cscore: Add connection strategy to sources (#1252)

By default, sources automatically manage their connection based on whether
any sinks are connected.  This change allows the user to keep a connection
open or force it closed regardless of the number of connected sinks.

cscore/src/main/native/cpp/HttpCameraImpl.cpp

@@ -69,13 +69,12 @@ void HttpCameraImpl::StreamThreadMain() {
     // sleep between retries
     std::this_thread::sleep_for(std::chrono::milliseconds(250));
 
-    // disconnect if no one is listening
-    if (m_numSinksEnabled == 0) {
+    // disconnect if not enabled
+    if (!IsEnabled()) {
       std::unique_lock<wpi::mutex> lock(m_mutex);
       if (m_streamConn) m_streamConn->stream->close();
-      // Wait for a sink to enable
-      m_sinkEnabledCond.wait(
-          lock, [=] { return !m_active || m_numSinksEnabled != 0; });
+      // Wait for enable
+      m_sinkEnabledCond.wait(lock, [=] { return !m_active || IsEnabled(); });
       if (!m_active) return;
     }
 
@@ -185,8 +184,8 @@ void HttpCameraImpl::DeviceStream(wpi::raw_istream& is,
   int numErrors = 0;
 
   // streaming loop
-  while (m_active && !is.has_error() && m_numSinksEnabled > 0 &&
-         numErrors < 3 && !m_streamSettingsUpdated) {
+  while (m_active && !is.has_error() && IsEnabled() && numErrors < 3 &&
+         !m_streamSettingsUpdated) {
     if (!FindMultipartBoundary(is, boundary, nullptr)) break;
 
     // Read the next two characters after the boundary (normally \r\n)

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

@@ -41,6 +41,15 @@ class SourceImpl : public PropertyContainer {
   void SetDescription(const wpi::Twine& description);
   wpi::StringRef GetDescription(wpi::SmallVectorImpl<char>& buf) const;
 
+  void SetConnectionStrategy(CS_ConnectionStrategy strategy) {
+    m_strategy = static_cast<int>(strategy);
+  }
+  bool IsEnabled() const {
+    return m_strategy == CS_CONNECTION_KEEP_OPEN ||
+           (m_strategy == CS_CONNECTION_AUTO_MANAGE && m_numSinksEnabled > 0);
+  }
+
+  // User-visible connection status
   void SetConnected(bool connected);
   bool IsConnected() const { return m_connected; }
 
@@ -130,7 +139,6 @@ class SourceImpl : public PropertyContainer {
   virtual void NumSinksEnabledChanged() = 0;
 
   std::atomic_int m_numSinks{0};
-  std::atomic_int m_numSinksEnabled{0};
 
  protected:
   // Cached video modes (protected with m_mutex)
@@ -146,6 +154,9 @@ class SourceImpl : public PropertyContainer {
   std::string m_name;
   std::string m_description;
 
+  std::atomic_int m_strategy{CS_CONNECTION_AUTO_MANAGE};
+  std::atomic_int m_numSinksEnabled{0};
+
   wpi::mutex m_frameMutex;
   wpi::condition_variable m_frameCv;
 

cscore/src/main/native/cpp/UsbCameraImpl.cpp

@@ -309,10 +309,10 @@ void UsbCameraImpl::CameraThreadMain() {
       }
     }
 
-    // Turn off streaming if no one is listening, and turn it on if there is.
-    if (m_streaming && m_numSinksEnabled == 0) {
+    // Turn off streaming if not enabled, and turn it on if enabled
+    if (m_streaming && !IsEnabled()) {
       DeviceStreamOff();
-    } else if (!m_streaming && m_numSinksEnabled > 0) {
+    } else if (!m_streaming && IsEnabled()) {
       DeviceStreamOn();
     }
 

cscore/src/main/native/cpp/cscore_c.cpp

@@ -99,10 +99,20 @@ uint64_t CS_GetSourceLastFrameTime(CS_Source source, CS_Status* status) {
   return cs::GetSourceLastFrameTime(source, status);
 }
 
+void CS_SetSourceConnectionStrategy(CS_Source source,
+                                    CS_ConnectionStrategy strategy,
+                                    CS_Status* status) {
+  cs::SetSourceConnectionStrategy(source, strategy, status);
+}
+
 CS_Bool CS_IsSourceConnected(CS_Source source, CS_Status* status) {
   return cs::IsSourceConnected(source, status);
 }
 
+CS_Bool CS_IsSourceEnabled(CS_Source source, CS_Status* status) {
+  return cs::IsSourceEnabled(source, status);
+}
+
 CS_Property CS_GetSourceProperty(CS_Source source, const char* name,
                                  CS_Status* status) {
   return cs::GetSourceProperty(source, name, status);

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

@@ -222,6 +222,17 @@ uint64_t GetSourceLastFrameTime(CS_Source source, CS_Status* status) {
   return data->source->GetCurFrameTime();
 }
 
+void SetSourceConnectionStrategy(CS_Source source,
+                                 CS_ConnectionStrategy strategy,
+                                 CS_Status* status) {
+  auto data = Sources::GetInstance().Get(source);
+  if (!data) {
+    *status = CS_INVALID_HANDLE;
+    return;
+  }
+  data->source->SetConnectionStrategy(strategy);
+}
+
 bool IsSourceConnected(CS_Source source, CS_Status* status) {
   auto data = Sources::GetInstance().Get(source);
   if (!data) {
@@ -231,6 +242,15 @@ bool IsSourceConnected(CS_Source source, CS_Status* status) {
   return data->source->IsConnected();
 }
 
+bool IsSourceEnabled(CS_Source source, CS_Status* status) {
+  auto data = Sources::GetInstance().Get(source);
+  if (!data) {
+    *status = CS_INVALID_HANDLE;
+    return false;
+  }
+  return data->source->IsEnabled();
+}
+
 CS_Property GetSourceProperty(CS_Source source, const wpi::Twine& name,
                               CS_Status* status) {
   auto data = Sources::GetInstance().Get(source);

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

@@ -599,6 +599,21 @@ Java_edu_wpi_cscore_CameraServerJNI_getSourceLastFrameTime
   return val;
 }
 
+/*
+ * Class:     edu_wpi_cscore_CameraServerJNI
+ * Method:    setSourceConnectionStrategy
+ * Signature: (II)V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_cscore_CameraServerJNI_setSourceConnectionStrategy
+  (JNIEnv* env, jclass, jint source, jint strategy)
+{
+  CS_Status status = 0;
+  cs::SetSourceConnectionStrategy(
+      source, static_cast<CS_ConnectionStrategy>(strategy), &status);
+  CheckStatus(env, status);
+}
+
 /*
  * Class:     edu_wpi_cscore_CameraServerJNI
  * Method:    isSourceConnected
@@ -614,6 +629,21 @@ Java_edu_wpi_cscore_CameraServerJNI_isSourceConnected
   return val;
 }
 
+/*
+ * Class:     edu_wpi_cscore_CameraServerJNI
+ * Method:    isSourceEnabled
+ * Signature: (I)Z
+ */
+JNIEXPORT jboolean JNICALL
+Java_edu_wpi_cscore_CameraServerJNI_isSourceEnabled
+  (JNIEnv* env, jclass, jint source)
+{
+  CS_Status status = 0;
+  auto val = cs::IsSourceEnabled(source, &status);
+  CheckStatus(env, status);
+  return val;
+}
+
 /*
  * Class:     edu_wpi_cscore_CameraServerJNI
  * Method:    getSourceProperty