Merge pull request #662 from l1npengtul/stable_hash

New Static Hash Feature

.github/workflows/build.yml

@@ -96,6 +96,8 @@ jobs:
     continue-on-error: ${{matrix.experimental}}
     strategy:
       matrix:
+        flags:
+          - ""
         include:
           - {os: ubuntu-latest, flags: "--profile unix", experimental: false}
           - {os: windows-latest, flags: "--profile windows", experimental: true}

.gitignore

@@ -8,3 +8,6 @@ Rhai.toml
 **/*.bat
 doc/rhai-sync.json
 doc/rhai.json
+.idea/
+.idea
+.idea/*

build.rs

@@ -8,7 +8,6 @@ fn main() {
     // Tell Cargo that if the given environment variable changes, to rerun this build script.
     println!("cargo:rerun-if-changed=build.template");
     println!("cargo:rerun-if-env-changed=RHAI_AHASH_SEED");
-
     let mut contents = String::new();
 
     File::open("build.template")
@@ -20,8 +19,8 @@ fn main() {
 
     contents = contents.replace("{{AHASH_SEED}}", &seed);
 
-    File::create("src/config.rs")
+    File::create("src/config/hashing_env.rs")
         .expect("cannot create `config.rs`")
-        .write(contents.as_bytes())
+        .write_all(contents.as_bytes())
-        .expect("cannot write to `config.rs`");
+        .expect("cannot write to `config/hashing_env.rs`");
 }

build.template

@@ -1,7 +1,2 @@
-//! Configuration settings for this Rhai build
+// This file is automatically set during build time by build.rs and build.template.
-//!
+pub(crate) const AHASH_SEED: Option<[u64; 4]> = {{AHASH_SEED}};
-//! This file is auto-generated from `build.template`
-
-/// Fixed hashing seeds for stable hashing.
-/// Set to [`None`] to disable stable hashing.
-pub const AHASH_SEED: Option<[u64; 4]> = {{AHASH_SEED}};

src/config.rs

@@ -1,7 +0,0 @@
-//! Configuration settings for this Rhai build
-//!
-//! This file is auto-generated from `build.template`
-
-/// Fixed hashing seeds for stable hashing.
-/// Set to [`None`] to disable stable hashing.
-pub const AHASH_SEED: Option<[u64; 4]> = None;

