chore(gpu): remove device synchronization in drop for CudaVec

tfhe/src/core_crypto/gpu/algorithms/glwe_sample_extraction.rs

@@ -5,16 +5,16 @@ use crate::core_crypto::gpu::{extract_lwe_samples_from_glwe_ciphertext_list_asyn
 use crate::core_crypto::prelude::{MonomialDegree, UnsignedTorus};
 use itertools::Itertools;
 
-/// For each [`GLWE Ciphertext`] (`CudaGlweCiphertextList`) given as input, extract the nth
-/// coefficient from its body as an [`LWE ciphertext`](`CudaLweCiphertextList`). This variant is
-/// GPU-accelerated.
-pub fn cuda_extract_lwe_samples_from_glwe_ciphertext_list<Scalar>(
+/// # Safety
+///
+/// - `stream` __must__ be synchronized to guarantee computation has finished, and inputs must not
+///   be dropped until stream is synchronised
+pub unsafe fn cuda_extract_lwe_samples_from_glwe_ciphertext_list_async<Scalar>(
     input_glwe_list: &CudaGlweCiphertextList<Scalar>,
     output_lwe_list: &mut CudaLweCiphertextList<Scalar>,
     vec_nth: &[MonomialDegree],
     streams: &CudaStreams,
 ) where
-    // CastInto required for PBS modulus switch which returns a usize
     Scalar: UnsignedTorus,
 {
     let in_lwe_dim = input_glwe_list
@@ -58,3 +58,25 @@ pub fn cuda_extract_lwe_samples_from_glwe_ciphertext_list<Scalar>(
         );
     }
 }
+
+/// For each [`GLWE Ciphertext`] (`CudaGlweCiphertextList`) given as input, extract the nth
+/// coefficient from its body as an [`LWE ciphertext`](`CudaLweCiphertextList`). This variant is
+/// GPU-accelerated.
+pub fn cuda_extract_lwe_samples_from_glwe_ciphertext_list<Scalar>(
+    input_glwe_list: &CudaGlweCiphertextList<Scalar>,
+    output_lwe_list: &mut CudaLweCiphertextList<Scalar>,
+    vec_nth: &[MonomialDegree],
+    streams: &CudaStreams,
+) where
+    Scalar: UnsignedTorus,
+{
+    unsafe {
+        cuda_extract_lwe_samples_from_glwe_ciphertext_list_async(
+            input_glwe_list,
+            output_lwe_list,
+            vec_nth,
+            streams,
+        );
+    }
+    streams.synchronize();
+}

tfhe/src/core_crypto/gpu/vec.rs

@@ -1,5 +1,5 @@
 use crate::core_crypto::gpu::slice::{CudaSlice, CudaSliceMut};
-use crate::core_crypto::gpu::{synchronize_device, CudaStreams};
+use crate::core_crypto::gpu::CudaStreams;
 use crate::core_crypto::prelude::Numeric;
 use std::collections::Bound::{Excluded, Included, Unbounded};
 use std::ffi::c_void;
@@ -447,8 +447,6 @@ impl<T: Numeric> Drop for CudaVec<T> {
     /// Free memory for pointer `ptr` synchronously
     fn drop(&mut self) {
         for &gpu_index in self.gpu_indexes.iter() {
-            // Synchronizes the device to be sure no stream is still using this pointer
-            synchronize_device(gpu_index);
             unsafe { cuda_drop(self.get_mut_c_ptr(gpu_index), gpu_index) };
         }
     }

tfhe/src/integer/gpu/server_key/radix/add.rs

@@ -370,6 +370,7 @@ impl CudaServerKey {
         let mut result = unsafe { ciphertexts[0].duplicate_async(streams) };
 
         if ciphertexts.len() == 1 {
+            streams.synchronize();
             return Some(result);
         }