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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package rate
import (
"sync"
"time"
)
// Sometimes will perform an action occasionally. The First, Every, and
// Interval fields govern the behavior of Do, which performs the action.
// A zero Sometimes value will perform an action exactly once.
//
// # Example: logging with rate limiting
//
// var sometimes = rate.Sometimes{First: 3, Interval: 10*time.Second}
// func Spammy() {
// sometimes.Do(func() { log.Info("here I am!") })
// }
type Sometimes struct {
First int // if non-zero, the first N calls to Do will run f.
Every int // if non-zero, every Nth call to Do will run f.
Interval time.Duration // if non-zero and Interval has elapsed since f's last run, Do will run f.
mu sync.Mutex
count int // number of Do calls
last time.Time // last time f was run
}
// Do runs the function f as allowed by First, Every, and Interval.
//
// The model is a union (not intersection) of filters. The first call to Do
// always runs f. Subsequent calls to Do run f if allowed by First or Every or
// Interval.
//
// A non-zero First:N causes the first N Do(f) calls to run f.
//
// A non-zero Every:M causes every Mth Do(f) call, starting with the first, to
// run f.
//
// A non-zero Interval causes Do(f) to run f if Interval has elapsed since
// Do last ran f.
//
// Specifying multiple filters produces the union of these execution streams.
// For example, specifying both First:N and Every:M causes the first N Do(f)
// calls and every Mth Do(f) call, starting with the first, to run f. See
// Examples for more.
//
// If Do is called multiple times simultaneously, the calls will block and run
// serially. Therefore, Do is intended for lightweight operations.
//
// Because a call to Do may block until f returns, if f causes Do to be called,
// it will deadlock.
func (s *Sometimes) Do(f func()) {
s.mu.Lock()
defer s.mu.Unlock()
if s.count == 0 ||
(s.First > 0 && s.count < s.First) ||
(s.Every > 0 && s.count%s.Every == 0) ||
(s.Interval > 0 && time.Since(s.last) >= s.Interval) {
f()
s.last = time.Now()
}
s.count++
}
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