struct DefaultDataSourceTraits

Allows overriding what type of thread-local state configuration the data

source uses. By default every data source gets independent thread-local

state, which means every instance uses separate trace writers and

incremental state even on the same thread. Some data sources (most notably

the track event data source) want to share trace writers and incremental

state on the same thread.

Allows clearing incremental state without destroying and recreating it.

This is useful for data sources that use large data structures (e.g., hash

maps) which are expensive to reallocate. Return true if clearing was

successful. If the method is not defined or returns false, the incremental

state will be destroyed and recreated.