[OMON-374] Use ostringstream in Stdout backend for atomic writes (#212)

Author: awegrzyn

src/Backends/StdOut.cxx

@@ -40,7 +40,7 @@ inline unsigned long StdOut::convertTimestamp(const std::chrono::time_point<std:
     .count();
 }
 
-StdOut::StdOut(const std::string& prefix) : mStream(std::cout), mPrefix(prefix)
+StdOut::StdOut(const std::string& prefix) : mStream(), mPrefix(prefix)
 {
   setVerbosisty(Verbosity::Debug);
   MonLogger::Get() << "StdOut backend initialized" << MonLogger::End();
@@ -83,6 +83,7 @@ void StdOut::send(const Metric& metric)
     mStream << ',' << tags::TAG_KEY[key] << "=" << tags::GetValue(value);
   }
   mStream << '\n';
+  std::cout << mStream.str();
 }
 
 } // namespace backends

src/Backends/StdOut.h

@@ -18,6 +18,7 @@
 
 #include "Monitoring/Backend.h"
 #include <string>
+#include <sstream>
 
 namespace o2
 {
@@ -53,7 +54,7 @@ class StdOut final : public Backend
 
  private:
   /// Metric stream
-  std::ostream& mStream;
+  std::ostringstream mStream;
 
   /// Converts timestamp to unsigned long (miliseconds from epoch)
   /// \param timestamp    timestamp in std::chrono::time_point format

test/testThreads.cxx

@@ -0,0 +1,40 @@
+#include "../include/Monitoring/MonitoringFactory.h"
+
+#define BOOST_TEST_MODULE Test Monitoring Threads
+#define BOOST_TEST_DYN_LINK
+#include <boost/test/unit_test.hpp>
+#include <thread>
+#include <array>
+
+namespace o2
+{
+namespace monitoring
+{
+namespace Test
+{
+
+using namespace o2::monitoring;
+
+BOOST_AUTO_TEST_CASE(retrieveOtherParams)
+{
+  std::array<std::thread, 4> threads;
+  for (auto& thread : threads) {
+    thread = std::thread([] {
+      for (int i = 0; i < 20; i++) {
+        auto monitoring = MonitoringFactory::Get("stdout://");
+        monitoring->addGlobalTag("name", "Readout");
+        monitoring->addGlobalTag(tags::Key::Name, tags::Value::Readout);
+        monitoring->send({1, "myCrazyMetricI"});
+        monitoring->send({13.33, "myCrazyMetricS"});
+      }
+    });
+  }
+
+  for (auto& thread : threads) {
+    thread.join();
+  }
+}
+
+} // namespace Test
+} // namespace monitoring
+} // namespace o2