use thread local instance test=develop

paddle/fluid/platform/debug_support.cc

@@ -23,8 +23,10 @@ template <>
 std::string PythonDebugSupport::Format() const {
   std::ostringstream sout;
   sout << "\nPython Callstacks: \n";
-  for (auto& line : info) {
+  if (!info.empty()) {
-    sout << line;
+    for (auto &line : info) {
+      sout << line;
+    }
   }
   return sout.str();
 }

paddle/fluid/platform/debug_support.h

@@ -30,8 +30,8 @@ class DebugSupport {
  public:
   // Returns the singleton of DebugSupport.
   static DebugSupport* GetInstance() {
-    static std::unique_ptr<DebugSupport> debugSupport_(nullptr);
+    static thread_local std::unique_ptr<DebugSupport> debugSupport_(nullptr);
-    static std::once_flag init_flag_;
+    static thread_local std::once_flag init_flag_;
 
     std::call_once(init_flag_,
                    [&]() { debugSupport_.reset(new DebugSupport<T>()); });