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channel.go
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channel.go
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package lo
import (
"sync"
"time"
"github.com/samber/lo/internal/rand"
)
type DispatchingStrategy[T any] func(msg T, index uint64, channels []<-chan T) int
// ChannelDispatcher distributes messages from input channels into N child channels.
// Close events are propagated to children.
// Underlying channels can have a fixed buffer capacity or be unbuffered when cap is 0.
func ChannelDispatcher[T any](stream <-chan T, count int, channelBufferCap int, strategy DispatchingStrategy[T]) []<-chan T {
children := createChannels[T](count, channelBufferCap)
roChildren := channelsToReadOnly(children)
go func() {
// propagate channel closing to children
defer closeChannels(children)
var i uint64 = 0
for {
msg, ok := <-stream
if !ok {
return
}
destination := strategy(msg, i, roChildren) % count
children[destination] <- msg
i++
}
}()
return roChildren
}
func createChannels[T any](count int, channelBufferCap int) []chan T {
children := make([]chan T, 0, count)
for i := 0; i < count; i++ {
children = append(children, make(chan T, channelBufferCap))
}
return children
}
func channelsToReadOnly[T any](children []chan T) []<-chan T {
roChildren := make([]<-chan T, 0, len(children))
for i := range children {
roChildren = append(roChildren, children[i])
}
return roChildren
}
func closeChannels[T any](children []chan T) {
for i := 0; i < len(children); i++ {
close(children[i])
}
}
func channelIsNotFull[T any](ch <-chan T) bool {
return cap(ch) == 0 || len(ch) < cap(ch)
}
// DispatchingStrategyRoundRobin distributes messages in a rotating sequential manner.
// If the channel capacity is exceeded, the next channel will be selected and so on.
func DispatchingStrategyRoundRobin[T any](msg T, index uint64, channels []<-chan T) int {
for {
i := int(index % uint64(len(channels)))
if channelIsNotFull(channels[i]) {
return i
}
index++
time.Sleep(10 * time.Microsecond) // prevent CPU from burning 🔥
}
}
// DispatchingStrategyRandom distributes messages in a random manner.
// If the channel capacity is exceeded, another random channel will be selected and so on.
func DispatchingStrategyRandom[T any](msg T, index uint64, channels []<-chan T) int {
for {
i := rand.IntN(len(channels))
if channelIsNotFull(channels[i]) {
return i
}
time.Sleep(10 * time.Microsecond) // prevent CPU from burning 🔥
}
}
// DispatchingStrategyWeightedRandom distributes messages in a weighted manner.
// If the channel capacity is exceeded, another random channel will be selected and so on.
func DispatchingStrategyWeightedRandom[T any](weights []int) DispatchingStrategy[T] {
seq := []int{}
for i := 0; i < len(weights); i++ {
for j := 0; j < weights[i]; j++ {
seq = append(seq, i)
}
}
return func(msg T, index uint64, channels []<-chan T) int {
for {
i := seq[rand.IntN(len(seq))]
if channelIsNotFull(channels[i]) {
return i
}
time.Sleep(10 * time.Microsecond) // prevent CPU from burning 🔥
}
}
}
// DispatchingStrategyFirst distributes messages in the first non-full channel.
// If the capacity of the first channel is exceeded, the second channel will be selected and so on.
func DispatchingStrategyFirst[T any](msg T, index uint64, channels []<-chan T) int {
for {
for i := range channels {
if channelIsNotFull(channels[i]) {
return i
}
}
time.Sleep(10 * time.Microsecond) // prevent CPU from burning 🔥
}
}
// DispatchingStrategyLeast distributes messages in the emptiest channel.
func DispatchingStrategyLeast[T any](msg T, index uint64, channels []<-chan T) int {
seq := Range(len(channels))
return MinBy(seq, func(item int, min int) bool {
return len(channels[item]) < len(channels[min])
})
}
// DispatchingStrategyMost distributes messages in the fullest channel.
