From 0411d191b864035b4e214cbd9388dcf7caf9ea1a Mon Sep 17 00:00:00 2001
From: Rob Fisher <rob.fisher@hbkworld.com>
Date: Thu, 27 Aug 2026 14:25:03 +0000
Subject: [PATCH 1/2] Only rescan the subtree that changed

Rescanning from the root while openDAQ holds the changed component's lock
deadlocks against anything holding another device's lock.
---
 .../websocket_streaming/ws_streaming_server.h |  2 ++
 .../src/ws_streaming_server.cpp               | 32 +++++++++++++++----
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/shared/libraries/websocket_streaming/include/websocket_streaming/ws_streaming_server.h b/shared/libraries/websocket_streaming/include/websocket_streaming/ws_streaming_server.h
index 11c0f72..339ada2 100644
--- a/shared/libraries/websocket_streaming/include/websocket_streaming/ws_streaming_server.h
+++ b/shared/libraries/websocket_streaming/include/websocket_streaming/ws_streaming_server.h
@@ -106,6 +106,8 @@ class WsStreamingServer : public Server
             CoreEventArgsPtr& args);
 
         void rescan();
+        void rescan(FolderPtr folder);
+        void pruneRemovedSignals();
 
     private:
 
diff --git a/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp b/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp
index f9c36ac..76c910a 100644
--- a/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp
+++ b/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp
@@ -194,6 +194,10 @@ void WsStreamingServer::addCapability()
 
 void WsStreamingServer::createListener(const SignalPtr& signal)
 {
+    // Without a descriptor there is no way to know which kind of handler to create.
+    if (!signal.getDescriptor().assigned())
+        return;
+
     SignalPtr domainSignal = signal.getDomainSignal();
 
     if (domainSignal.assigned())
@@ -313,31 +317,36 @@ void WsStreamingServer::onComponentAdded(
     ComponentPtr& component,
     CoreEventArgsPtr& args)
 {
-    rescan();
+    // openDAQ holds the changed component's lock while core event handlers run, so scanning
+    // from the root here deadlocks against a thread holding any other device's lock.
+    if (auto folder = component.asPtrOrNull<daq::IFolder>(); folder.assigned())
+        rescan(folder);
 }
 
 void WsStreamingServer::onComponentRemoved(
     ComponentPtr& component,
     CoreEventArgsPtr& args)
 {
-    rescan();
+    pruneRemovedSignals();
 }
 
 void WsStreamingServer::onComponentUpdateEnd(
     ComponentPtr& component,
     CoreEventArgsPtr& args)
 {
-    rescan();
+    if (auto signal = component.asPtrOrNull<daq::ISignal>(); signal.assigned())
+        createListener(signal);
 }
 
 void WsStreamingServer::onAttributeChanged(
     ComponentPtr& component,
     CoreEventArgsPtr& args)
 {
-    rescan();
+    if (auto signal = component.asPtrOrNull<daq::ISignal>(); signal.assigned())
+        createListener(signal);
 }
 
-void WsStreamingServer::rescan()
+void WsStreamingServer::pruneRemovedSignals()
 {
     auto it = _localSignals.begin();
     while (it != _localSignals.end())
@@ -352,10 +361,19 @@ void WsStreamingServer::rescan()
         else
             ++it;
     }
+}
+
+void WsStreamingServer::rescan()
+{
+    pruneRemovedSignals();
+    rescan(_rootDevice);
+}
 
-    auto items = _rootDevice.getItems(search::Recursive(search::Any()));
+void WsStreamingServer::rescan(FolderPtr folder)
+{
+    auto items = folder.getItems(search::Recursive(search::Any()));
     for (const auto& item : items)
-        if (auto signal = item.asPtrOrNull<daq::ISignal>(); signal.assigned() && signal.getDescriptor().assigned())
+        if (auto signal = item.asPtrOrNull<daq::ISignal>(); signal.assigned())
             createListener(signal);
 }
 

From 2b4fc87a0dc71cc7cbfad0ba7648ec29e59fcb60 Mon Sep 17 00:00:00 2001
From: Rob Fisher <rob.fisher@hbkworld.com>
Date: Wed, 23 Sep 2026 11:37:16 +0000
Subject: [PATCH 2/2] Addresses comment left by copilot

---
 .../websocket_streaming/src/ws_streaming_server.cpp  | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp b/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp
index 76c910a..8340edc 100644
--- a/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp
+++ b/shared/libraries/websocket_streaming/src/ws_streaming_server.cpp
@@ -319,6 +319,7 @@ void WsStreamingServer::onComponentAdded(
 {
     // openDAQ holds the changed component's lock while core event handlers run, so scanning
     // from the root here deadlocks against a thread holding any other device's lock.
+    // The sender is the parent the component was added to, so its subtree covers the new child.
     if (auto folder = component.asPtrOrNull<daq::IFolder>(); folder.assigned())
         rescan(folder);
 }
@@ -334,7 +335,16 @@ void WsStreamingServer::onComponentUpdateEnd(
     ComponentPtr& component,
     CoreEventArgsPtr& args)
 {
-    if (auto signal = component.asPtrOrNull<daq::ISignal>(); signal.assigned())
+    // Core events are muted for the whole subtree while it updates, so this is the only
+    // notification that anything below the component changed. An update both adds and
+    // removes signals.
+    if (auto folder = component.asPtrOrNull<daq::IFolder>(); folder.assigned())
+    {
+        pruneRemovedSignals();
+        rescan(folder);
+    }
+
+    else if (auto signal = component.asPtrOrNull<daq::ISignal>(); signal.assigned())
         createListener(signal);
 }