Fix the error of recurrnet op in multithreading in eval process (#24357)

CreateStepScopes in recurrent op also clears scopes, which can cause segmentation fault un multi-threading. We add a lock in this PR but it may slow the computation process. We will fix in another way in next PR.

paddle/fluid/operators/recurrent_op.cc

@@ -197,7 +197,6 @@ void RecurrentOp::RunImpl(const framework::Scope &scope,
   auto &dev_ctx = *pool.Get(place);
 
   VLOG(3) << "Static RNN input sequence length = " << seq_len;
-  StepScopes scopes = CreateStepScopes(dev_ctx, scope, seq_len);
   auto reverse = Attr<bool>(kReverse);
 
   framework::Executor executor(place);
@@ -208,6 +207,13 @@ void RecurrentOp::RunImpl(const framework::Scope &scope,
       *program, block->ID(), Attr<std::vector<std::string>>(
                                  kSkipEagerDeletionVars) /*skip_ref_cnt_vars*/);
 
+  static std::mutex mutex;
+  std::lock_guard<std::mutex> lock(mutex);
+  StepScopes scopes = CreateStepScopes(dev_ctx, scope, seq_len);
+  // TODO(gfwm2013) Function CreateStepScopes would make segmentation fault in
+  // multithreading in eval process, so we use a mutex before function
+  // CreateStepScopes to make sure that the computing process is correct. This
+  // problem will fix in next pull request.
   for (size_t i = 0; i < seq_len; ++i) {
     size_t seq_offset = reverse ? seq_len - i - 1 : i;
     VLOG(3) << "Recurrent operate at the time step " << seq_offset;