Have a look at the Examples BATCH_WAIT and BATCH_SKIP.
Those are doing exactly what you want.
The BATCH_WAIT waits with its jobs until the previous one has finished.
The BATCH_SKIP just skips and is doing nothing if the prevois one isn't final yet.
Both are using a synchronizing resource in their top folders to lock them exclusivle with sticky mode.
BATCH_WAIT waits and BATCH_SKIP times out and skips.