Often true, but not exclusively so. One can sometimes create a process partitioning solution to a problem by exploiting speculative execution. You start workers which speculate the previous execution will result in their being run. If that speculation turns out to be false you discard their results, it if turned out to be true you continue with them. There was a talk at ISSCC about doing speculative branch prediction this way, two compute units where one proceeeds as if the branch isn't taken while the other proceeds as if it is, and when you finally get the result back that says which would have happened you retire the other thread, making it available for the next branch.