set up and add sync package

1 files changed, 79 insertions, 0 deletions

diff --git a/sync/chan_fan.go b/sync/chan_fan.go
new file mode 100644
index 0000000..13957ed
--- /dev/null
+++ b/sync/chan_fan.go
@@ -0,0 +1,79 @@
+package sync
+
+import (
+	"context"
+	"sync"
+)
+
+func FanOut[T any](ctx context.Context, in <-chan T, channelCount int, buffer int) []<-chan T {
+	if in == nil {
+		// we only expect this to happen during development
+		panic("in-channel is nil")
+	}
+	if channelCount < 1 {
+		channelCount = 1
+	}
+	if buffer < 0 {
+		buffer = 0
+	}
+
+	chs := make([]chan T, channelCount)
+	for i := range channelCount {
+		chs[i] = make(chan T, buffer)
+	}
+
+	go func() {
+		defer func() {
+			for _, out := range chs {
+				close(out)
+			}
+		}()
+
+		for v := range OrDone(ctx, in) {
+			for _, out := range chs {
+				// N.b. this will block if *any* of the out channels has a full buffer
+				if !CancelOrSend(ctx, out, v) {
+					return
+				}
+			}
+		}
+	}()
+
+	outs := make([]<-chan T, channelCount)
+	for i, out := range chs {
+		outs[i] = out
+	}
+
+	return outs
+}
+
+func FanIn[T any](ctx context.Context, buffer int, ins ...<-chan T) <-chan T {
+	if buffer < 0 {
+		buffer = 0
+	}
+
+	wg := sync.WaitGroup{}
+
+	out := make(chan T, buffer)
+
+	for _, in := range ins {
+		wg.Go(func() {
+			if in == nil {
+				return
+			}
+
+			for v := range OrDone(ctx, in) {
+				if !CancelOrSend(ctx, out, v) {
+					return
+				}
+			}
+		})
+	}
+
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+
+	return out
+}