[Yt-dev] possible bug in mpi get_data

[John Wise]

Hi,

I think I found a little bug when calling get_data() in parallel jobs.  I was trying to make basic slices of Density, Temperature, and Electron_Fraction.  When it gets to the Electron_Fraction slice, it already had the data in memory, so temp_data == {}.  I'm not sure why it was already in memory, I hadn't accessed Electron_Density yet.  Perhaps it was loaded from the .yt file?  Then the routine tries to accumulate temp_data with _mpi_catdict(), and this is where things go wrong because temp_data is empty!

An if-statement before this call avoided this bug,

diff -r c248cd4313a8 yt/lagos/BaseDataTypes.py
--- a/yt/lagos/BaseDataTypes.py Sun Mar 28 23:31:52 2010 -0700
+++ b/yt/lagos/BaseDataTypes.py Mon Mar 29 12:47:20 2010 -0400
@@ -593,7 +593,8 @@
             # Now the next field can use this field
             self[field] = temp_data[field]
         # We finalize
-        temp_data = self._mpi_catdict(temp_data)
+        if temp_data != {}:
+            temp_data = self._mpi_catdict(temp_data)
         # And set, for the next group
         for field in temp_data.keys():
             self[field] = temp_data[field]

I just wanted to make sure that this is the right thing to do before committing.

John