Updated after code review

python/lsst/log/logLib.i

@@ -15,22 +15,25 @@ Access to the classes from the log library
 #include "lsst/log/logInterface.h"
 %}
 
-namespace std {
-  template <class Func>
-  class function {
-  };
-}
-
-%template(VoidFunc) std::function<void()>;
-
 %{
-// warpper for callable object to track lifetime
+// Wrapper for Python callable object to make sure that we have GIL
+// when we call Python. Note that we are leaking Python callable,
+// as C++ callables may be (and actually are in our particular case) 
+// outliving Python interpreter and attempt to delete Python object
+// will result in crash.
 class callable_wrapper {
 public:
-    callable_wrapper(PyObject* callable) : _callable(callable) {}
-    void operator()() { PyObject_CallObject(_callable, nullptr); }
+    callable_wrapper(PyObject* callable) : _callable(callable) {
+        Py_XINCREF(_callable);
+    }
+    void operator()() {
+        // make sure we own GIL before doing Python call
+        auto state = PyGILState_Ensure();
+        PyObject_CallObject(_callable, nullptr);
+        PyGILState_Release(state);
+    }
 private:
-    swig::SwigPtr_PyObject _callable;
+    PyObject* _callable;
 };
 %}
 

src/Log.cc

@@ -276,13 +276,13 @@ int Log::MDCRegisterInit(std::function<void()> function) {
 
     std::lock_guard<std::mutex> lock(mdcInitMutex);
 
-    // store function for later use
-    ::mdcInitFunctions.push_back(function);
-
     // logMsg may have been called already in this thread, to make sure that
     // this function is executed in this thread call it explicitly
     function();
 
+    // store function for later use
+    ::mdcInitFunctions.push_back(std::move(function));
+
     // return arbitrary number
     return 1;
 }
@@ -359,7 +359,7 @@ bool Log::isEnabledFor(std::string const& loggername, int level) {
   */
 void Log::log(log4cxx::LoggerPtr logger,   ///< the logger
               log4cxx::LevelPtr level,     ///< message level
-              log4cxx::spi::LocationInfo const& location,
+              log4cxx::spi::LocationInfo const& location,  ///< message origin location
               char const* fmt,             ///< message format string
               ...                          ///< message arguments
              ) {
@@ -372,10 +372,11 @@ void Log::log(log4cxx::LoggerPtr logger,   ///< the logger
 
 /** Method used by LOGS_INFO and similar macros to process a log message..
   */
-void Log::logMsg(log4cxx::LoggerPtr logger,
-                 log4cxx::LevelPtr level,
-                 log4cxx::spi::LocationInfo const& location,
-                 std::string const& msg) {
+void Log::logMsg(log4cxx::LoggerPtr logger,   ///< the logger
+                 log4cxx::LevelPtr level,     ///< message level
+                 log4cxx::spi::LocationInfo const& location,  ///< message origin location
+                 std::string const& msg       ///< message string
+                 ) {
 
     // do one-time per-thread initialization
     thread_local static bool threadInit = false;