Fork and Join are part of UML State diagram heritage that I imported into PLD. The example below show a potential usage to take a signal, duplicate it to three threads and wait until they all are finished before you continue. Fork and Join are drawn as bars that can be horisontal or vertical – signals can go in/out on all edges in contrary to the previous connection point version. For now this is only a drawing tool I will return to these and their code/visualization later.
Is this a flow chart or a state diagram? The reality is that you can draw state-diagrams, but they will need to convert to code so it is both. This exact diagram is excellent if process 1,2 & 3 is on three separate devices involving CAN communication etc.