feat: adding NewThrottle (#396)

README.md

@@ -242,6 +242,7 @@ Concurrency helpers:
 - [AttemptWhileWithDelay](#attemptwhilewithdelay)
 - [Debounce](#debounce)
 - [DebounceBy](#debounceby)
+- [Throttle](#throttle)
 - [Synchronize](#synchronize)
 - [Async](#async)
 - [Transaction](#transaction)
@@ -2529,6 +2530,27 @@ cancel("second key")
 
 [[play](https://go.dev/play/p/d3Vpt6pxhY8)]
 
+### Throttle
+`NewThrottle` creates a throttled instance that invokes given functions only once in every interval.
+This returns 2 functions, First one is throttled function and Second one is purge function which invokes given functions immediately and reset interval timer.
+
+```go
+
+f := func() {
+	println("Called once in every 100ms")
+}
+
+throttle, purge := lo.NewThrottle(100 * time.Millisecond, f)
+
+for j := 0; j < 10; j++ {
+	throttle()
+	time.Sleep(30 * time.Millisecond)
+}
+
+purge()
+
+```
+
 ### Synchronize
 
 Wraps the underlying callback in a mutex. It receives an optional mutex.

retry.go

@@ -287,4 +287,62 @@ func (t *Transaction[T]) Process(state T) (T, error) {
 	return state, err
 }
 
-// throttle ?
+type throttle struct {
+	mu         *sync.Mutex
+	timer      *time.Timer
+	interval   time.Duration
+	callbacks  []func()
+	countLimit int
+	count      int
+}
+
+func (th *throttle) throttledFunc() {
+	th.mu.Lock()
+	defer th.mu.Unlock()
+	if th.count < th.countLimit {
+		th.count++
+
+		for _, f := range th.callbacks {
+			f()
+		}
+
+	}
+	if th.timer == nil {
+		th.timer = time.AfterFunc(th.interval, func() {
+			th.reset()
+		})
+	}
+}
+
+func (th *throttle) reset() {
+	th.mu.Lock()
+	defer th.mu.Unlock()
+
+	if th.timer != nil {
+		th.timer.Stop()
+	}
+
+	th.count = 0
+	th.timer = nil
+
+}
+
+// NewThrottle creates a throttled instance that invokes given functions only once in every interval.
+// This returns 2 functions, First one is throttled function and Second one is a function to reset interval
+func NewThrottle(interval time.Duration, f ...func()) (func(), func()) {
+	return NewThrottleWithCount(interval, 1, f...)
+}
+
+// NewThrottleWithCount is NewThrottle with count limit, throttled function will be invoked only count times in every interval.
+func NewThrottleWithCount(interval time.Duration, count int, f ...func()) (func(), func()) {
+	if count <= 0 {
+		count = 1
+	}
+	th := &throttle{
+		mu:         new(sync.Mutex),
+		interval:   interval,
+		callbacks:  f,
+		countLimit: count,
+	}
+	return th.throttledFunc, th.reset
+}

retry_test.go

@@ -498,3 +498,66 @@ func TestTransaction(t *testing.T) {
 		is.Equal(assert.AnError, err)
 	}
 }
+
+func TestNewThrottle(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+	callCount := 0
+	f1 := func() {
+		callCount++
+	}
+	th, reset := NewThrottle(10*time.Millisecond, f1)
+
+	is.Equal(0, callCount)
+	for i := 0; i < 9; i++ {
+		var wg sync.WaitGroup
+		for j := 0; j < 100; j++ {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				th()
+			}()
+		}
+		wg.Wait()
+		time.Sleep(3 * time.Millisecond)
+	}
+	// 35 ms passed
+	is.Equal(3, callCount)
+
+	// reset counter
+	reset()
+	th()
+	is.Equal(4, callCount)
+
+}
+
+func TestNewThrottleWithCount(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+	callCount := 0
+	f1 := func() {
+		callCount++
+	}
+	th, reset := NewThrottleWithCount(10*time.Millisecond, 3, f1)
+
+	// the function does not throttle for initial count number
+	for i := 0; i < 20; i++ {
+		th()
+	}
+	is.Equal(3, callCount)
+
+	time.Sleep(11 * time.Millisecond)
+
+	for i := 0; i < 20; i++ {
+		th()
+	}
+
+	is.Equal(6, callCount)
+
+	reset()
+	for i := 0; i < 20; i++ {
+		th()
+	}
+
+	is.Equal(9, callCount)
+}