made multithreaded deterministic

Author: zphrs

Cargo.lock

@@ -16,6 +16,7 @@ features = ["std", "sys_rng"]
 rustdoc-args = ["--cfg", "getrandom_backend=\"extern_impl\""]
 
 [features]
+default = ["unsafe_deterministic_testing"]
 # Implement From<getrandom::Error> for std::io::Error and
 # use std to retrieve OS error descriptions
 std = []

Cargo.toml

@@ -11,22 +11,32 @@ use crate::Error;
 use chacha20::ChaCha12Rng;
 use core::mem::MaybeUninit;
 use rand_core::{Rng, SeedableRng};
-use std::sync::{Mutex, OnceLock};
+use std::{
+    collections::HashMap,
+    sync::{Mutex, OnceLock},
+};
 
 /// The RNG, initialised exactly once on first use.
-static RNG: OnceLock<Mutex<ChaCha12Rng>> = OnceLock::new();
+static RNG: OnceLock<Mutex<HashMap<std::thread::ThreadId, ChaCha12Rng>>> = OnceLock::new();
 
 #[inline]
 pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    let rng = RNG.get_or_init(|| Mutex::new(ChaCha12Rng::from_seed([42u8; 32])));
+    // get current thread id
+    let id = std::thread::current().id();
+
+    let rng = RNG.get_or_init(|| HashMap::new().into());
 
     let mut guard = rng.lock().unwrap();
 
+    let entry = guard
+        .entry(id)
+        .or_insert_with(|| ChaCha12Rng::from_seed([42u8; 32]));
+
     // SAFETY: `fill_bytes` fully overwrites every byte of the slice, so
     // treating uninitialized `MaybeUninit<u8>` as `u8` for the purpose of
     // writing (never reading) is sound.
     let dest_init = unsafe { dest.assume_init_mut() };
-    guard.fill_bytes(dest_init);
+    entry.fill_bytes(dest_init);
 
     Ok(())
 }
@@ -48,4 +58,32 @@ mod tests {
             buf
         );
     }
+    use std::thread;
+    #[test]
+    fn test_deterministic_multithread() {
+        thread::spawn(|| {
+            let mut buf = [0u8; 32];
+            crate::fill(&mut buf).unwrap();
+            assert_eq!(
+                [
+                    0x1b, 0x8c, 0x20, 0xcd, 0xe2, 0xdb, 0xb4, 0x3c, 0xd3, 0xc7, 0x9, 0xb2, 0x90,
+                    0xac, 0x50, 0xdc, 0xd2, 0xbe, 0x2a, 0x87, 0xa3, 0xa2, 0x45, 0x44, 0xb5, 0xa5,
+                    0x10, 0x9b, 0xc7, 0x6e, 0xa7, 0xfb,
+                ],
+                buf
+            );
+        });
+        thread::spawn(|| {
+            let mut buf = [0u8; 32];
+            crate::fill(&mut buf).unwrap();
+            assert_eq!(
+                [
+                    0x1b, 0x8c, 0x20, 0xcd, 0xe2, 0xdb, 0xb4, 0x3c, 0xd3, 0xc7, 0x9, 0xb2, 0x90,
+                    0xac, 0x50, 0xdc, 0xd2, 0xbe, 0x2a, 0x87, 0xa3, 0xa2, 0x45, 0x44, 0xb5, 0xa5,
+                    0x10, 0x9b, 0xc7, 0x6e, 0xa7, 0xfb,
+                ],
+                buf
+            );
+        });
+    }
 }