Use arc_swap to implement AtomicStr (#72)

* Use `arc_swap` to implement `AtomicStr`

The previous implementation allowed use-after-free in a multi-threaded
context. This PR fixes the problem by using `ArcSwap`, which is
implements thread-safe swapping of `Arc`s, and is widely used.

* Use `triomphe::Arc` to mitigate performance losses

This change replaces `std::sync::Arc` with `triomphe::Arc`. The latter
has no weak references, and is a lot faster because of that.

* Update atomic_str.rs

* Update lib.rs

* Update lib.rs

---------

Co-authored-by: Jason Lee <huacnlee@gmail.com>

README.md

@@ -192,7 +192,7 @@ You can use `rust_i18n::set_locale` to set the global locale at runtime, so that
 rust_i18n::set_locale("zh-CN");
 
 let locale = rust_i18n::locale();
-assert_eq!(*locale, "zh-CN");
+assert_eq!(&*locale, "zh-CN");
 ```
 
 ### Extend Backend

crates/support/Cargo.toml

@@ -8,6 +8,7 @@ repository = "https://github.com/longbridgeapp/rust-i18n"
 version = "3.0.0"
 
 [dependencies]
+arc-swap = "1.6.0"
 globwalk = "0.8.1"
 once_cell = "1.10.0"
 proc-macro2 = "1.0"
@@ -18,3 +19,4 @@ toml = "0.7.4"
 normpath = "1.1.1"
 lazy_static = "1"
 regex = "1"
+triomphe = { version = "0.1.11", features = ["arc-swap"] }

crates/support/src/atomic_str.rs

@@ -1,80 +1,65 @@
 use std::fmt;
-use std::sync::atomic::{AtomicPtr, Ordering};
-use std::sync::Arc;
+use std::ops::Deref;
+
+use arc_swap::{ArcSwapAny, Guard};
+use triomphe::Arc;
 
 /// A thread-safe atomically reference-counting string.
-pub struct AtomicStr(AtomicPtr<String>);
+pub struct AtomicStr(ArcSwapAny<Arc<String>>);
+
+/// A thread-safe view the string that was stored when `AtomicStr::as_str()` was called.
+struct GuardedStr(Guard<Arc<String>>);
+
+impl Deref for GuardedStr {
+    type Target = str;
+
+    fn deref(&self) -> &Self::Target {
+        self.0.as_str()
+    }
+}
 
 impl AtomicStr {
     /// Create a new `AtomicStr` with the given value.
-    pub fn new(value: impl Into<String>) -> Self {
+    pub fn new(value: &str) -> Self {
         let arced = Arc::new(value.into());
-        Self(AtomicPtr::new(Arc::into_raw(arced) as _))
+        Self(ArcSwapAny::new(arced))
     }
 
     /// Get the string slice.
-    pub fn as_str(&self) -> &str {
-        unsafe {
-            let arced_ptr = self.0.load(Ordering::SeqCst);
-            assert!(!arced_ptr.is_null());
-            &*arced_ptr
-        }
-    }
-
-    /// Get the cloned inner `Arc<String>`.
-    pub fn clone_string(&self) -> Arc<String> {
-        unsafe {
-            let arced_ptr = self.0.load(Ordering::SeqCst);
-            assert!(!arced_ptr.is_null());
-            Arc::increment_strong_count(arced_ptr);
-            Arc::from_raw(arced_ptr)
-        }
+    pub fn as_str(&self) -> impl Deref<Target = str> {
+        GuardedStr(self.0.load())
     }
 
-    /// Replaces the value at self with src, returning the old value, without dropping either.
-    pub fn replace(&self, src: impl Into<String>) -> Arc<String> {
-        unsafe {
-            let arced_new = Arc::new(src.into());
-            let arced_old_ptr = self.0.swap(Arc::into_raw(arced_new) as _, Ordering::SeqCst);
-            assert!(!arced_old_ptr.is_null());
-            Arc::from_raw(arced_old_ptr)
-        }
+    /// Replaces the value at self with src.
