From db80fa03715d006f76821ae66b941c53aea301af Mon Sep 17 00:00:00 2001
From: ev-mp <ev_mp@yahoo.com>
Date: Tue, 19 May 2020 19:11:39 +0300
Subject: [PATCH] resolve dead-lock on multi-threaded notifications calls

---
 common/notifications.cpp | 23 ++++++++++++++++-------
 common/notifications.h   |  3 ++-
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/common/notifications.cpp b/common/notifications.cpp
index 485a57e847..585ac29c7e 100644
--- a/common/notifications.cpp
+++ b/common/notifications.cpp
@@ -683,11 +683,22 @@ namespace rs2
     void notifications_model::foreach_log(std::function<void(const std::string& line)> action)
     {
         std::lock_guard<std::recursive_mutex> lock(m);
-        for (auto&& l : log)
+
+        // Process only the messages that are available upon invocation
+        std::string log_entry;
+        for (size_t len = 0; len < incoming_log_queue.size(); len++)
         {
-            action(l);
+            if (incoming_log_queue.try_dequeue(&log_entry))
+                notification_logs.push_back(log_entry);
         }
 
+        // Limit the notification window
+        while (notification_logs.size() > 200)
+            notification_logs.pop_front();
+
+        for (auto&& l : notification_logs)
+            action(l);
+
         auto rc = ImGui::GetCursorPos();
         ImGui::SetCursorPos({ rc.x, rc.y + 5 });
 
@@ -698,15 +709,13 @@ namespace rs2
         }
     }
 
+    // Callback function must not include mutex
     void notifications_model::add_log(std::string line)
     {
-        std::lock_guard<std::recursive_mutex> lock(m);
         if (!line.size()) return;
-        // Limit the notification window
-        while (log.size() > 200)
-            log.pop_front();
+
         if (line[line.size() - 1] != '\n') line += "\n";
-        log.push_back(line);
+        incoming_log_queue.enqueue(std::move(line));
         new_log = true;
     }
 
diff --git a/common/notifications.h b/common/notifications.h
index 5a3e985672..ec4d09e301 100644
--- a/common/notifications.h
+++ b/common/notifications.h
@@ -195,7 +195,8 @@ namespace rs2
         std::recursive_mutex m;
         bool new_log = false;
 
-        std::deque<std::string> log;
+        single_consumer_queue<std::string> incoming_log_queue;
+        std::deque<std::string> notification_logs;
         std::shared_ptr<notification_model> selected;
         std::chrono::system_clock::time_point last_snoozed;
     };