experimental: adds close notification hook (#1574)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

experimental/close_example_test.go

@@ -0,0 +1,27 @@
+package experimental_test
+
+import (
+	"context"
+
+	"github.com/tetratelabs/wazero/experimental"
+)
+
+var ctx context.Context
+
+// This shows how to implement a custom cleanup task on close.
+func Example_closeNotifier() {
+	closeCh := make(chan struct{})
+	ctx = experimental.WithCloseNotifier(
+		ctx,
+		experimental.CloseNotifyFunc(func(context.Context, uint32) { close(closeCh) }),
+	)
+
+	// ... create module, do some work. Sometime later in another goroutine:
+
+	select {
+	case <-closeCh:
+		// do some cleanup
+	default:
+		// do some more work with the module
+	}
+}