initial commit

.editorconfig

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+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+[*]
+indent_style = tab
+indent_size = 4
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.yaml]
+indent_style = space
+indent_size = 2

.github/workflows/ci.yaml

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+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu, windows ]
+    runs-on: ${{ matrix.os }}-latest
+    name: Test on ${{ matrix.os }}-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo test
+
+  doc:
+    name: Docs
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - uses: dtolnay/install@cargo-docs-rs
+      - run: cargo docs-rs
+

.gitignore

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+/.vscode
+/Cargo.lock
+/target

Cargo.toml

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+[package]
+name = "rcurs"
+version = "0.1.0"
+edition = "2021"
+description = "An oxidized RCU implementation"
+license = "MIT"
+repository = "https://github.com/threadexio/rcurs"
+readme = "README.md"
+keywords = ["rcu", "synchronization", "concurrent", "parallel", "lock-free"]
+categories = ["concurrency"]
+
+[dependencies]
+
+[features]
+default = ["std"]
+
+std = []

LICENSE

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+MIT License
+
+Copyright (c) 2024 1337
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 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.

README.md

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+[`core::hint::spin_loop()`]: https://doc.rust-lang.org/stable/core/hint/fn.spin_loop.html
+[`Condvar`]: https://doc.rust-lang.org/stable/std/sync/struct.Condvar.html
+
+# rcurs
+
+A simple [RCU](https://en.wikipedia.org/wiki/Read-copy-update) with an oxidized interface. Read more at the [docs](https://docs.rs/rcurs).
+
+The crate supports running both with or without the `std` library but has a hard dependency on `alloc`. If your environment allows, you should try to keep the `std` feature enabled as that contains typically more efficient implementations of blocking primitives.
+
+Without the `std` feature, the only way to block is to spin in place using whatever optimization [`core::hint::spin_loop()`] can provide. But with the standard library, blocking is done using [`Condvar`]s. [`Condvar`]s call out to the kernel for blocking. The kernel can then choose what is best, spin itself, or usually give control back to the scheduler to run other processes.
+
+## Features
+
+- `std`: Enable use of primitives in the standard library

rust-toolchain.toml

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+[toolchain]
+channel = "stable"
+profile = "minimal"
+components = ["clippy", "rustfmt"]

rustfmt.toml

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+max_width = 70
+hard_tabs = true
+tab_spaces = 4
+newline_style = "Unix"
+use_small_heuristics = "Off"
+fn_call_width = 60
+attr_fn_like_width = 60
+struct_lit_width = 60
+struct_variant_width = 60
+array_width = 60
+chain_width = 60
+single_line_if_else_max_width = 0
+reorder_imports = true
+reorder_modules = true
+remove_nested_parens = true
+match_arm_leading_pipes = "Never"
+fn_params_layout = "Tall"
+match_block_trailing_comma = true
+edition = "2021"
+merge_derives = true
+use_try_shorthand = true
+use_field_init_shorthand = true
+force_explicit_abi = true

src/cfg.rs

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+macro_rules! cfg_std {
+	($($item:item)*) => {
+		$(
+			#[cfg(feature = "std")]
+			$item
+		)*
+	};
+}
+
+pub(crate) use cfg_std;