src/config/hashing.rs

@@ -0,0 +1,183 @@
+//! Fixed hashing seeds for stable hashing.
+//!
+//! Set to [`None`] to disable stable hashing.
+//!
+//! See [`set_rhai_ahash_seed`] for more.
+//!
+//! Alternatively, You can also set this at compile time by setting the `RHAI_AHASH_SEED`
+//! environment variable instead.
+//!
+//! E.g. `env RHAI_AHASH_SEED ="[236,800,954,213]"`
+// [236,800,954,213], haha funny yume nikki reference epic uboachan face numberworld nexus moment 100
+
+use crate::config::hashing_env;
+use core::{
+    cell::UnsafeCell,
+    marker::PhantomData,
+    mem::MaybeUninit,
+    panic::{RefUnwindSafe, UnwindSafe},
+    sync::atomic::{AtomicBool, AtomicUsize, Ordering},
+};
+
+// omg its hokma from record team here to record our locks
+// what does this do?
+// so what this does is keep track of a global address in memory that acts as a global lock
+// i stole this from crossbeam so read their docs for more
+struct HokmaLock {
+    lock: AtomicUsize,
+}
+
+impl HokmaLock {
+    pub const fn new() -> Self {
+        Self {
+            lock: AtomicUsize::new(0),
+        }
+    }
+
+    pub fn write(&'static self) -> WhenTheHokmaSupression {
+        loop {
+            let previous = self.lock.swap(1, Ordering::SeqCst);
+
+            if previous != 1 {
+                return WhenTheHokmaSupression {
+                    hokma: self,
+                    state: previous,
+                };
+            }
+        }
+    }
+}
+
+struct WhenTheHokmaSupression {
+    hokma: &'static HokmaLock,
+
+    state: usize,
+}
+
+impl WhenTheHokmaSupression {
+    pub fn the_price_of_silence(self) {
+        self.hokma.lock.store(self.state, Ordering::SeqCst);
+
+        core::mem::forget(self)
+    }
+}
+
+impl Drop for WhenTheHokmaSupression {
+    fn drop(&mut self) {
+        self.hokma
+            .lock
+            .store(self.state.wrapping_add(2), Ordering::SeqCst)
+    }
+}
+
+fn hokmalock(address: usize) -> &'static HokmaLock {
+    const LEN: usize = 787;
+    const LCK: HokmaLock = HokmaLock::new();
+    static RECORDS: [HokmaLock; LEN] = [LCK; LEN];
+
+    &RECORDS[address % LEN]
+}
+
+// Safety: lol, there is a reason its called "SusLock<T>"
+struct SusLock<T>
+where
+    T: 'static + Copy,
+{
+    initalized: AtomicBool,
+    data: UnsafeCell<MaybeUninit<T>>,
+    _marker: PhantomData<T>,
+}
+
+impl<T> SusLock<T>
+where
+    T: 'static + Copy,
+{
+    pub const fn new() -> SusLock<T> {
+        SusLock {
+            initalized: AtomicBool::new(false),
+            data: UnsafeCell::new(MaybeUninit::uninit()),
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn get(&self) -> Option<T> {
+        if self.initalized.load(Ordering::SeqCst) {
+            let hokma = hokmalock(unsafe { core::mem::transmute(self.data.get()) });
+            // we forgo the optimistic read, because we don't really care
+            let guard = hokma.write();
+            let val = {
+                let cast: *const T = self.data.get().cast();
+                unsafe { cast.read() }
+            };
+            guard.the_price_of_silence();
+            Some(val)
+        } else {
+            return None;
+        }
+    }
+
+    pub fn get_or_init(&self, f: impl FnOnce() -> T) -> Option<T> {
+        let value = f();
+        if !self.initalized.load(Ordering::SeqCst) {
+            self.initalized.store(true, Ordering::SeqCst);
+            let hokma = hokmalock(unsafe { core::mem::transmute(self.data.get()) });
+            hokma.write();
+            unsafe {
+                self.data.get().write(MaybeUninit::new(value));
+            }
+        }
+
+        self.get()
+    }
+
+    pub fn set(&self, value: T) -> Result<(), T> {
+        if self.initalized.load(Ordering::SeqCst) {
+            Err(value)
+        } else {
+            let _ = self.get_or_init(|| value);
+            Ok(())
+        }
+    }
+}
+
+unsafe impl<T: Sync + Send> Sync for SusLock<T> where T: 'static + Copy {}
+unsafe impl<T: Send> Send for SusLock<T> where T: 'static + Copy {}
+impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SusLock<T> where T: 'static + Copy {}
+
+impl<T> Drop for SusLock<T>
+where
+    T: 'static + Copy,
+{
+    fn drop(&mut self) {
+        if self.initalized.load(Ordering::SeqCst) {
+            unsafe { (&mut *self.data.get()).assume_init_drop() };
+        }
+    }
+}
+
+static AHASH_SEED: SusLock<Option<[u64; 4]>> = SusLock::new();
+
+// #[doc(cfg(feature = "stable_hash"))]
+/// Sets the Rhai Ahash seed. This is used to hash functions and the like.
+///
+/// This is a global variable, and thus will affect every Rhai instance.
+/// This should not be used _unless_ you know you need it.
+///
+/// # Warnings
+/// - You can only call this function **ONCE** for the whole of your program execution.
+/// - You should gracefully handle the `Err(())`.
+/// - You **MUST** call this before **ANY** Rhai operation occurs (e.g. creating an [`Engine`]).
+///
+/// # Errors
+/// This will error if the AHashSeed is already set.
+pub fn set_ahash_seed(new_seed: Option<[u64; 4]>) -> Result<(), Option<[u64; 4]>> {
+    AHASH_SEED.set(new_seed)
+}
+
+/// Gets the current Rhai Ahash Seed. If the seed is not yet defined, this will automatically set a seed.
+/// The default seed is not stable and may change between versions.
+///
+/// See [`set_rhai_ahash_seed`] for more.
+pub fn get_ahash_seed() -> Option<[u64; 4]> {
+    AHASH_SEED.get_or_init(|| hashing_env::AHASH_SEED).flatten()
+}

src/config/hashing_env.rs

@@ -0,0 +1,2 @@
+// This file is automatically set during build time by build.rs and build.template.
+pub(crate) const AHASH_SEED: Option<[u64; 4]> = None;

src/config/mod.rs

@@ -0,0 +1,4 @@
+//! Contains Configuration for Rhai.
+
+pub mod hashing;
+mod hashing_env;

src/func/hashing.rs

@@ -77,7 +77,7 @@ impl BuildHasher for StraightHasherBuilder {
 #[inline(always)]
 #[must_use]
 pub fn get_hasher() -> ahash::AHasher {
-    match config::AHASH_SEED {
+    match config::hashing::get_ahash_seed() {
         Some([seed1, seed2, seed3, seed4]) if seed1 | seed2 | seed3 | seed4 != 0 => {
             ahash::RandomState::with_seeds(seed1, seed2, seed3, seed4).build_hasher()
         }

src/lib.rs

@@ -83,7 +83,7 @@ use std::prelude::v1::*;
 // Internal modules
 mod api;
 mod ast;
-mod config;
+pub mod config;
 mod engine;
 mod eval;
 mod func;