1 files changed, 53 insertions, 0 deletions
diff --git a/share.go b/share.go
new file mode 100644
index 0000000..36b903b
--- /dev/null
+++ b/share.go
@@ -0,0 +1,53 @@
+package gui
+
+// sharedVal 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.
+//
+// A sharedVal should be closed after use.
+type sharedVal[T any] struct {
+	request chan<- chan T
+	set     chan<- T
+}
+
+func newSharedVal[T any]() sharedVal[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 sharedVal[T]{request, set}
+}
+
+// get makes a synchronous request and returns the stored value.
+func (sv sharedVal[T]) get() T {
+	c := make(chan T)
+	defer close(c)
+	sv.request <- c
+	return <-c
+}
+
+func (sv sharedVal[T]) close() {
+	close(sv.request)
+	close(sv.set)
+}