Merge pull request #4680 from ye-luo/custom-isnan

Fix error message printing issue in the safeguard exception catch

docs/developing.rst

@@ -773,6 +773,23 @@ During Jastrow optimization, any update to the parameter data managed by the sha
 the Jastrow objects. In another example, spline coefficients are managed by a shared pointer which achieves a single copy in
 memory shared by an SPOSet and all of its clones.
 
+Log and error output
+~~~~~~~~~~~~~~~~~~~~
+
+``app_log``, ``app_warning``, ``app_err`` and ``app_debug`` print out messages only on rank 0 to avoid repetitive messages from
+every MPI rank. For this reason, they are only suitable for outputing messages identical to all MPI ranks. ``app_debug`` prints only
+when ``--verbosity=debug`` command line option is used. Messages that come from only one or a few MPI ranks should use ``std::cout``
+and ``std::cerr``.
+
+If the code needs to be stopped after an unrecoverable error that happens uniformly on all the MPI ranks, a bad input for example,
+avoid using ``app_err`` together with ``Communicate::abort(msg)`` or ``APP_ABORT(msg)`` because any MPI rank other than rank 0 may
+stop the whole run before rank 0 is able to print out the error message. To secure the printout before stopping, use
+``Communicate::barrier_and_abort(msg)`` if an MPI communicator is available or throw a custom exception ``UniformCommunicateError``
+and capture it where ``Communicate::barrier_and_abort()`` can be used. Note that ``UniformCommunicateError`` can only be used for
+uniform error, improper use may cause QMCPACK hanging.
+
+In addition, avoid directly calling C function ``abort()``, ``exit()`` and ``MPI_Abort()`` for stopping the code.
+
 .. include:: input_code.txt
 
 .. _distance-tables:

src/QMCApp/qmcapp.cpp

@@ -233,13 +233,12 @@ int main(int argc, char** argv)
   }
   catch (const std::exception& e)
   {
-    app_error() << e.what() << std::endl;
+    std::cerr << e.what() << std::endl;
     APP_ABORT("Unhandled Exception");
   }
   catch (...)
   {
-    app_error() << "Exception not derived from std::exception thrown" << std::endl;
-    APP_ABORT("Unhandled Exception");
+    APP_ABORT("Unhandled Exception (not derived from std::exception)");
   }
 
   if (OHMMS::Controller->rank() == 0)