[feature] popSIFT instance counter to free resources

fixes a bug appearing after
alicevision/popsift/pull/71

Author: simogasp

src/aliceVision/feature/sift/ImageDescriber_SIFT_popSIFT.cpp

@@ -14,10 +14,13 @@
 #include <popsift/sift_octave.h>
 #include <popsift/common/device_prop.h>
 
+#include <atomic>
+
 namespace aliceVision {
 namespace feature {
 
 std::unique_ptr<PopSift> ImageDescriber_SIFT_popSIFT::_popSift = nullptr;
+std::atomic<int> ImageDescriber_SIFT_popSIFT::_instanceCounter{0};
 
 void ImageDescriber_SIFT_popSIFT::setConfigurationPreset(EImageDescriberPreset preset)
 {
@@ -95,5 +98,23 @@ void ImageDescriber_SIFT_popSIFT::resetConfiguration()
   _popSift.reset(new PopSift(config, popsift::Config::ExtractingMode, PopSift::FloatImages));
 }
 
+ImageDescriber_SIFT_popSIFT::ImageDescriber_SIFT_popSIFT(const SiftParams& params, bool isOriented)
+    : ImageDescriber()
+    , _params(params)
+    , _isOriented(isOriented)
+{
+    _instanceCounter++;
+}
+
+ImageDescriber_SIFT_popSIFT::~ImageDescriber_SIFT_popSIFT()
+{
+    _instanceCounter--;
+
+    if(_instanceCounter.load() == 0)
+    {
+        _popSift.reset(nullptr);
+    }
+}
+
 } // namespace feature
 } // namespace aliceVision

src/aliceVision/feature/sift/ImageDescriber_SIFT_popSIFT.hpp

@@ -26,11 +26,7 @@ namespace feature {
 class ImageDescriber_SIFT_popSIFT : public ImageDescriber
 {
 public:
-  ImageDescriber_SIFT_popSIFT(const SiftParams& params = SiftParams(), bool isOriented = true)
-    : ImageDescriber()
-    , _params(params)
-    , _isOriented(isOriented)
-  {}
+  explicit ImageDescriber_SIFT_popSIFT(const SiftParams& params = SiftParams(), bool isOriented = true);
 
   /**
    * @brief Check if the image describer use CUDA
@@ -109,13 +105,19 @@ class ImageDescriber_SIFT_popSIFT : public ImageDescriber
     regions.reset(new SIFT_Regions);
   }
 
+  /**
+   * @brief Destructor
+   */
+  ~ImageDescriber_SIFT_popSIFT() override;
+
 private:
 
   void resetConfiguration();
 
   SiftParams _params;
   bool _isOriented = true;
   static std::unique_ptr<PopSift> _popSift;
+  static std::atomic<int> _instanceCounter;
 };
 
 } // namespace feature