Revert "Add: exponential backoff for CAS operations on floats (#1661)"

This reverts commit a934c35.
prometheus · Mar 4, 2025 · 9e567a7 · 9e567a7
1 parent eaf03ef
commit 9e567a7
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Showing 6 changed files with 36 additions and 236 deletions.
diff --git a/prometheus/atomic_update.go b/prometheus/atomic_update.go
diff --git a/prometheus/atomic_update_test.go b/prometheus/atomic_update_test.go
diff --git a/prometheus/counter.go b/prometheus/counter.go
@@ -134,9 +134,13 @@ func (c *counter) Add(v float64) {
 		return
 	}
 
-	atomicUpdateFloat(&c.valBits, func(oldVal float64) float64 {
-		return oldVal + v
-	})
+	for {
+		oldBits := atomic.LoadUint64(&c.valBits)
+		newBits := math.Float64bits(math.Float64frombits(oldBits) + v)
+		if atomic.CompareAndSwapUint64(&c.valBits, oldBits, newBits) {
+			return
+		}
+	}
 }
 
 func (c *counter) AddWithExemplar(v float64, e Labels) {

diff --git a/prometheus/gauge.go b/prometheus/gauge.go
@@ -120,9 +120,13 @@ func (g *gauge) Dec() {
 }
 
 func (g *gauge) Add(val float64) {
-	atomicUpdateFloat(&g.valBits, func(oldVal float64) float64 {
-		return oldVal + val
-	})
+	for {
+		oldBits := atomic.LoadUint64(&g.valBits)
+		newBits := math.Float64bits(math.Float64frombits(oldBits) + val)
+		if atomic.CompareAndSwapUint64(&g.valBits, oldBits, newBits) {
+			return
+		}
+	}
 }
 
 func (g *gauge) Sub(val float64) {

diff --git a/prometheus/histogram.go b/prometheus/histogram.go
@@ -1647,9 +1647,13 @@ func waitForCooldown(count uint64, counts *histogramCounts) {
 // atomicAddFloat adds the provided float atomically to another float
 // represented by the bit pattern the bits pointer is pointing to.
 func atomicAddFloat(bits *uint64, v float64) {
-	atomicUpdateFloat(bits, func(oldVal float64) float64 {
-		return oldVal + v
-	})
+	for {
+		loadedBits := atomic.LoadUint64(bits)
+		newBits := math.Float64bits(math.Float64frombits(loadedBits) + v)
+		if atomic.CompareAndSwapUint64(bits, loadedBits, newBits) {
+			break
+		}
+	}
 }
 
 // atomicDecUint32 atomically decrements the uint32 p points to.  See

diff --git a/prometheus/summary.go b/prometheus/summary.go
@@ -471,9 +471,13 @@ func (s *noObjectivesSummary) Observe(v float64) {
 	n := atomic.AddUint64(&s.countAndHotIdx, 1)
 	hotCounts := s.counts[n>>63]
 
-	atomicUpdateFloat(&hotCounts.sumBits, func(oldVal float64) float64 {
-		return oldVal + v
-	})
+	for {
+		oldBits := atomic.LoadUint64(&hotCounts.sumBits)
+		newBits := math.Float64bits(math.Float64frombits(oldBits) + v)
+		if atomic.CompareAndSwapUint64(&hotCounts.sumBits, oldBits, newBits) {
+			break
+		}
+	}
 	// Increment count last as we take it as a signal that the observation
 	// is complete.
 	atomic.AddUint64(&hotCounts.count, 1)
@@ -515,13 +519,14 @@ func (s *noObjectivesSummary) Write(out *dto.Metric) error {
 	// Finally add all the cold counts to the new hot counts and reset the cold counts.
 	atomic.AddUint64(&hotCounts.count, count)
 	atomic.StoreUint64(&coldCounts.count, 0)
-
-	// Use atomicUpdateFloat to update hotCounts.sumBits atomically.
-	atomicUpdateFloat(&hotCounts.sumBits, func(oldVal float64) float64 {
-		return oldVal + sum.GetSampleSum()
-	})
-	atomic.StoreUint64(&coldCounts.sumBits, 0)
-
+	for {
+		oldBits := atomic.LoadUint64(&hotCounts.sumBits)
+		newBits := math.Float64bits(math.Float64frombits(oldBits) + sum.GetSampleSum())
+		if atomic.CompareAndSwapUint64(&hotCounts.sumBits, oldBits, newBits) {
+			atomic.StoreUint64(&coldCounts.sumBits, 0)
+			break
+		}
+	}
 	return nil
 }