Provide immutable interface for local counter (tikv#251)

Signed-off-by: Breezewish <[email protected]>

Author: breezewish

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 0.7.0
+
+- Provide immutable interface for local counters.
+
 ## 0.6.1
 
 - Fix compile error when ProtoBuf feature is not enabled (#240).

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "prometheus"
-version = "0.6.1"
+version = "0.7.0"
 license = "Apache-2.0"
 keywords = ["prometheus", "metrics"]
 authors = ["[email protected]", "[email protected]", "[email protected]"]

README.md

@@ -13,7 +13,7 @@ The main Structures and APIs are ported from [Go client](https://github.com/prom
 
     ```toml
     [dependencies]
-    prometheus = "0.6"
+    prometheus = "0.7"
     ```
 
 + Add this to your crate in `lib.rs`:

src/counter.rs

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::cell::RefCell;
 use std::collections::HashMap;
 use std::marker::PhantomData;
 use std::sync::Arc;
@@ -170,7 +171,7 @@ impl<P: Atomic> GenericCounterVec<P> {
 /// and [`LocalIntCounter`](::local::LocalIntCounter).
 pub struct GenericLocalCounter<P: Atomic> {
     counter: GenericCounter<P>,
-    val: P::T,
+    val: RefCell<P::T>,
 }
 
 /// An unsync [`Counter`](::Counter).
@@ -184,7 +185,7 @@ impl<P: Atomic> GenericLocalCounter<P> {
     fn new(counter: GenericCounter<P>) -> Self {
         Self {
             counter,
-            val: P::T::from_i64(0),
+            val: RefCell::new(P::T::from_i64(0)),
         }
     }
 
@@ -194,31 +195,31 @@ impl<P: Atomic> GenericLocalCounter<P> {
     ///
     /// Panics in debug build if the value is < 0.
     #[inline]
-    pub fn inc_by(&mut self, v: P::T) {
+    pub fn inc_by(&self, v: P::T) {
         debug_assert!(v >= P::T::from_i64(0));
-        self.val += v;
+        *self.val.borrow_mut() += v;
     }
 
     /// Increase the local counter by 1.
     #[inline]
-    pub fn inc(&mut self) {
-        self.val += P::T::from_i64(1);
+    pub fn inc(&self) {
+        *self.val.borrow_mut() += P::T::from_i64(1);
     }
 
     /// Return the local counter value.
     #[inline]
     pub fn get(&self) -> P::T {
-        self.val
+        *self.val.borrow()
     }
 
     /// Flush the local metrics to the [`Counter`](::Counter).
     #[inline]
-    pub fn flush(&mut self) {
-        if self.val == P::T::from_i64(0) {
+    pub fn flush(&self) {
+        if *self.val.borrow() == P::T::from_i64(0) {
             return;
         }
-        self.counter.inc_by(self.val);
-        self.val = P::T::from_i64(0);
+        self.counter.inc_by(*self.val.borrow());
+        *self.val.borrow_mut() = P::T::from_i64(0);
     }
 }
 
@@ -327,8 +328,8 @@ mod tests {
     #[test]
     fn test_local_counter() {
         let counter = Counter::new("counter", "counter helper").unwrap();
-        let mut local_counter1 = counter.local();
-        let mut local_counter2 = counter.local();
+        let local_counter1 = counter.local();
+        let local_counter2 = counter.local();
 
         local_counter1.inc();
         local_counter2.inc();
@@ -345,7 +346,7 @@ mod tests {
     #[test]
     fn test_int_local_counter() {
         let counter = IntCounter::new("foo", "bar").unwrap();
-        let mut local_counter = counter.local();
+        let local_counter = counter.local();
 
         local_counter.inc();
         assert_eq!(local_counter.get(), 1);
@@ -524,7 +525,7 @@ mod tests {
     #[should_panic(expected = "assertion failed")]
     fn test_local_counter_negative_inc() {
         let counter = Counter::new("foo", "bar").unwrap();
-        let mut local = counter.local();
+        let local = counter.local();
         local.inc_by(-42.0);
     }
 
@@ -541,7 +542,7 @@ mod tests {
     #[should_panic(expected = "assertion failed")]
     fn test_int_local_counter_negative_inc() {
         let counter = IntCounter::new("foo", "bar").unwrap();
-        let mut local = counter.local();
+        let local = counter.local();
         local.inc_by(-42);
     }
 }