attr(docsrs, feature(doc_cfg))] 4 | #![cfg_attr(feature = "nightly", feature(type_alias_impl_trait))] // for tests 5 | 6 | use core::cell::UnsafeCell; 7 | use core::mem::MaybeUninit; 8 | 9 | use portable_atomic::{AtomicBool, Ordering}; 10 | 11 | /// Statically allocated, initialized at runtime cell. 12 | /// 13 | /// It has two states: "empty" and "full". It is created "empty", and obtaining a reference 14 | /// to the contents permanently changes it to "full". This allows that reference to be valid 15 | /// forever. 16 | /// 17 | /// If your value can be initialized as a `const` value, consider using [`ConstStaticCell`] 18 | /// instead if you only need to take the value at runtime. 19 | /// 20 | /// See the [crate-level docs](crate) for usage. 21 | pub struct StaticCell { 22 | used: AtomicBool, 23 | val: UnsafeCell>, 24 | } 25 | 26 | unsafe impl Send for StaticCell {} 27 | unsafe impl Sync for StaticCell {} 28 | 29 | impl StaticCell { 30 | /// Create a new, empty `StaticCell`. 31 | /// 32 | /// It can be initialized at runtime with [`StaticCell::init()`] or similar methods. 33 | #[inline] 34 | pub const fn new() -> Self { 35 | Self { 36 | used: AtomicBool::new(false), 37 | val: UnsafeCell::new(MaybeUninit::uninit()), 38 | } 39 | } 40 | 41 | /// Initialize the `StaticCell` with a value, returning a mutable reference to it. 42 | /// 43 | /// Using this method, the compiler usually constructs `val` in the stack and then moves 44 | /// it into the `StaticCell`. If `T` is big, this is likely to cause stack overflows. 45 | /// Considering using [`StaticCell::init_with`] instead, which will construct it in-place inside the `StaticCell`. 46 | /// 47 | /// # Panics 48 | /// 49 | /// Panics if this `StaticCell` is already full. 50 | #[inline] 51 | #[allow(clippy::mut_from_ref)] 52 | pub fn init(&'static self, val: T) -> &'static mut T { 53 | self.uninit().write(val) 54 | } 55 | 56 | /// Initialize the `StaticCell` with the closure's return value, returning a mutable reference to it. 57 | /// 58 | /// The advantage over [`StaticCell::init`] is that this method allows the closure to construct 59 | /// the `T` value in-place directly inside the `StaticCell`, saving stack space. 60 | /// 61 | /// # Panics 62 | /// 63 | /// Panics if this `StaticCell` is already full. 64 | #[inline] 65 | #[allow(clippy::mut_from_ref)] 66 | pub fn init_with(&'static self, val: impl FnOnce() -> T) -> &'static mut T { 67 | self.uninit().write(val()) 68 | } 69 | 70 | /// Return a mutable reference to the uninitialized memory owned by the `StaticCell`. 71 | /// 72 | /// Using this method directly is not recommended, but it can be used to construct `T` in-place directly 73 | /// in a guaranteed fashion. 74 | /// 75 | /// # Panics 76 | /// 77 | /// Panics if this `StaticCell` is already full. 78 | #[inline] 79 | #[allow(clippy::mut_from_ref)] 80 | pub fn uninit(&'static self) -> &'static mut MaybeUninit { 81 | if let Some(val) = self.try_uninit() { 82 | val 83 | } else { 84 | panic!("`StaticCell` is already full, it can't be initialized twice."); 85 | } 86 | } 87 | 88 | /// Try initializing the `StaticCell` with a value, returning a mutable reference to it. 89 | /// 90 | /// If this `StaticCell` is already full, it returns `None`. 91 | /// 92 | /// Using this method, the compiler usually constructs `val` in the stack and then moves 93 | /// it into the `StaticCell`. If `T` is big, this is likely to cause stack overflows. 94 | /// Considering using [`StaticCell::try_init_with`] instead, which will construct it in-place inside the `StaticCell`. 95 | /// 96 | /// Will only return a Some(&'static mut T) when the `StaticCell` was not yet initialized. 97 | #[inline] 98 | #[allow(clippy::mut_from_ref)] 99 | pub fn try_init(&'static self, val: T) -> Option<&'static mut T> { 100 | Some(self.try_uninit()?.write(val)) 101 | } 102 | 103 | /// Try initializing the `StaticCell` with the closure's return value, returning a mutable reference to it. 104 | /// 105 | /// If this `StaticCell` is already full, it returns `None`. 106 | /// 107 | /// The advantage over [`StaticCell::init`] is that this method allows the closure to construct 108 | /// the `T` value in-place directly inside the `StaticCell`, saving stack space. 109 | /// 110 | #[inline] 111 | #[allow(clippy::mut_from_ref)] 112 | pub fn try_init_with(&'static self, val: impl FnOnce() -> T) -> Option<&'static mut T> { 113 | Some(self.try_uninit()?.write(val())) 114 | } 115 | 116 | /// Try returning a mutable reference to the uninitialized memory owned by the `StaticCell`. 117 | /// 118 | /// If this `StaticCell` is already full, it returns `None`. 119 | /// 120 | /// Using this method directly is not recommended, but it can be used to construct `T` in-place directly 121 | /// in a guaranteed fashion. 