Merge pull request #14346 from anton-potapov:gapi_async

* Async API for GAPI

 - naive implementation as a starting point

* Fix namespace comment in header

modules/gapi/include/opencv2/gapi/gcompiled_async.hpp

@@ -0,0 +1,28 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+//
+// Copyright (C) 2019 Intel Corporation
+
+
+#ifndef OPENCV_GAPI_GCOMPILED_ASYNC_HPP
+#define OPENCV_GAPI_GCOMPILED_ASYNC_HPP
+
+#include <future>
+#include <exception>        //for std::exception_ptr
+#include <functional>       //for std::function
+#include "opencv2/gapi/garg.hpp"
+
+namespace cv {
+    //fwd declaration
+    class GCompiled;
+
+namespace gapi{
+namespace wip {
+    GAPI_EXPORTS void                async(GCompiled& gcmpld, std::function<void(std::exception_ptr)>&& callback, GRunArgs &&ins, GRunArgsP &&outs);
+    GAPI_EXPORTS std::future<void>   async(GCompiled& gcmpld, GRunArgs &&ins, GRunArgsP &&outs);
+} // namespace gapi
+} // namespace wip
+} // namespace cv
+
+#endif // OPENCV_GAPI_GCOMPILED_ASYNC_HPP

modules/gapi/include/opencv2/gapi/gcomputation_async.hpp

@@ -0,0 +1,29 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+//
+// Copyright (C) 2019 Intel Corporation
+
+#ifndef OPENCV_GAPI_GCOMPUTATION_ASYNC_HPP
+#define OPENCV_GAPI_GCOMPUTATION_ASYNC_HPP
+
+
+#include <future>
+#include <exception>                        //for std::exception_ptr
+#include <functional>                       //for std::function
+#include "opencv2/gapi/garg.hpp"            //for GRunArgs, GRunArgsP
+#include "opencv2/gapi/gcommon.hpp"         //for GCompileArgs
+
+namespace cv {
+    //fwd declaration
+    class GComputation;
+namespace gapi {
+namespace wip  {
+    GAPI_EXPORTS void                async_apply(GComputation& gcomp, std::function<void(std::exception_ptr)>&& callback, GRunArgs &&ins, GRunArgsP &&outs, GCompileArgs &&args = {});
+    GAPI_EXPORTS std::future<void>   async_apply(GComputation& gcomp, GRunArgs &&ins, GRunArgsP &&outs, GCompileArgs &&args = {});
+} // nmaepspace gapi
+} // namespace wip
+} // namespace cv
+
+
+#endif //OPENCV_GAPI_GCOMPUTATION_ASYNC_HPP