From ea601fe1f7a9f34c7c66536bf5c078f8a23a3e8e Mon Sep 17 00:00:00 2001
From: Dhanya Thattil <dhanya.thattil@psi.ch>
Date: Mon, 7 Sep 2020 11:52:51 +0200
Subject: [PATCH] lock to ensure json add header can be updated on the fly

---
 slsReceiverSoftware/src/DataStreamer.cpp | 7 ++++---
 slsReceiverSoftware/src/DataStreamer.h   | 5 +++--
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/slsReceiverSoftware/src/DataStreamer.cpp b/slsReceiverSoftware/src/DataStreamer.cpp
index 5bb21895e..74d4e37a6 100644
--- a/slsReceiverSoftware/src/DataStreamer.cpp
+++ b/slsReceiverSoftware/src/DataStreamer.cpp
@@ -69,7 +69,7 @@ void DataStreamer::SetFlippedDataX(int fd) { flippedDataX = fd; }
 
 void DataStreamer::SetAdditionalJsonHeader(
     const std::map<std::string, std::string> &json) {
-    std::lock guard<std::mutex> guard(additionalJsonMutex);
+    std::lock_guard<std::mutex> lock(additionalJsonMutex);
     additionalJsonHeader = json;
     isAdditionalJsonUpdated = true;
 }
@@ -235,10 +235,11 @@ int DataStreamer::SendHeader(sls_receiver_header *rheader, uint32_t size,
     zHeader.completeImage =
         (header.packetNumber < generalData->packetsPerFrame ? false : true);
 
+    // update local copy only if it was updated (to prevent locking each time)
     if (isAdditionalJsonUpdated) {
-        std::lock_guard<std::mutex> guard(additionalalJsonMutex);
+        std::lock_guard<std::mutex> lock(additionalJsonMutex);
         localAdditionalJsonHeader = additionalJsonHeader;
-        isAdditionalalJsonUpdated = false;
+        isAdditionalJsonUpdated = false;
     }
     zHeader.addJsonHeader = localAdditionalJsonHeader;
 
diff --git a/slsReceiverSoftware/src/DataStreamer.h b/slsReceiverSoftware/src/DataStreamer.h
index bfe9d69bd..89f213b97 100644
--- a/slsReceiverSoftware/src/DataStreamer.h
+++ b/slsReceiverSoftware/src/DataStreamer.h
@@ -16,6 +16,7 @@ class DataStreamer;
 class ZmqSocket;
 
 #include <map>
+#include <mutex>
 
 class DataStreamer : private virtual slsDetectorDefs, public ThreadObject {
 
@@ -170,10 +171,10 @@ class DataStreamer : private virtual slsDetectorDefs, public ThreadObject {
 
     /** Used by streamer thread to update local copy (reduce number of locks
      * during streaming) */
-    std::atomic<bool>{false};
+    std::atomic<bool> isAdditionalJsonUpdated{false};
 
     /** mutex to update json and to read and update local copy */
-    std::mutex additionalJsonMutex;
+    mutable std::mutex additionalJsonMutex;
 
     /** local copy of additional json header  (it can be update on the fly) */
     std::map<std::string, std::string> localAdditionalJsonHeader;