|
| 1 | +package dynamicconfig |
| 2 | + |
| 3 | +import ( |
| 4 | + "math" |
| 5 | + "reflect" |
| 6 | + "sync" |
| 7 | + "time" |
| 8 | + |
| 9 | + "github.com/dgryski/go-farm" |
| 10 | + "go.temporal.io/server/common/clock" |
| 11 | +) |
| 12 | + |
| 13 | +// GradualChange represents a setting that can change its value over time in a controlled way. |
| 14 | +// The value of a GradualChange is a function of a key and the current time. Before Start, the |
| 15 | +// value is always Old for all keys, and after End it's always New. Between them, each key will |
| 16 | +// change once at a specific time (returned by When). |
| 17 | +// |
| 18 | +// A setting with type GradualChange can use ConvertGradualChange as a conversion function to |
| 19 | +// handle plain values of the underlying type as well as GradualChange structs. |
| 20 | +type GradualChange[T any] struct { |
| 21 | + Old, New T |
| 22 | + Start, End time.Time |
| 23 | +} |
| 24 | + |
| 25 | +// StaticGradualChange returns a GradualChange whose Value always returns def and whose When |
| 26 | +// always returns a time in the past. |
| 27 | +func StaticGradualChange[T any](def T) GradualChange[T] { |
| 28 | + return GradualChange[T]{New: def} |
| 29 | +} |
| 30 | + |
| 31 | +// Value returns the value for the given key at the given time. |
| 32 | +func (c *GradualChange[T]) Value(key []byte, now time.Time) T { |
| 33 | + if !now.Before(c.End) { |
| 34 | + return c.New |
| 35 | + } else if !now.After(c.Start) { |
| 36 | + return c.Old |
| 37 | + } |
| 38 | + fraction := float64(now.Sub(c.Start)) / float64(c.End.Sub(c.Start)) |
| 39 | + threshold := uint32(fraction * float64(math.MaxUint32)) |
| 40 | + if farm.Fingerprint32(key) < threshold { |
| 41 | + return c.New |
| 42 | + } |
| 43 | + return c.Old |
| 44 | +} |
| 45 | + |
| 46 | +// When returns the time when the value for key will switch from old to new. It may be the zero |
| 47 | +// time for a static GradualChange. |
| 48 | +func (c *GradualChange[T]) When(key []byte) time.Time { |
| 49 | + fraction := float64(farm.Fingerprint32(key)) / float64(math.MaxUint32) |
| 50 | + when := time.Duration(fraction * float64(c.End.Sub(c.Start))) |
| 51 | + return c.Start.Add(when) |
| 52 | +} |
| 53 | + |
| 54 | +// ConvertGradualChange is a conversion function that can handle a plain T (which represents a |
| 55 | +// static value) as well as a GradualChange[T]. It can be used to turn settings that were not |
| 56 | +// of type GradualChange into a GradualChange. |
| 57 | +// nolint:revive // cognitive-complexity // this looks complicated but each case is fairly simple |
| 58 | +func ConvertGradualChange[T any](def T) func(v any) (GradualChange[T], error) { |
| 59 | + changeConverter := ConvertStructure(StaticGradualChange(def)) |
| 60 | + |
| 61 | + // Call this once so that if it's going to panic, it panics at static init time. |
| 62 | + _, _ = changeConverter(nil) |
| 63 | + |
| 64 | + switch reflect.TypeFor[T]() { |
| 65 | + case reflect.TypeFor[bool](): |
| 66 | + return func(v any) (GradualChange[T], error) { |
| 67 | + if b, err := convertBool(v); err == nil { |
| 68 | + var change GradualChange[T] |
| 69 | + reflect.ValueOf(&change.New).Elem().SetBool(b) |
| 70 | + return change, nil |
| 71 | + } |
| 72 | + return changeConverter(v) |
| 73 | + } |
| 74 | + case reflect.TypeFor[int](): |
| 75 | + return func(v any) (GradualChange[T], error) { |
| 76 | + if i, err := convertInt(v); err == nil { |
| 77 | + var change GradualChange[T] |
| 78 | + reflect.ValueOf(&change.New).Elem().SetInt(int64(i)) |
| 79 | + return change, nil |
| 80 | + } |
| 81 | + return changeConverter(v) |
| 82 | + } |
| 83 | + case reflect.TypeFor[float64](): |
| 84 | + return func(v any) (GradualChange[T], error) { |
| 85 | + if f, err := convertFloat(v); err == nil { |
| 86 | + var change GradualChange[T] |
| 87 | + reflect.ValueOf(&change.New).Elem().SetFloat(f) |
