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// Package chans contains functions for manipulating channels.
package chans
import (
"context"
"reflect"
"github.com/bradenaw/juniper/xslices"
)
// SendContext sends item on channel c and returns nil, unless ctx expires in which case it returns
// ctx.Err().
func SendContext[T any](ctx context.Context, c chan<- T, item T) error {
select {
case <-ctx.Done():
return ctx.Err()
case c <- item:
return nil
}
}
// RecvContext attempts to receive from channel c. If c is closed before or during, returns (_,
// false, nil). If ctx expires before or during, returns (_, _, ctx.Err()).
func RecvContext[T any](ctx context.Context, c <-chan T) (T, bool, error) {
select {
case <-ctx.Done():
var zero T
return zero, false, ctx.Err()
case item, ok := <-c:
return item, ok, nil
}
}
// Merge sends all values from all in channels to out.
//
// Merge blocks until all ins have closed and all values have been sent. It does not close out.
func Merge[T any](out chan<- T, in ...<-chan T) {
if len(in) == 1 {
for item := range in[0] {
out <- item
}
return
} else if len(in) == 2 {
merge2(out, in[0], in[1])
return
} else if len(in) == 3 {
merge3(out, in[0], in[1], in[2])
return
}
selectCases := xslices.Map(in, func(x <-chan T) reflect.SelectCase {
return reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(x),
}
})
for {
if len(selectCases) == 0 {
return
}
chosen, item, ok := reflect.Select(selectCases)
if ok {
out <- item.Interface().(T)
} else {
selectCases = xslices.RemoveUnordered(selectCases, chosen, 1)
}
}
}
// Merge special-case with no reflection.
func merge2[T any](out chan<- T, in0, in1 <-chan T) {
nDone := 0
for {
select {
case item, ok := <-in0:
if ok {
out <- item
} else {
in0 = nil
nDone++
if nDone == 2 {
return
}
}
case item, ok := <-in1:
if ok {
out <- item
} else {
in1 = nil
nDone++
if nDone == 2 {
return
}
}
}
}
}
// Merge special-case with no reflection.
func merge3[T any](out chan<- T, in0, in1, in2 <-chan T) {
nDone := 0
for {
select {
case item, ok := <-in0:
if ok {
out <- item
} else {
in0 = nil
nDone++
if nDone == 3 {
return
}
}
case item, ok := <-in1:
if ok {
out <- item
} else {
in1 = nil
nDone++
if nDone == 3 {
return
}
}
case item, ok := <-in2:
if ok {
out <- item
} else {
in2 = nil
nDone++
if nDone == 3 {
return
}
}
}
}
}
// Replicate sends all values sent to src to every channel in dsts.
//
// Replicate blocks until src is closed and all values have been sent to all dsts. It does not close
// dsts.
func Replicate[T any](src <-chan T, dsts ...chan<- T) {
for item := range src {
for _, dst := range dsts {
dst <- item
}
}
}
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