Most likely it should be called single_node_exchange. single_node_default doesn't have enough context about what it's a default for (especially because reductions and exchanges are defined in the same file; single_node_exchange is defined right next to single_ndoe_reductions).
Most likely it should be called
single_node_exchange.single_node_defaultdoesn't have enough context about what it's a default for (especially because reductions and exchanges are defined in the same file;single_node_exchangeis defined right next tosingle_ndoe_reductions).