fix bug of ScopeBufferedSSAGraphExecutor

test=develop

Author: chengduozh

paddle/fluid/framework/details/scope_buffered_ssa_graph_executor.cc

@@ -38,7 +38,9 @@ FeedFetchList ScopeBufferedSSAGraphExecutor::Run(
     const std::vector<std::string> &fetch_tensors) {
   if (drop_scope_counter_ == 0) {
     platform::RecordEvent e("InitLocalExeScopes");
-    PrepareLocalExeScopes();
+    if (!run_op_future_.valid()) {
+      PrepareLocalExeScopes();
+    }
     run_op_future_.get();
   }
 
@@ -77,6 +79,7 @@ void ScopeBufferedSSAGraphExecutor::DropLocalExeScopes() {
   drop_scope_event.reset(nullptr);
 
   platform::RecordEvent e("InitLocalExeScopes");
+  PrepareLocalExeScopes();
 }
 
 void ScopeBufferedSSAGraphExecutor::PrepareLocalExeScopes() {
@@ -98,7 +101,6 @@ void ScopeBufferedSSAGraphExecutor::PrepareLocalExeScopes() {
         }
       }
     }
-    return 1;
   });
 }
 

paddle/fluid/framework/details/scope_buffered_ssa_graph_executor.h

@@ -61,7 +61,7 @@ class ScopeBufferedSSAGraphExecutor : public SSAGraphExecutor {
   std::vector<Scope*> local_scopes_;
   std::vector<VariableInfo> var_infos_;
   std::vector<platform::Place> places_;
-  std::future<int> run_op_future_;
+  std::future<void> run_op_future_;
   ::ThreadPool threads_pool_;
 };
 }  // namespace details