[core] expmap performance improvement (#1626)

* performance improvement of update_timestamp for large maps (tested with > 25 k entries)
* monitoring_get_topics sample slightly improved to allow time updates of internal (large) expmaps in case of subsequent readings

ecal/core/src/ecal_expmap.h

@@ -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.
@@ -228,27 +228,28 @@ namespace eCAL
       // Remove all elements from the cache 
       void clear()
       {
-        // Assert method is never called when cache is empty 
-        //assert(!_key_tracker.empty());
-        auto it(_key_tracker.begin());
-
-        while (it != _key_tracker.end())
-        {
-          _key_to_value.erase(it->second); // erase the element from the map 
-          it = _key_tracker.erase(it);     // erase the element from the list
-        }
-      };
+        _key_to_value.clear(); // erase all elements from the map 
+        _key_tracker.clear();  // erase all elements from the list
+      }
 
     private:
 
       // Maybe pass the iterator instead of the key? or at least only get k once
       void update_timestamp(const Key& k)
       {
-        _key_tracker.erase(_key_to_value.at(k).second);
-        auto new_iterator = _key_tracker.emplace(_key_tracker.end(), std::make_pair(get_curr_time(), k));
-        _key_to_value.at(k).second = new_iterator;
-      }
+        auto it_in_map = _key_to_value.find(k);
+        if (it_in_map != _key_to_value.end())
+        {
+          auto& it_in_list = it_in_map->second.second;
 
+          // move the element to the end of the list
+          _key_tracker.splice(_key_tracker.end(), _key_tracker, it_in_list);
+
+          // update the timestamp
+          it_in_list->first = get_curr_time();
+        }
+      }
+
       // Record a fresh key-value pair in the cache 
       std::pair<typename key_to_value_type::iterator, bool> insert(const Key& k, const T& v)
       {

samples/cpp/monitoring/monitoring_get_topics/src/monitoring_get_topics.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.
@@ -23,10 +23,11 @@
 #include <iostream>
 #include <string>
 #include <unordered_map>
+#include <thread>
 
 int main(int argc, char **argv)
 {
-  int                                   run(0), runs(1000);
+  int                                   run(0), runs(10);
   std::chrono::steady_clock::time_point start_time;
 
   // initialize eCAL core API
@@ -48,8 +49,8 @@ int main(int argc, char **argv)
       auto num_topics = topic_info_map.size();
       auto diff_time = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - start_time);
       std::cout << "GetTopics      : " << static_cast<double>(diff_time.count()) / runs << " ms" << " (" << num_topics << " topics)" << std::endl;
-      std::cout << std::endl;
     }
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
 
     // GetTopicNames
     {
@@ -66,6 +67,7 @@ int main(int argc, char **argv)
       std::cout << "GetTopicsNames : " << static_cast<double>(diff_time.count()) / runs << " ms" << " (" << num_topics << " topics)" << std::endl;
       std::cout << std::endl;
     }
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
   }
 
   // finalize eCAL API