51 lines
1.5 KiB
Go
51 lines
1.5 KiB
Go
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// Copyright 2014 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package prometheus
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import (
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"math"
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"sync/atomic"
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"time"
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)
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// atomicUpdateFloat atomically updates the float64 value pointed to by bits
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// using the provided updateFunc, with an exponential backoff on contention.
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func atomicUpdateFloat(bits *uint64, updateFunc func(float64) float64) {
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const (
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// both numbers are derived from empirical observations
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// documented in this PR: https://github.com/prometheus/client_golang/pull/1661
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maxBackoff = 320 * time.Millisecond
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initialBackoff = 10 * time.Millisecond
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)
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backoff := initialBackoff
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for {
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loadedBits := atomic.LoadUint64(bits)
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oldFloat := math.Float64frombits(loadedBits)
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newFloat := updateFunc(oldFloat)
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newBits := math.Float64bits(newFloat)
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if atomic.CompareAndSwapUint64(bits, loadedBits, newBits) {
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break
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} else {
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// Exponential backoff with sleep and cap to avoid infinite wait
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time.Sleep(backoff)
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backoff *= 2
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if backoff > maxBackoff {
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backoff = maxBackoff
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}
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}
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}
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}
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