[cscore] Add USB camera change event (#3123)

cscore/src/main/native/cpp/Instance.cpp

@@ -36,7 +36,10 @@ static void def_log_func(unsigned int level, const char* file,
   wpi::errs() << oss.str();
 }
 
-Instance::Instance() : telemetry(notifier), networkListener(logger, notifier) {
+Instance::Instance()
+    : telemetry(notifier),
+      networkListener(logger, notifier),
+      usbCameraListener(logger, notifier) {
   SetDefaultLogger();
 }
 
@@ -52,6 +55,7 @@ void Instance::Shutdown() {
   m_sinks.FreeAll();
   m_sources.FreeAll();
   networkListener.Stop();
+  usbCameraListener.Stop();
   telemetry.Stop();
   notifier.Stop();
 }

cscore/src/main/native/cpp/Instance.h

@@ -18,6 +18,7 @@
 #include "SourceImpl.h"
 #include "Telemetry.h"
 #include "UnlimitedHandleResource.h"
+#include "UsbCameraListener.h"
 
 namespace cs {
 
@@ -54,6 +55,7 @@ class Instance {
   Notifier notifier;
   Telemetry telemetry;
   NetworkListener networkListener;
+  UsbCameraListener usbCameraListener;
 
  private:
   UnlimitedHandleResource<Handle, SourceData, Handle::kSource> m_sources;

cscore/src/main/native/cpp/Notifier.cpp

@@ -94,3 +94,7 @@ void Notifier::NotifyNetworkInterfacesChanged() {
 void Notifier::NotifyTelemetryUpdated() {
   Send(UINT_MAX, RawEvent::kTelemetryUpdated);
 }
+
+void Notifier::NotifyUsbCamerasChanged() {
+  Send(UINT_MAX, RawEvent::kUsbCamerasChanged);
+}

cscore/src/main/native/cpp/Notifier.h

@@ -83,6 +83,7 @@ class Notifier : public wpi::CallbackManager<Notifier, impl::NotifierThread> {
                           const wpi::Twine& valueStr);
   void NotifyNetworkInterfacesChanged();
   void NotifyTelemetryUpdated();
+  void NotifyUsbCamerasChanged();
 };
 
 }  // namespace cs

cscore/src/main/native/cpp/UsbCameraListener.h

@@ -0,0 +1,31 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#ifndef CSCORE_USBCAMERALISTENER_H_
+#define CSCORE_USBCAMERALISTENER_H_
+
+#include <memory>
+
+#include <wpi/Logger.h>
+
+namespace cs {
+
+class Notifier;
+
+class UsbCameraListener {
+ public:
+  UsbCameraListener(wpi::Logger& logger, Notifier& notifier);
+  ~UsbCameraListener();
+
+  void Start();
+  void Stop();
+
+ private:
+  class Impl;
+  std::unique_ptr<Impl> m_impl;
+};
+
+}  // namespace cs
+
+#endif  // CSCORE_USBCAMERALISTENER_H_

cscore/src/main/native/cpp/cscore_cpp.cpp

@@ -718,6 +718,13 @@ static void StartBackground(int eventMask, bool immediateNotify) {
       inst.notifier.NotifyNetworkInterfacesChanged();
     }
   }
+  if ((eventMask & CS_USB_CAMERAS_CHANGED) != 0) {
+    // start network interface event listener
+    inst.usbCameraListener.Start();
+    if (immediateNotify) {
+      inst.notifier.NotifyUsbCamerasChanged();
+    }
+  }
 }
 
 CS_Listener AddListener(std::function<void(const RawEvent& event)> callback,