In a previous article I discussed the parallel execution of activities in BPEL, more specifically in Oracle BPEL PM 11g (TP4). This article concluded that true parallellism hardly exists. The branches within a Flow get their chance in turns to execute their next step. Not until an activity is complete in one branch can the next branch take over and make one step. The only exception I was able to determine was the Receive activity that waits for an Asynchronous Service to call in with its results – when a branch is executing the Receive (waiting!), other branches can continue with their next step. It seemed that normal Wait operations and Synchronous calls (with nonBlockingInvoke set) should also free the lock the current branch has and allow others to run, but I could not observe that behavior in Technical Preview 4.
I hinted in that article that we can take more control over the way the activities in the parallel branches are executed. Right now it seems that when a Flow executes, the BPEL PM determines when which branch gets a chance to run, whereby it seems – though I do not know whether that is guaranteed behavior – that the branches (BPEL sequence activities) get a turn in More >