Add weak_count and strong_count to Rc and Arc

src/liballoc/arc.rs

@@ -119,6 +119,16 @@ impl<T> Arc<T> {
     }
 }
 
+/// Get the number of weak references to this value.
+#[inline]
+#[experimental]
+pub fn weak_count<T>(this: &Arc<T>) -> uint { this.inner().weak.load(atomic::SeqCst) - 1 }
+
+/// Get the number of strong references to this value.
+#[inline]
+#[experimental]
+pub fn strong_count<T>(this: &Arc<T>) -> uint { this.inner().strong.load(atomic::SeqCst) }
+
 #[unstable = "waiting on stability of Clone"]
 impl<T> Clone for Arc<T> {
     /// Duplicate an atomically reference counted wrapper.
@@ -321,7 +331,7 @@ mod tests {
     use std::sync::atomic;
     use std::task;
     use std::vec::Vec;
-    use super::{Arc, Weak};
+    use super::{Arc, Weak, weak_count, strong_count};
     use std::sync::Mutex;
 
     struct Canary(*mut atomic::AtomicUint);
@@ -465,6 +475,49 @@ mod tests {
         drop(arc_weak);
     }
 
+    #[test]
+    fn test_strong_count() {
+        let a = Arc::new(0u32);
+        assert!(strong_count(&a) == 1);
+        let w = a.downgrade();
+        assert!(strong_count(&a) == 1);
+        let b = w.upgrade().expect("");
+        assert!(strong_count(&b) == 2);
+        assert!(strong_count(&a) == 2);
+        drop(w);
+        drop(a);
+        assert!(strong_count(&b) == 1);
+        let c = b.clone();
+        assert!(strong_count(&b) == 2);
+        assert!(strong_count(&c) == 2);
+    }
+
+    #[test]
+    fn test_weak_count() {
+        let a = Arc::new(0u32);
+        assert!(strong_count(&a) == 1);
+        assert!(weak_count(&a) == 0);
+        let w = a.downgrade();
+        assert!(strong_count(&a) == 1);
+        assert!(weak_count(&a) == 1);
+        let x = w.clone();
+        assert!(weak_count(&a) == 2);
+        drop(w);
+        drop(x);
+        assert!(strong_count(&a) == 1);
+        assert!(weak_count(&a) == 0);
+        let c = a.clone();
+        assert!(strong_count(&a) == 2);
+        assert!(weak_count(&a) == 0);
+        let d = c.downgrade();
+        assert!(weak_count(&c) == 1);
+        assert!(strong_count(&c) == 2);
+
+        drop(a);
+        drop(c);
+        drop(d);
+    }
+
     #[test]
     fn show_arc() {
         let a = Arc::new(5u32);

src/liballoc/rc.rs

@@ -213,15 +213,24 @@ impl<T> Rc<T> {
     }
 }
 
+/// Get the number of weak references to this value.
+#[inline]
+#[experimental]
+pub fn weak_count<T>(this: &Rc<T>) -> uint { this.weak() - 1 }
+
+/// Get the number of strong references to this value.
+#[inline]
+#[experimental]
+pub fn strong_count<T>(this: &Rc<T>) -> uint { this.strong() }
+
 /// Returns true if the `Rc` currently has unique ownership.
 ///
 /// Unique ownership means that there are no other `Rc` or `Weak` values
 /// that share the same contents.
 #[inline]
 #[experimental]
 pub fn is_unique<T>(rc: &Rc<T>) -> bool {
-    // note that we hold both a strong and a weak reference
-    rc.strong() == 1 && rc.weak() == 1
+    weak_count(rc) == 0 && strong_count(rc) == 1
 }
 
 /// Unwraps the contained value if the `Rc` has unique ownership.
@@ -489,7 +498,7 @@ impl<T> RcBoxPtr<T> for Weak<T> {
 #[cfg(test)]
 #[allow(experimental)]
 mod tests {
-    use super::{Rc, Weak};
+    use super::{Rc, Weak, weak_count, strong_count};
     use std::cell::RefCell;
     use std::option::{Option, Some, None};
     use std::result::{Err, Ok};
@@ -566,6 +575,40 @@ mod tests {
         assert!(super::is_unique(&x));
     }
 
+    #[test]
+    fn test_strong_count() {
+        let a = Rc::new(0u32);
+        assert!(strong_count(&a) == 1);
+        let w = a.downgrade();
+        assert!(strong_count(&a) == 1);
+        let b = w.upgrade().expect("upgrade of live rc failed");
+        assert!(strong_count(&b) == 2);
+        assert!(strong_count(&a) == 2);
+        drop(w);
+        drop(a);
+        assert!(strong_count(&b) == 1);
+        let c = b.clone();
+        assert!(strong_count(&b) == 2);
+        assert!(strong_count(&c) == 2);
+    }
+
+    #[test]
+    fn test_weak_count() {
+        let a = Rc::new(0u32);
+        assert!(strong_count(&a) == 1);
+        assert!(weak_count(&a) == 0);
+        let w = a.downgrade();
+        assert!(strong_count(&a) == 1);
+        assert!(weak_count(&a) == 1);
+        drop(w);
+        assert!(strong_count(&a) == 1);
+        assert!(weak_count(&a) == 0);
+        let c = a.clone();
+        assert!(strong_count(&a) == 2);
+        assert!(weak_count(&a) == 0);
+        drop(c);
+    }
+
     #[test]
     fn try_unwrap() {
         let x = Rc::new(3u);