Fix bugs with hanging frames

modules/gapi/src/backends/ie/giebackend.cpp

@@ -630,6 +630,11 @@ void cv::gimpl::ie::RequestPool::callback(cv::gimpl::ie::RequestPool::Task task,
                                           InferenceEngine::InferRequest& request,
                                           size_t id) {
     task.callback(request);
+    // NB: IE::InferRequest keeps the callback until the new one is set.
+    // Since user's callback might keep resources that should be released,
+    // need to destroy its after execution.
+    // Let's set the empty one to cause the destruction of a callback.
+    request.SetCompletionCallback([](){});
     m_idle_ids.push(id);
 }
 
@@ -831,7 +836,6 @@ static void PostOutputs(InferenceEngine::InferRequest   &request,
         auto output = ctx->output(i);
         ctx->out.meta(output, ctx->input(0).meta);
         ctx->out.post(std::move(output));
-
     }
 }
 

modules/gapi/src/executor/gstreamingexecutor.cpp

@@ -347,6 +347,10 @@ bool QueueReader::getInputVector(std::vector<Q*> &in_queues,
                                  cv::GRunArgs    &in_constants,
                                  cv::GRunArgs    &isl_inputs)
 {
+    // NB: Need to release resources from the previous step, to fetch new ones.
+    // On some systems it might be impossible to allocate new memory
+    // until the old one is released.
+    m_cmd.clear();
     // NOTE: in order to maintain the GRunArg's underlying object
     // lifetime, keep the whole cmd vector (of size == # of inputs)
     // in memory.