Introduced a newStreamSignal() callback for Island Executables

modules/gapi/src/compiler/gislandmodel.hpp

@@ -123,6 +123,24 @@ public:
     virtual bool canReshape() const = 0;
     virtual void reshape(ade::Graph& g, const GCompileArgs& args) = 0;
 
+    // This method is called when the GStreamingCompiled gets a new
+    // input source to process. Normally this method is called once
+    // per stream execution.
+    //
+    // The idea of this method is to reset backend's stream-associated
+    // internal state, if there is any.
+    //
+    // The regular GCompiled invocation doesn't call this, there may
+    // be reset() introduced there but it is completely unnecessary at
+    // this moment.
+    //
+    // FIXME: The design on this and so-called "stateful" kernels is not
+    // closed yet.
+    // FIXME: This thing will likely break stuff once we introduce
+    // "multi-source streaming", a better design needs to be proposed
+    // at that stage.
+    virtual void handleNewStream() {}; // do nothing here by default
+
     virtual ~GIslandExecutable() = default;
 };
 

modules/gapi/src/executor/gstreamingexecutor.cpp

@@ -859,6 +859,7 @@ void cv::gimpl::GStreamingExecutor::setSource(GRunArgs &&ins)
         for (auto &&out_eh : op.nh->outNodes()) {
             out_queues.push_back(reader_queues(*m_island_graph, out_eh));
         }
+        op.isl_exec->handleNewStream();
 
         m_threads.emplace_back(islandActorThread,
                                op.in_objects,