fix potential hung in generate proposals, test=develop

paddle/fluid/operators/detection/generate_proposals_op.cu

@@ -286,7 +286,8 @@ static void NMS(const platform::CUDADeviceContext &ctx, const Tensor &proposals,
   }
   int *keep = keep_out->mutable_data<int>({num_to_keep}, ctx.GetPlace());
   memory::Copy(place, keep, platform::CPUPlace(), keep_vec.data(),
-               sizeof(int) * num_to_keep, 0);
+               sizeof(int) * num_to_keep, ctx.stream());
+  ctx.Wait();
 }
 
 template <typename T>
@@ -329,7 +330,8 @@ static std::pair<Tensor, Tensor> ProposalForOneImage(
   int keep_num;
   const auto gpu_place = boost::get<platform::CUDAPlace>(ctx.GetPlace());
   memory::Copy(platform::CPUPlace(), &keep_num, gpu_place,
-               keep_num_t.data<int>(), sizeof(int), 0);
+               keep_num_t.data<int>(), sizeof(int), ctx.stream());
+  ctx.Wait();
   keep_index.Resize({keep_num});
 
   Tensor scores_filter, proposals_filter;
@@ -438,9 +440,12 @@ class CUDAGenerateProposalsKernel : public framework::OpKernel<T> {
       Tensor &scores = box_score_pair.second;
 
       memory::Copy(place, rpn_rois_data + num_proposals * 4, place,
-                   proposals.data<T>(), sizeof(T) * proposals.numel(), 0);
+                   proposals.data<T>(), sizeof(T) * proposals.numel(),
+                   dev_ctx.stream());
       memory::Copy(place, rpn_roi_probs_data + num_proposals, place,
-                   scores.data<T>(), sizeof(T) * scores.numel(), 0);
+                   scores.data<T>(), sizeof(T) * scores.numel(),
+                   dev_ctx.stream());
+      dev_ctx.Wait();
       num_proposals += proposals.dims()[0];
       offset.emplace_back(num_proposals);
     }