Val

1 files changed, 53 insertions, 0 deletions

diff --git a/val.go b/val.go
new file mode 100644
index 0000000..4d35fb9
--- /dev/null
+++ b/val.go
@@ -0,0 +1,53 @@
+package share
+
+// Val is a concurrent interface to a piece of shared data.
+//
+// A client can read the data by sending a channel via request, and the stored value will
+// be sent back via the channel. The client is responsible for closing the channel.
+//
+// The stored value can be changed by sending the new value via Set. Requests block until
+// the first value is received on Set.
+//
+// Val should be closed after use.
+type Val[T any] struct {
+	Request chan<- chan T
+	Set     chan<- T
+}
+
+func NewVal[T any]() Val[T] {
+	request := make(chan chan T)
+	set := make(chan T)
+	go func() {
+		val := <-set // wait for initial value
+		for {
+			select {
+			case v, ok := <-set:
+				if !ok { // closed
+					return
+				}
+				val = v
+			case req, ok := <-request:
+				if !ok { // closed
+					return
+				}
+				go func() { // don't wait for client to receive
+					req <- val
+				}()
+			}
+		}
+	}()
+	return Val[T]{request, set}
+}
+
+// Get makes a synchronous request and returns the stored value.
+func (v Val[T]) Get() T {
+	c := make(chan T)
+	defer close(c)
+	v.Request <- c
+	return <-c
+}
+
+func (v Val[T]) Close() {
+	close(v.Request)
+	close(v.Set)
+}