1 files changed, 32 insertions, 0 deletions
diff --git a/layout/waitgroup.go b/layout/waitgroup.go
new file mode 100644
index 0000000..e32b350
--- /dev/null
+++ b/layout/waitgroup.go
@@ -0,0 +1,32 @@
+package layout
+
+// WaitGroup is a counting semaphore used to wait for a group of goroutines to finish.
+// It differs from sync/WaitGroup in that Wait() is a channel rather than a blocking function.
+type waitgroup struct {
+	done    chan<- struct{}
+	alldone <-chan struct{}
+}
+
+// NewWaitGroup creates a group of n goroutines: a semaphore with a capacity of n.
+func newWaitGroup(n uint) waitgroup {
+	done, alldone := make(chan struct{}), make(chan struct{})
+	go func() {
+		for ; n > 0; n-- {
+			<-done
+		}
+		alldone <- *new(struct{})
+		close(done)
+		close(alldone)
+	}()
+	return waitgroup{done, alldone}
+}
+
+// Done decrements the task counter by one.
+func (wg waitgroup) Done() {
+	wg.done <- *new(struct{})
+}
+
+// Wait returns a channel that blocks until the task counter is zero.
+func (wg waitgroup) Wait() <-chan struct{} {
+	return wg.alldone
+}