[core] add/improved IsPublished/IsSubscribed logic (5.12.x)

additional check for CSubscriber::GetPublisherCount() using the connection state of the matching subscriber to ensure that GetPublisherCount is increased only if the matching publisher is able to send data

ecal/core/src/pubsub/ecal_subgate.cpp

@@ -1,6 +1,6 @@
 /* ========================= eCAL LICENSE =================================
  *
- * Copyright (C) 2016 - 2019 Continental Corporation
+ * Copyright (C) 2016 - 2024 Continental Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -281,8 +281,12 @@ namespace eCAL
 
         iter->second->ApplyLocLayerParameter(process_id, topic_id, tlayer.type(), writer_par);
       }
-      // inform for local publisher connection
-      iter->second->ApplyLocPublication(process_id, topic_id, topic_info);
+      // we only inform the subscriber when the publisher has already recognized at least one local subscriber
+      // this should avoid to set the "IsPublished" state before the publisher is able to send data
+      if (ecal_sample_.topic().connections_loc() > 0)
+      {
+        iter->second->ApplyLocPublication(process_id, topic_id, topic_info);
+      }
     }
   }
 
@@ -331,8 +335,12 @@ namespace eCAL
         const std::string writer_par = tlayer.par_layer().SerializeAsString();
         iter->second->ApplyExtLayerParameter(host_name, tlayer.type(), writer_par);
       }
-      // inform for external publisher connection
-      iter->second->ApplyExtPublication(host_name, process_id, topic_id, topic_info);
+      // we only inform the subscriber when the publisher has already recognized at least one external subscriber
+      // this should avoid to set the "IsPublished" state before the publisher is able to send data
+      if (ecal_sample_.topic().connections_ext() > 0)
+      {
+        iter->second->ApplyExtPublication(host_name, process_id, topic_id, topic_info);
+      }
     }
   }
 

testing/ecal/pubsub_test/src/pubsub_receive_test.cpp

@@ -1,6 +1,6 @@
 /* ========================= eCAL LICENSE =================================
  *
- * Copyright (C) 2016 - 2019 Continental Corporation
+ * Copyright (C) 2016 - 2024 Continental Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -219,3 +219,97 @@ TEST(SUBSCRIBER, SporadicEmptyReceives)
   // finalize eCAL API
   EXPECT_EQ(0, eCAL::Finalize());
 }
+
+TEST(PubSub, TestSubscriberSeen)
+{
+  // initialize eCAL API
+  EXPECT_EQ(0, eCAL::Initialize(0, nullptr, "subscriber_seen"));
+
+  // enable data loopback
+  eCAL::Util::EnableLoopback(true);
+
+  std::atomic<bool> subscriber_seen_at_publication_start(false);
+  std::atomic<bool> subscriber_seen_at_publication_end(false);
+
+  std::atomic<bool> do_start_publication(false);
+  std::atomic<bool> publication_finished(false);
+
+  // publishing thread
+  auto publisher_thread = [&]() {
+    eCAL::CPublisher pub("blob");
+    pub.ShmSetAcknowledgeTimeout(500);
+
+    int cnt(0);
+    const auto max_runs(1000);
+    while (eCAL::Ok())
+    {
+      if (do_start_publication && cnt < max_runs)
+      {
+        if (cnt == 0)
+        {
+          subscriber_seen_at_publication_start = pub.IsSubscribed();
+        }
+
+        pub.Send(std::to_string(cnt));
+        cnt++;
+
+        if (cnt == max_runs)
+        {
+          subscriber_seen_at_publication_end = pub.IsSubscribed();
+          publication_finished = true;
+          break;
+        }
+      }
+    }
+    };
+
+  // subscribing thread
+  auto subscriber_thread = [&]() {
+    eCAL::CSubscriber sub("blob");
+    bool received(false);
+    auto max_lines(10);
+    auto receive_lambda = [&received, &max_lines](const char* /*topic_name_*/, const struct eCAL::SReceiveCallbackData* data_)
+      {
+        if (max_lines != 0)
+        {
+          // the final log should look like this
+          // -----------------------------------
+          //  Receiving 0
+          //  Receiving 1
+          //  Receiving 2
+          //  Receiving 3
+          //  Receiving 4
+          //  Receiving 5
+          //  Receiving 6
+          //  Receiving 7
+          //  Receiving 8
+          //  Receiving 9
+          // -----------------------------------
+          std::cout << "Receiving " << std::string(static_cast<const char*>(data_->buf), data_->size) << std::endl;
+          max_lines--;
+        }
+      };
+    sub.AddReceiveCallback(receive_lambda);
+
+    while (eCAL::Ok() && !publication_finished)
+    {
+      //if (sub.IsPublished()) do_start_publication = true;
+      if (sub.GetPublisherCount() > 0) do_start_publication = true;
+    }
+    };
+
+  // create threads for publisher and subscriber
+  std::thread pub_thread(publisher_thread);
+  std::thread sub_thread(subscriber_thread);
+
+  // join threads to the main thread
+  pub_thread.join();
+  sub_thread.join();
+
+  // finalize eCAL API
+  eCAL::Finalize();
+
+  // check if the publisher has seen the subscriber
+  EXPECT_TRUE(subscriber_seen_at_publication_start);
+  EXPECT_TRUE(subscriber_seen_at_publication_end);
+}