Implement a cloneable shared counter. (#407) r=nalexander

core/src/counter.rs

@@ -0,0 +1,47 @@
+// Copyright 2016 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+use std::rc::Rc;
+
+use std::sync::atomic::{
+    AtomicUsize,
+    Ordering,
+};
+
+#[derive(Clone)]
+pub struct RcCounter {
+    c: Rc<AtomicUsize>,
+}
+
+impl RcCounter {
+    pub fn new() -> Self {
+        RcCounter { c: Rc::new(AtomicUsize::new(0)) }
+    }
+
+    pub fn next(&self) -> usize {
+        self.c.fetch_add(1, Ordering::SeqCst)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::RcCounter;
+
+    #[test]
+    fn test_rc_counter() {
+        let c = RcCounter::new();
+        assert_eq!(c.next(), 0);
+        assert_eq!(c.next(), 1);
+
+        let d = c.clone();
+        assert_eq!(d.next(), 2);
+        assert_eq!(c.next(), 3);
+    }
+}

core/src/lib.rs

@@ -488,4 +488,5 @@ mod test {
 }
 
 pub mod intern_set;
+pub mod counter;
 pub mod util;

core/src/util.rs

@@ -1,4 +1,3 @@
-
 // Copyright 2016 Mozilla
 //
 // Licensed under the Apache License, Version 2.0 (the "License"); you may not use