[cscore] Add support for USB cameras on macOS (#4846)

The main restriction is there must be an event loop running on the main thread.
No special action is required for GUI applications, but for non-GUI applications, a
RunOsxRunLoop() function is provided that needs to be called from the main thread.

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

@@ -50,6 +50,7 @@ class SourceImpl : public PropertyContainer {
 
   void SetConnectionStrategy(CS_ConnectionStrategy strategy) {
     m_strategy = static_cast<int>(strategy);
+    NumSinksChanged();
   }
   bool IsEnabled() const {
     return m_strategy == CS_CONNECTION_KEEP_OPEN ||

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

@@ -154,7 +154,7 @@ template <typename T>
 inline std::span<T>
 UnlimitedHandleResource<THandle, TStruct, typeValue, TMutex>::GetAll(
     wpi::SmallVectorImpl<T>& vec) {
-  ForEach([&](THandle handle, const TStruct& data) { vec.push_back(handle); });
+  ForEach([&](THandle handle, const TStruct&) { vec.push_back(handle); });
   return vec;
 }
 

cscore/src/main/native/cpp/jni/CameraServerJNI.cpp

@@ -13,6 +13,7 @@
 #include "cscore_cpp.h"
 #include "cscore_cv.h"
 #include "cscore_raw.h"
+#include "cscore_runloop.h"
 #include "edu_wpi_first_cscore_CameraServerJNI.h"
 
 namespace cv {
@@ -2226,4 +2227,40 @@ Java_edu_wpi_first_cscore_CameraServerJNI_freeRawFrame
   delete ptr;
 }
 
+/*
+ * Class:     edu_wpi_first_cscore_CameraServerJNI
+ * Method:    runOsxRunLoop
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_cscore_CameraServerJNI_runOsxRunLoop
+  (JNIEnv*, jclass)
+{
+  cs::RunOsxRunLoop();
+}
+
+/*
+ * Class:     edu_wpi_first_cscore_CameraServerJNI
+ * Method:    runOsxRunLoopTimeout
+ * Signature: (D)I
+ */
+JNIEXPORT jint JNICALL
+Java_edu_wpi_first_cscore_CameraServerJNI_runOsxRunLoopTimeout
+  (JNIEnv*, jclass, jdouble timeoutSeconds)
+{
+  return cs::RunOsxRunLoopTimeout(timeoutSeconds);
+}
+
+/*
+ * Class:     edu_wpi_first_cscore_CameraServerJNI
+ * Method:    stopOsxMainRunLoop
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_cscore_CameraServerJNI_stopOsxMainRunLoop
+  (JNIEnv*, jclass)
+{
+  return cs::StopOsxMainRunLoop();
+}
+
 }  // extern "C"