I am a former GPUprogrammer and sometimes we worry about resource contention. That scenariois when two threads access the same memory at the same time. The operatng system then serializes theprocess so all advantages to parallelizingcode are lost and who programs in parallel if not for speed up? So at that point you are back to serial processing and its slowness.
Now in several places in the Programmer's Guide they talk aboutlocks and they claim that reducers are preferred over locks because with a lock you could have two threads accessing memory that is locked. Thus slowing down the system.
This seems analogous towhat I talked about in the first paragraph. Are we atalking about the same thing here? It seems so.