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Concurrency

Process concurrency is expressed using the Fork and Join shapes. As the names suggest, the Fork shape allows control to pass concurrently to multiple outgoing flows, and the Join shape is used to synchronize the resulting outgoing flows. The Join shape also may be used with the Decision shape to synchronize flows following the possible outcomes of a decision (refer to Figure 9.5).

At a Fork, the flow control can split at most 64 ways. The resulting flow can terminate either at an End shape or at a Join. All flows being synchronized at a Join must have emanated from a single Fork—that is, the Fork and Join shapes must be pair matched—except when Join is used with a Decision shape. As with Fork, Join too can synchronize at most 64 flows. ...