ImageBuffer::GetSlotStatus: the slot counters without scanning the buffer, for every image

JFJochReceiverFPGA and JFJochReceiverRugnuxStills read three slot counters for each image through
GetStatus, which walks every slot under the buffer mutex, lists the image numbers and sorts them. With a
buffer sized for 2 kHz (thousands of slots) that is about a core of CPU and time on the mutex every
other buffer user needs. GetSlotStatus returns only the counters; GetStatus stays for the HTTP status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HVeDQsU5a8AJUdJPgWevAK

common/ImageBuffer.cpp

@@ -324,6 +324,17 @@ size_t ImageBuffer::GetBufferSize() const {
     return buffer_size;
 }
 
+ImageBufferStatus ImageBuffer::GetSlotStatus() const {
+    ImageBufferStatus ret{};
+    std::unique_lock ul(m);
+    ret.total_slots = slot_count;
+    ret.available_slots = slot_count - slots_sending - slots_preparation;
+    ret.preparation_slots = slots_preparation;
+    ret.sending_slots = slots_sending;
+    ret.current_counter = counter;
+    return ret;
+}
+
 ImageBufferStatus ImageBuffer::GetStatus() const {
     ImageBufferStatus ret;
     {

common/ImageBuffer.h

@@ -92,5 +92,7 @@ public:
     void SaveStartMessage(const std::vector<uint8_t> &msg);
     void GetStartMessage(std::vector<uint8_t> &out_v);
 
+    // Only the slot counters, no image list: cheap enough to call for every image
+    ImageBufferStatus GetSlotStatus() const;
     ImageBufferStatus GetStatus() const;
 };

receiver/JFJochReceiverFPGA.cpp

@@ -350,7 +350,7 @@ void JFJochReceiverFPGA::FrameTransformationThread(uint32_t threadid) {
 
             analyzer->Process(message, local_spot_finding_settings);
 
-            auto status = image_buffer.GetStatus();
+            auto status = image_buffer.GetSlotStatus();
             message.receiver_buf_available = status.available_slots;
             message.receiver_buf_in_preparation = status.preparation_slots;
             message.receiver_buf_in_sending = status.sending_slots;

receiver/JFJochReceiverRugnuxStills.cpp

@@ -152,7 +152,7 @@ ZeroCopyReturnValue *JFJochReceiverRugnuxStills::AnalysedImageSlot() {
 
 void JFJochReceiverRugnuxStills::SendAnalysedImage(DataMessage &message, const AzimuthalIntegrationProfile &profile) {
     try {
-        const auto status = image_buffer.GetStatus();
+        const auto status = image_buffer.GetSlotStatus();
         message.receiver_buf_available = status.available_slots;
         message.receiver_buf_in_preparation = status.preparation_slots;
         message.receiver_buf_in_sending = status.sending_slots;

tests/ImageBufferTest.cpp

@@ -49,6 +49,10 @@ TEST_CASE("ImageBuffer") {
     REQUIRE(buf_ctrl.GetStatus().preparation_slots == 2);
     REQUIRE(buf_ctrl.GetStatus().sending_slots == 2);
     REQUIRE(buf_ctrl.GetStatus().available_slots == 0);
+    REQUIRE(buf_ctrl.GetSlotStatus().total_slots == 4);
+    REQUIRE(buf_ctrl.GetSlotStatus().preparation_slots == 2);
+    REQUIRE(buf_ctrl.GetSlotStatus().sending_slots == 2);
+    REQUIRE(buf_ctrl.GetSlotStatus().available_slots == 0);
 
     ret2->ReadyToSend();
     ret3->ReadyToSend();