clarify Reset

test=develop

paddle/fluid/framework/threadpool.cc

@@ -25,16 +25,18 @@ DEFINE_int32(dist_threadpool_size, 0,
 
 namespace paddle {
 namespace framework {
-
+std::mutex threadpool_mu;
 std::unique_ptr<ThreadPool> ThreadPool::threadpool_(nullptr);
 std::once_flag ThreadPool::init_flag_;
 
 ThreadPool* ThreadPool::GetInstance() {
+  std::lock_guard<std::mutex> l(threadpool_mu);
   std::call_once(init_flag_, &ThreadPool::Init);
   return threadpool_.get();
 }
 
-void ThreadPool::Reset() {
+void ThreadPool::TestReset() {
+  std::lock_guard<std::mutex> l(threadpool_mu);
   threadpool_.reset(nullptr);
   ThreadPool::Init();
 }

paddle/fluid/framework/threadpool.h

@@ -56,7 +56,8 @@ class ThreadPool {
   static ThreadPool* GetInstance();
 
   // delete current thread pool and create a new one.
-  static void Reset();
+  // Only used by test cases to reset the threadpool.
+  static void TestReset();
 
   ~ThreadPool();
 

paddle/fluid/framework/threadpool_test.cc

@@ -52,6 +52,6 @@ TEST(ThreadPool, ConcurrentRun) {
   for (auto& t : threads) {
     t.join();
   }
-  framework::ThreadPool::Reset();
+  framework::ThreadPool::TestReset();
   EXPECT_EQ(sum, ((n + 1) * n) / 2);
 }