libuv: add async

c/libuv/_demo/async/async.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"github.com/goplus/llgo/c"
+	"github.com/goplus/llgo/c/libuv"
+)
+
+func ensure(b bool, msg string) {
+	if !b {
+		panic(msg)
+	}
+}
+
+func main() {
+	loop := libuv.LoopNew()
+	defer loop.Close()
+
+	a := &libuv.Async{}
+	r := loop.Async(a, func(a *libuv.Async) {
+		println("async callback")
+		a.Close(nil) // or loop.Stop()
+	})
+	ensure(r == 0, "Async failed")
+
+	go func() {
+		println("begin async task")
+		c.Usleep(100 * 1000)
+		println("send async event")
+		ensure(a.Send() == 0, "Send failed")
+	}()
+
+	loop.Run(libuv.RUN_DEFAULT)
+	println("done")
+}
+
+/*Expected Output:
+begin async task
+send async event
+async callback
+done
+*/