+    pub fn replace(&self, src: impl Into<String>) {
+        let arced = Arc::new(src.into());
+        self.0.store(arced);
     }
 }
 
-impl Drop for AtomicStr {
-    fn drop(&mut self) {
-        unsafe {
-            let arced_ptr = self.0.swap(std::ptr::null_mut(), Ordering::SeqCst);
-            assert!(!arced_ptr.is_null());
-            let _ = Arc::from_raw(arced_ptr);
-        }
+impl From<&str> for AtomicStr {
+    fn from(value: &str) -> Self {
+        Self::new(value)
     }
 }
 
-impl AsRef<str> for AtomicStr {
-    fn as_ref(&self) -> &str {
-        self.as_str()
+impl fmt::Display for AtomicStr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.as_str())
     }
 }
 
-impl<T> From<T> for AtomicStr
-where
-    T: Into<String>,
-{
-    fn from(value: T) -> Self {
-        Self::new(value)
-    }
-}
+#[cfg(test)]
+mod tests {
+    use super::*;
 
-impl From<&AtomicStr> for Arc<String> {
-    fn from(value: &AtomicStr) -> Self {
-        value.clone_string()
+    fn test_str(s: &str) {
+        assert_eq!(s, "hello");
     }
-}
 
-impl fmt::Display for AtomicStr {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.as_str())
+    #[test]
+    fn test_atomic_str() {
+        let s = AtomicStr::from("hello");
+        test_str(&s.as_str());
     }
 }

src/lib.rs

@@ -1,7 +1,8 @@
 #![doc = include_str!("../README.md")]
 
+use std::ops::Deref;
+
 use once_cell::sync::Lazy;
-use std::sync::Arc;
 
 #[doc(hidden)]
 pub use once_cell;
@@ -16,8 +17,8 @@ pub fn set_locale(locale: &str) {
 }
 
 /// Get current locale
-pub fn locale() -> Arc<String> {
-    CURRENT_LOCALE.clone_string()
+pub fn locale() -> impl Deref<Target = str> {
+    CURRENT_LOCALE.as_str()
 }
 
 /// Replace patterns and return a new string.
@@ -110,7 +111,7 @@ pub fn replace_patterns(input: &str, patterns: &[&str], values: &[String]) -> St
 macro_rules! t {
     // t!("foo")
     ($key:expr) => {
-        crate::_rust_i18n_translate(rust_i18n::locale().as_str(), $key)
+        crate::_rust_i18n_translate(&rust_i18n::locale(), $key)
     };
 
     // t!("foo", locale = "en")
@@ -184,7 +185,7 @@ mod tests {
 
     #[test]
     fn test_locale() {
-        assert_locale_type(locale().as_str(), CURRENT_LOCALE.as_str());
-        assert_locale_type(&locale(), CURRENT_LOCALE.as_str());
+        assert_locale_type(&locale(), &CURRENT_LOCALE.as_str());
+        assert_eq!(locale().deref(), "en");
     }
 }

tests/multi_threading.rs

@@ -0,0 +1,34 @@
+use std::ops::Add;
+use std::thread::spawn;
+use std::time::{Duration, Instant};
+
+use rust_i18n::{set_locale, t};
+
+rust_i18n::i18n!("locales", fallback = "en");
+
+#[test]
+fn test_load_and_store() {
+    let end = Instant::now().add(Duration::from_secs(3));
+    let store = spawn(move || {
+        let mut i = 0u32;
+        while Instant::now() < end {
+            for _ in 0..100 {
+                i = i.wrapping_add(1);
+                if i % 2 == 0 {
+                    set_locale(&format!("en-{i}"));
+                } else {
+                    set_locale(&format!("fr-{i}"));
+                }
+            }
+        }
+    });
+    let load = spawn(move || {
+        while Instant::now() < end {
+            for _ in 0..100 {
+                t!("hello");
+            }
+        }
+    });
+    store.join().unwrap();
+    load.join().unwrap();
+}