src/metrics/gauge: Implement Gauge::dec and Gauge::dec_by (prometheus#30

)

Signed-off-by: ackintosh <sora.akatsuki@gmail.com>

CHANGELOG.md

@@ -4,15 +4,20 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [0.13.1] - unreleased
+## [0.14.0] - unreleased
 
 ### Changed
 
 - Update to `itoa` `v1`. See [PR 28].
 - Update to `dtoa` `v1`. See [PR 27].
 
+### Added
+
+- Implement `Gauge::dec` and `Gauge::dec_by`. See [PR 30].
+
 [PR 28]: https://github.com/mxinden/rust-open-metrics-client/pull/28
 [PR 27]: https://github.com/mxinden/rust-open-metrics-client/pull/27
+[PR 30]: https://github.com/mxinden/rust-open-metrics-client/pull/30
 
 ## [0.13.0] - 2021-11-21
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "open-metrics-client"
-version = "0.13.1"
+version = "0.14.0"
 authors = ["Max Inden <mail@max-inden.de>"]
 edition = "2018"
 description = "Open Metrics client library allowing users to natively instrument applications."

src/metrics/gauge.rs

@@ -70,6 +70,16 @@ impl<N, A: Atomic<N>> Gauge<N, A> {
         self.value.inc_by(v)
     }
 
+    /// Decrease the [`Gauge`] by 1, returning the previous value.
+    pub fn dec(&self) -> N {
+        self.value.dec()
+    }
+
+    /// Decrease the [`Gauge`] by `v`, returning the previous value.
+    pub fn dec_by(&self, v: N) -> N {
+        self.value.dec_by(v)
+    }
+
     /// Sets the [`Gauge`] to `v`, returning the previous value.
     pub fn set(&self, v: N) -> N {
         self.value.set(v)
@@ -94,6 +104,10 @@ pub trait Atomic<N> {
 
     fn inc_by(&self, v: N) -> N;
 
+    fn dec(&self) -> N;
+
+    fn dec_by(&self, v: N) -> N;
+
     fn set(&self, v: N) -> N;
 
     fn get(&self) -> N;
@@ -108,6 +122,14 @@ impl Atomic<u64> for AtomicU64 {
         self.fetch_add(v, Ordering::Relaxed)
     }
 
+    fn dec(&self) -> u64 {
+        self.dec_by(1)
+    }
+
+    fn dec_by(&self, v: u64) -> u64 {
+        self.fetch_sub(v, Ordering::Relaxed)
+    }
+
     fn set(&self, v: u64) -> u64 {
         self.swap(v, Ordering::Relaxed)
     }
@@ -126,6 +148,14 @@ impl Atomic<u32> for AtomicU32 {
         self.fetch_add(v, Ordering::Relaxed)
     }
 
+    fn dec(&self) -> u32 {
+        self.dec_by(1)
+    }
+
+    fn dec_by(&self, v: u32) -> u32 {
+        self.fetch_sub(v, Ordering::Relaxed)
+    }
+
     fn set(&self, v: u32) -> u32 {
         self.swap(v, Ordering::Relaxed)
     }
@@ -155,6 +185,25 @@ impl Atomic<f64> for AtomicU64 {
         old_f64
     }
 
+    fn dec(&self) -> f64 {
+        self.dec_by(1.0)
+    }
+
+    fn dec_by(&self, v: f64) -> f64 {
+        let mut old_u64 = self.load(Ordering::Relaxed);
+        let mut old_f64;
+        loop {
+            old_f64 = f64::from_bits(old_u64);
+            let new = f64::to_bits(old_f64 - v);
+            match self.compare_exchange_weak(old_u64, new, Ordering::Relaxed, Ordering::Relaxed) {
+                Ok(_) => break,
+                Err(x) => old_u64 = x,
+            }
+        }
+
+        old_f64
+    }
+
     fn set(&self, v: f64) -> f64 {
         f64::from_bits(self.swap(f64::to_bits(v), Ordering::Relaxed))
     }
@@ -173,11 +222,15 @@ mod tests {
     use super::*;
 
     #[test]
-    fn inc_and_get() {
+    fn inc_dec_and_get() {
         let gauge: Gauge = Gauge::default();
         assert_eq!(0, gauge.inc());
         assert_eq!(1, gauge.get());
-        assert_eq!(1, gauge.set(10));
+
+        assert_eq!(1, gauge.dec());
+        assert_eq!(0, gauge.get());
+
+        assert_eq!(0, gauge.set(10));
         assert_eq!(10, gauge.get());
     }
 }