Extend the cms::cuda::ScopedSetDevice interface

Add a default constructor that stores the current devices, without
changing it.

Add a set() method to change the current device, without affecting the
stored value for the original device.

HeterogeneousCore/CUDAUtilities/interface/ScopedSetDevice.h

@@ -9,20 +9,32 @@ namespace cms {
   namespace cuda {
     class ScopedSetDevice {
     public:
-      explicit ScopedSetDevice(int newDevice) {
-        cudaCheck(cudaGetDevice(&prevDevice_));
-        cudaCheck(cudaSetDevice(newDevice));
+      // Store the original device, without setting a new one
+      ScopedSetDevice() {
+        cudaCheck(cudaGetDevice(&originalDevice_));
       }
 
+      // Store the original device, and set a new current device
+      explicit ScopedSetDevice(int device) : ScopedSetDevice() {
+        set(device);
+      }
+
+      // Restore the original device
       ~ScopedSetDevice() {
         // Intentionally don't check the return value to avoid
         // exceptions to be thrown. If this call fails, the process is
         // doomed anyway.
-        cudaSetDevice(prevDevice_);
+        cudaSetDevice(originalDevice_);
+      }
+
+      // Set a new current device, without changing the original device
+      // that will be restored when this object is destroyed
+      void set(int device) {
+        cudaCheck(cudaSetDevice(device));
       }
 
     private:
-      int prevDevice_;
+      int originalDevice_;
     };
   }  // namespace cuda
 }  // namespace cms