speedbar-stealthy-function-list

speedbar-stealthy-function-list is a variable defined in `speedbar.el'.
Its value is

(("vhdl directory" vhdl-speedbar-update-current-unit)
 ("vhdl project" vhdl-speedbar-update-current-project vhdl-speedbar-update-current-unit)
 ("files" speedbar-update-current-file speedbar-check-read-only speedbar-check-vc speedbar-check-objects))

Documentation:
List of functions to periodically call stealthily.
This list is of the form:
'( ("NAME" FUNCTION ...)
...)
where NAME is the name of the major display mode these functions are
for, and the remaining elements FUNCTION are functions to call in order.
Each function must return nil if interrupted, or t if completed.
Stealthy functions which have a single operation should always return t.
Functions which take a long time should maintain a state (where they
are in their speedbar related calculations) and permit interruption.
See `speedbar-check-vc' as a good example.