Merge pull request #20119 from TolyaTalamanov:at/compile-arg-for-queue-capacity

* Support queue capacity as graph compilation argument

* Fix comments to review

* Fix comments to review

* Fix comments to review

modules/gapi/include/opencv2/gapi/gcommon.hpp

@@ -195,6 +195,14 @@ private:
 
 using GCompileArgs = std::vector<GCompileArg>;
 
+inline cv::GCompileArgs& operator += (      cv::GCompileArgs &lhs,
+                                      const cv::GCompileArgs &rhs)
+{
+    lhs.reserve(lhs.size() + rhs.size());
+    lhs.insert(lhs.end(), rhs.begin(), rhs.end());
+    return lhs;
+}
+
 /**
  * @brief Wraps a list of arguments (a parameter pack) into a vector of
  *        compilation arguments (cv::GCompileArg).

modules/gapi/include/opencv2/gapi/gstreaming.hpp

@@ -371,6 +371,31 @@ protected:
 };
 /** @} */
 
+namespace gapi {
+namespace streaming {
+/**
+ * @brief Specify queue capacity for streaming execution.
+ *
+ * In the streaming mode the pipeline steps are connected with queues
+ * and this compile argument controls every queue's size.
+ */
+struct GAPI_EXPORTS queue_capacity
+{
+    explicit queue_capacity(size_t cap = 1) : capacity(cap) { };
+    size_t capacity;
+};
+/** @} */
+} // namespace streaming
+} // namespace gapi
+
+namespace detail
+{
+template<> struct CompileArgTag<cv::gapi::streaming::queue_capacity>
+{
+    static const char* tag() { return "gapi.queue_capacity"; }
+};
+}
+
 }
 
 #endif // OPENCV_GAPI_GSTREAMING_COMPILED_HPP