// If the channel capacity is exceeded, the next channel will be selected and so on.
func DispatchingStrategyMost[T any](msg T, index uint64, channels []<-chan T) int {
seq := Range(len(channels))
return MaxBy(seq, func(item int, max int) bool {
return len(channels[item]) > len(channels[max]) && channelIsNotFull(channels[item])
})
}
// SliceToChannel returns a read-only channels of collection elements.
func SliceToChannel[T any](bufferSize int, collection []T) <-chan T {
ch := make(chan T, bufferSize)
go func() {
for i := range collection {
ch <- collection[i]
}
close(ch)
}()
return ch
}
// ChannelToSlice returns a slice built from channels items. Blocks until channel closes.
func ChannelToSlice[T any](ch <-chan T) []T {
collection := []T{}
for item := range ch {
collection = append(collection, item)
}
return collection
}
// Generator implements the generator design pattern.
func Generator[T any](bufferSize int, generator func(yield func(T))) <-chan T {
ch := make(chan T, bufferSize)
go func() {
// WARNING: infinite loop
generator(func(t T) {
ch <- t
})
close(ch)
}()
return ch
}
// Buffer creates a slice of n elements from a channel. Returns the slice and the slice length.
// @TODO: we should probably provide an helper that reuse the same buffer.
func Buffer[T any](ch <-chan T, size int) (collection []T, length int, readTime time.Duration, ok bool) {
buffer := make([]T, 0, size)
index := 0
now := time.Now()
for ; index < size; index++ {
item, ok := <-ch
if !ok {
return buffer, index, time.Since(now), false
}
buffer = append(buffer, item)
}
return buffer, index, time.Since(now), true
}
// Batch creates a slice of n elements from a channel. Returns the slice and the slice length.
//
// Deprecated: Use [Buffer] instead.
func Batch[T any](ch <-chan T, size int) (collection []T, length int, readTime time.Duration, ok bool) {
return Buffer(ch, size)
}
// BufferWithTimeout creates a slice of n elements from a channel, with timeout. Returns the slice and the slice length.
// @TODO: we should probably provide an helper that reuse the same buffer.
func BufferWithTimeout[T any](ch <-chan T, size int, timeout time.Duration) (collection []T, length int, readTime time.Duration, ok bool) {
expire := time.NewTimer(timeout)
defer expire.Stop()
buffer := make([]T, 0, size)
index := 0
now := time.Now()
for ; index < size; index++ {
select {
case item, ok := <-ch:
if !ok {
return buffer, index, time.Since(now), false
}
buffer = append(buffer, item)
case <-expire.C:
return buffer, index, time.Since(now), true
}
}
return buffer, index, time.Since(now), true
}
// BatchWithTimeout creates a slice of n elements from a channel, with timeout. Returns the slice and the slice length.
//
// Deprecated: Use [BufferWithTimeout] instead.
func BatchWithTimeout[T any](ch <-chan T, size int, timeout time.Duration) (collection []T, length int, readTime time.Duration, ok bool) {
return BufferWithTimeout(ch, size, timeout)
}
// FanIn collects messages from multiple input channels into a single buffered channel.
// Output messages has no priority. When all upstream channels reach EOF, downstream channel closes.
func FanIn[T any](channelBufferCap int, upstreams ...<-chan T) <-chan T {
out := make(chan T, channelBufferCap)
var wg sync.WaitGroup
// Start an output goroutine for each input channel in upstreams.
wg.Add(len(upstreams))
for i := range upstreams {
go func(index int) {
for n := range upstreams[index] {
out <- n
}
wg.Done()
}(i)
}
// Start a goroutine to close out once all the output goroutines are done.
go func() {
wg.Wait()
close(out)
}()
return out
}
// ChannelMerge collects messages from multiple input channels into a single buffered channel.
// Output messages has no priority. When all upstream channels reach EOF, downstream channel closes.
//
// Deprecated: Use [FanIn] instead.
func ChannelMerge[T any](channelBufferCap int, upstreams ...<-chan T) <-chan T {
return FanIn(channelBufferCap, upstreams...)
}
// FanOut broadcasts all the upstream messages to multiple downstream channels.
// When upstream channel reach EOF, downstream channels close. If any downstream
// channels is full, broadcasting is paused.
func FanOut[T any](count int, channelsBufferCap int, upstream <-chan T) []<-chan T {
downstreams := createChannels[T](count, channelsBufferCap)
go func() {
for msg := range upstream {
for i := range downstreams {
downstreams[i] <- msg
}
}
// Close out once all the output goroutines are done.
for i := range downstreams {
close(downstreams[i])
}
}()
return channelsToReadOnly(downstreams)
}