Fdw cleanup

Hi, Hackers,

I need some help to understand foreign table error handling.

For a query on foreign table, ExecInitForeignScan is called, which in turn
calls the BeginForeignScan hook. Inside this hook, I allocated some
resource,

node->fdw_state = allocate_resource(...);

If everything goes well, ExecEndForeignScan will call call my
EndForeignScan hook, inside the hook, I free the resource.

free_resource(node->fdw_state);

However, if during the execution an error happened, seems to me that
EndForeignScan will not be called (traced using gdb). So my question is,
is Begin/End the right place for allocate/free resources? If it is not,
what is the right way to do this?

Thank you very much,
Feng