Make a "build queue" for star port.
IMO, current "build same ship until manually canceled" policy is ineffective, tiresome and counterproductive, etc, etc... (This option can be turned off, but then you have to manually set the planet to build new ship after previous has been completed (which is even more ineffective, tiresome, boring, counterproductive, etc, etc, ...))
After all ships from the queue have been built stop production.
Example. I wish to build 10 constructors and have 3 production specialized planets.
(currently) Since I have no control on how many ships will be built per planet I can end up with god knows how many (since every planet takes different number of turns to complete each it gets very hard to produce exactly 10).
(with queuing) I assign 2 planets to build 3 constructors, and one planet 4. Problem solved.