src/lib.rs

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+//! [`Rcu`] or Read-Copy-Update is a mechanism that allows sharing and updating
+//! a piece of data while multiple parallel code blocks have access to it in a
+//! lock-free manner. A better explanation is available at the [kernel docs](https://www.kernel.org/doc/html/latest/RCU/whatisRCU.html)
+//! or even [Wikipedia](https://en.wikipedia.org/wiki/Read-copy-update).
+//!
+//! Internally, an RCU is composed of an _atomic_ pointer (the atomic part
+//! is important) to some data along with the number of currently active
+//! references to it. Something like a garbage-collector (but obviously way
+//! simpler). So when you want to get at the actual data, you simply increment
+//! the counter of references by one and decrement it when you are done. This
+//! is the easy part, now how do we update the value without locking and
+//! without messing up anyone already working? Well, each reference does not
+//! keep a pointer to the RCU, but instead copies the value of the atomic
+//! pointer when it is created. The key is that the pointer to the data is
+//! atomic. So we simply create a new copy of data, make our changes to that
+//! copy, and then atomically update the pointer. This way we ensure that a
+//! reference that is created at the same time as we update it uses either:
+//! the old value or the new value. In any case, it does not end up with an
+//! invalid pointer. Because we are a model programmer, we must also not
+//! forget to clean up the old data which is effectively outdated and useless.
+//! But we can't just clean up the old data: there might be references
+//! to it from before we did the update. Ah, so we will wait for the code
+//! with old references to drop them, and because we swapped the pointer before,
+//! no new references can get access to the old data. After waiting and ensuring
+//! there are no remaining references to the old data, we can now safely free
+//! it without worry.
+//!
+//! # Example
+//!
+//! ```rust,no_run
+//! use std::thread;
+//! use std::time::Duration;
+//!
+//! type Rcu<T> = rcurs::Rcu<T, rcurs::Spin>;
+//!
+//! #[derive(Debug, Clone, PartialEq, Eq)]
+//! struct User {
+//!     uid: i32,
+//!     gid: i32,
+//! }
+//!
+//! fn setugid(user: &Rcu<User>, uid: i32, gid: i32) {
+//!     let mut new = user.get().clone();
+//!
+//!     if new.uid == uid && new.gid == gid {
+//!         return;
+//!     }
+//!
+//!     new.uid = uid;
+//!     new.gid = gid;
+//!
+//!     user.update(new);
+//! }
+//!
+//! // Basically a `sleep`` function that holds onto `user` and prints it after
+//! // `sec` seconds have passed.
+//! fn compute(user: &Rcu<User>, id: &str, sec: u64) {
+//!     let user = user.get();
+//!     thread::sleep(Duration::from_secs(sec));
+//!     println!("compute[{id}]: finish work for {}:{}", user.uid, user.gid);
+//! }
+//!
+//! fn thread_1(user: &Rcu<User>) {
+//!     compute(user, "1", 3);
+//!
+//!     // This call will update `user`.
+//!     setugid(user, 1000, 1000);
+//!
+//!     compute(user, "3", 4);
+//! }
+//!
+//! fn thread_2(user: &Rcu<User>) {
+//!     // The following compute call will always see the `User { uid: 0, gid: 0}`
+//!     // as the `setugid` call happens 3 seconds after it has started executing.
+//!     compute(user, "2", 5);
+//! }
+//!
+//! fn main() {
+//!     let user = Rcu::new(User { uid: 0, gid: 0 });
+//!
+//!     thread::scope(|scope| {
+//!         scope.spawn(|| thread_1(&user));
+//!         scope.spawn(|| thread_2(&user));
+//!     });
+//! }
+//! ```
+#![deny(missing_docs)]
+#![warn(
+	clippy::all,
+	clippy::correctness,
+	clippy::pedantic,
+	clippy::cargo,
+	clippy::nursery,
+	clippy::perf,
+	clippy::style
+)]
+#![allow(
+	clippy::missing_panics_doc,
+	clippy::significant_drop_tightening,
+	clippy::needless_lifetimes
+)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+mod cfg;
+
+mod notify;
+mod rcu;
+
+#[doc(inline)]
+pub use self::notify::*;
+
+#[doc(inline)]
+pub use self::rcu::{Guard, Rcu};

src/notify/blocking.rs

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+use super::Notify;
+
+use std::sync::{Condvar, Mutex};
+
+/// A [`Notify`] backend that uses a [`Condvar`] to achieve true blocking.
+pub struct Blocking {
+    /* Keep track of both whether notify was called and how many waiter there are.
+     * This way, the waiter who wakes up last can know to reset the `notified` flag
+     * again to prepare for the next `notify`.
+     */
+    lock: Mutex<(bool, u8)>,
+    var: Condvar,
+}
+
+impl Notify for Blocking {
+    fn new() -> Self {
+        Self {
+            lock: Mutex::new((false, 0)),
+            var: Condvar::new(),
+        }
+    }
+
+    fn wait(&self) {
+        let mut guard = self.lock.lock().unwrap();
+        guard.1 += 1;
+
+        let mut guard = self
+            .var
+            .wait_while(guard, |(notified, _)| !*notified)
+            .unwrap();
+        guard.1 -= 1;
+
+        if guard.1 == 0 {
+            guard.0 = false;
+        }
+    }
+
+    fn notify(&self) {
+        let mut guard = self.lock.lock().unwrap();
+        guard.0 = true;
+        self.var.notify_all();
+    }
+}
+
+impl Default for Blocking {
+    fn default() -> Self {
+        Self::new()
+    }
+}