The parallel gateway enables you to perform multiple tasks simultaneously, allowing your process to follow several unconditional paths in parallel. When your process token reaches a parallel gateway activity, the parallel gateway will create a token for each outgoing parallel sequence flow. Your process will wait until all tokens have arrived at the parallel gateway merge activity before resuming with the rest of the activities.
You should be very careful with the parallel gateway activity because if one of the tokens that have been created by the parallel gateway doesn't arrive at the parallel gateway merge activity, then your process will freeze.
So let's see how you can use the parallel gateway in a process. Let's assume that you are implementing an order process and that at some point in your process you want to request for quotations from two different suppliers. Once you have received both quotations your process should resume (ideally pick the lowest quotation but I will not be implementing this part).
I created a BPM application with a default BPM project (named both application and project "ParallelGatewayDemo") having an empty composite.
Go to the BPM workspace, login using the weblogic user and if you followed my exact steps and you should see two tasks. Approve one of them.
Download sample application: Parallel Gateway