122 | #[inline] 123 | pub fn try_uninit(&'static self) -> Option<&'static mut MaybeUninit> { 124 | if self 125 | .used 126 | .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed) 127 | .is_ok() 128 | { 129 | // SAFETY: We just checked that the value is not yet taken and marked it as taken. 130 | let val = unsafe { &mut *self.val.get() }; 131 | Some(val) 132 | } else { 133 | None 134 | } 135 | } 136 | } 137 | 138 | // --- 139 | 140 | /// Statically allocated and initialized, taken at runtime cell. 141 | /// 142 | /// It has two states: "untaken" and "taken". It is created "untaken", and obtaining a reference 143 | /// to the contents permanently changes it to "taken". This allows that reference to be valid 144 | /// forever. 145 | /// 146 | /// If your value can be const defined, for example a large, zero filled buffer used for DMA 147 | /// or other scratch memory usage, `ConstStaticCell` can be used to guarantee the initializer 148 | /// will never take up stack memory. 149 | /// 150 | /// If your values are all zero initialized, the resulting `ConstStaticCell` should be placed 151 | /// in `.bss`, not taking flash space for initialization either. 152 | /// 153 | /// See the [crate-level docs](crate) for usage. 154 | pub struct ConstStaticCell { 155 | taken: AtomicBool, 156 | val: UnsafeCell, 157 | } 158 | 159 | unsafe impl Send for ConstStaticCell {} 160 | unsafe impl Sync for ConstStaticCell {} 161 | 162 | impl ConstStaticCell { 163 | /// Create a new, empty `ConstStaticCell`. 164 | /// 165 | /// It can be taken at runtime with [`ConstStaticCell::take()`] or similar methods. 166 | #[inline] 167 | pub const fn new(value: T) -> Self { 168 | Self { 169 | taken: AtomicBool::new(false), 170 | val: UnsafeCell::new(value), 171 | } 172 | } 173 | 174 | /// Take the `ConstStaticCell`, returning a mutable reference to it. 175 | /// 176 | /// # Panics 177 | /// 178 | /// Panics if this `ConstStaticCell` was already taken. 179 | #[inline] 180 | #[allow(clippy::mut_from_ref)] 181 | pub fn take(&'static self) -> &'static mut T { 182 | if let Some(val) = self.try_take() { 183 | val 184 | } else { 185 | panic!("`ConstStaticCell` is already taken, it can't be taken twice") 186 | } 187 | } 188 | 189 | /// Try to take the `ConstStaticCell`, returning None if it was already taken 190 | #[inline] 191 | #[allow(clippy::mut_from_ref)] 192 | pub fn try_take(&'static self) -> Option<&'static mut T> { 193 | if self 194 | .taken 195 | .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed) 196 | .is_ok() 197 | { 198 | // SAFETY: We just checked that the value is not yet taken and marked it as taken. 199 | let val = unsafe { &mut *self.val.get() }; 200 | Some(val) 201 | } else { 202 | None 203 | } 204 | } 205 | } 206 | 207 | /// Convert a `T` to a `&'static mut T`. 208 | /// 209 | /// The macro declares a `static StaticCell` and then initializes it when run, returning the `&'static mut`. 210 | /// Therefore, each instance can only be run once. Next runs will panic. The `static` can additionally be 211 | /// decorated with attributes, such as `#[link_section]`, `#[used]`, et al. 212 | /// 213 | /// This macro is nightly-only. It requires `#![feature(type_alias_impl_trait)]` in the crate using it. 214 | /// 215 | /// # Examples 216 | /// 217 | /// ``` 218 | /// # #![feature(type_alias_impl_trait)] 219 | /// use static_cell::make_static; 220 | /// 221 | /// # fn main() { 222 | /// let x: &'static mut u32 = make_static!(42); 223 | /// 224 | /// // This attribute instructs the linker to allocate it in the external RAM's BSS segment. 225 | /// // This specific example is for ESP32S3 with PSRAM support. 226 | /// let buf = make_static!([0u8; 4096], #[link_section = ".ext_ram.bss.buf"]); 227 | /// 228 | /// // Multiple attributes can be supplied. 229 | /// let s = make_static!(0usize, #[used] #[export_name = "exported_symbol_name"]); 230 | /// # } 231 | /// ``` 232 | #[cfg(feature = "nightly")] 233 | #[cfg_attr(docsrs, doc(cfg(feature = "nightly")))] 234 | #[macro_export] 235 | macro_rules! make_static { 236 | ($val:expr) => ($crate::make_static!($val, )); 237 | ($val:expr, $(#[$m:meta])*) => {{ 238 | type T = impl ::core::marker::Sized; 239 | $(#[$m])* 240 | static STATIC_CELL: $crate::StaticCell = $crate::StaticCell::new(); 241 | #[deny(unused_attributes)] 242 | let (x,) = STATIC_CELL.uninit().write(($val,)); 243 | x 244 | }}; 245 | } 246 | 247 | #[cfg(test)] 248 | mod tests { 249 | use crate::StaticCell; 250 | 251 | #[test] 252 | fn test_static_cell() { 253 | static CELL: StaticCell = StaticCell::new(); 254 | let val: &'static u32 = CELL.init(42u32); 255 | assert_eq!(*val, 42); 256 | } 257 | 258 | #[cfg(feature = "nightly")] 259 | #[test] 260 | fn test_make_static() { 261 | let val: &'static u32 = make_static!(42u32); 262 | assert_eq!(*val, 42); 263 | } 264 | } 265 | --------------------------------------------------------------------------------