| 88 | + return change, nil |
| 89 | + } |
| 90 | + return changeConverter(v) |
| 91 | + } |
| 92 | + case reflect.TypeFor[string](): |
| 93 | + return func(v any) (GradualChange[T], error) { |
| 94 | + if s, err := convertString(v); err == nil { |
| 95 | + var change GradualChange[T] |
| 96 | + reflect.ValueOf(&change.New).Elem().SetString(s) |
| 97 | + return change, nil |
| 98 | + } |
| 99 | + return changeConverter(v) |
| 100 | + } |
| 101 | + case reflect.TypeFor[time.Duration](): |
| 102 | + return func(v any) (GradualChange[T], error) { |
| 103 | + if d, err := convertDuration(v); err == nil { |
| 104 | + var change GradualChange[T] |
| 105 | + reflect.ValueOf(&change.New).Elem().SetInt(int64(d)) |
| 106 | + return change, nil |
| 107 | + } |
| 108 | + return changeConverter(v) |
| 109 | + } |
| 110 | + default: |
| 111 | + // nolint:forbidigo // this will be triggered from a static initializer before it can be triggered from production code |
| 112 | + panic("ConvertGradualChange can only be used with scalar types for now") |
| 113 | + } |
| 114 | +} |
| 115 | + |
| 116 | +// SubscribeGradualChange is a helper that allows subscribing to a GradualChange[T] as if it |
| 117 | +// was a T. It handles setting a timer for when the setting may change in the future. |
| 118 | +func SubscribeGradualChange[T any]( |
| 119 | + subscribable TypedSubscribable[GradualChange[T]], |
| 120 | + changeKey []byte, |
| 121 | + callback func(T), |
| 122 | + timeSource clock.TimeSource, |
| 123 | +) (T, func()) { |
| 124 | + w := &gradualChangeSubscribeWrapper[T]{changeKey: changeKey, callback: callback, clock: timeSource} |
| 125 | + |
| 126 | + w.lock.Lock() |
| 127 | + w.change, w.cancelSub = subscribable(w.changeCallback) |
| 128 | + val, _ := w.reevalLocked() |
| 129 | + w.lock.Unlock() |
| 130 | + |
| 131 | + return val, w.cancel |
| 132 | +} |
| 133 | + |
| 134 | +type gradualChangeSubscribeWrapper[T any] struct { |
| 135 | + // constant: |
| 136 | + changeKey []byte |
| 137 | + callback func(T) |
| 138 | + clock clock.TimeSource |
| 139 | + // mutable, protected by lock: |
| 140 | + lock sync.Mutex |
| 141 | + cancelSub func() |
| 142 | + change GradualChange[T] |
| 143 | + val T |
| 144 | + tmr clock.Timer |
| 145 | +} |
| 146 | + |
| 147 | +func (w *gradualChangeSubscribeWrapper[T]) changeCallback(change GradualChange[T]) { |
| 148 | + w.lock.Lock() |
| 149 | + w.change = change |
| 150 | + val, changed := w.reevalLocked() |
| 151 | + w.lock.Unlock() |
| 152 | + |
| 153 | + if changed { |
| 154 | + w.callback(val) |
| 155 | + } |
| 156 | +} |
| 157 | + |
| 158 | +func (w *gradualChangeSubscribeWrapper[T]) timerCallback() { |
| 159 | + w.lock.Lock() |
| 160 | + val, changed := w.reevalLocked() |
| 161 | + w.lock.Unlock() |
| 162 | + |
| 163 | + if changed { |
| 164 | + w.callback(val) |
| 165 | + } |
| 166 | +} |
| 167 | + |
| 168 | +func (w *gradualChangeSubscribeWrapper[T]) cancel() { |
| 169 | + w.lock.Lock() |
| 170 | + defer w.lock.Unlock() |
| 171 | + |
| 172 | + w.cancelSub() |
| 173 | + w.setTimerLocked(nil) |
| 174 | +} |
| 175 | + |
| 176 | +func (w *gradualChangeSubscribeWrapper[T]) reevalLocked() (T, bool) { |
| 177 | + now := w.clock.Now() |
| 178 | + |
| 179 | + var newTmr clock.Timer |
| 180 | + if at := w.change.When(w.changeKey); at.After(now) { |
| 181 | + newTmr = w.clock.AfterFunc(at.Sub(now), w.timerCallback) |
| 182 | + } |
| 183 | + w.setTimerLocked(newTmr) |
| 184 | + |
| 185 | + newVal := w.change.Value(w.changeKey, now) |
| 186 | + changed := !reflect.DeepEqual(w.val, newVal) |
| 187 | + w.val = newVal |
| 188 | + return w.val, changed |
| 189 | +} |
| 190 | + |
| 191 | +func (w *gradualChangeSubscribeWrapper[T]) setTimerLocked(newTmr clock.Timer) { |
| 192 | + if w.tmr != nil { |
| 193 | + w.tmr.Stop() |
| 194 | + } |
| 195 | + w.tmr = newTmr |
| 196 | +} |
0 commit comments