feat(gpu): add function to check if a cuda device is available

backends/tfhe-cuda-backend/cuda/include/device.h

@@ -42,6 +42,8 @@ void cuda_destroy_stream(cudaStream_t stream, uint32_t gpu_index);
 
 void cuda_synchronize_stream(cudaStream_t stream, uint32_t gpu_index);
 
+uint32_t cuda_is_available();
+
 void *cuda_malloc(uint64_t size, uint32_t gpu_index);
 
 void *cuda_malloc_async(uint64_t size, cudaStream_t stream, uint32_t gpu_index);

backends/tfhe-cuda-backend/cuda/src/device.cu

@@ -45,6 +45,9 @@ void cuda_synchronize_stream(cudaStream_t stream, uint32_t gpu_index) {
   check_cuda_error(cudaStreamSynchronize(stream));
 }
 
+// Determine if a CUDA device is available at runtime
+uint32_t cuda_is_available() { return cudaSetDevice(0) == cudaSuccess; }
+
 /// Unsafe function that will try to allocate even if gpu_index is invalid
 /// or if there's not enough memory. A safe wrapper around it must call
 /// cuda_check_valid_malloc() first

backends/tfhe-cuda-backend/src/cuda_bind.rs

@@ -9,6 +9,8 @@ extern "C" {
 
     pub fn cuda_synchronize_stream(stream: *mut c_void, gpu_index: u32);
 
+    pub fn cuda_is_available() -> u32;
+
     pub fn cuda_malloc(size: u64, gpu_index: u32) -> *mut c_void;
 
     pub fn cuda_malloc_async(size: u64, stream: *mut c_void, gpu_index: u32) -> *mut c_void;

tfhe/src/core_crypto/gpu/mod.rs

@@ -678,6 +678,12 @@ pub fn synchronize_devices(gpu_count: u32) {
     }
 }
 
+// Determine if a cuda device is available, at runtime
+pub fn is_cuda_available() -> bool {
+    let result = unsafe { cuda_is_available() };
+    result == 1u32
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;