Region (Combined Fragment)   A critical region interaction operator (signified by the value of region) defines a combined fragment where the messages contained in the operand cannot be interleaved with other messages from other lifelines enclosed in the region. It expresses that a set of traces are to be treated atomically and cannot be interrupted or affected by other traces.

Explanation

A critical region is a way of expressing a set of traces that need to be executed in isolation (atomically) without the possibility of being affected by other traces outside the region. A critical region takes precedence over any other enclosing fragments and does not allow other traces on any lifeline contained within the fragment to be executing at the same time. At a programming level this concept is used when a number of database tables or files are locked or a transaction is started and the locks are not released until the transaction has been executed.

Related Entries

Parallel (Combined Fragment)  Graphically Similar A combined fragment with an operator of parallel (par) is related to a combined fragment with an operator of critical region (region) because they are often used together. The parallel operator defines a number of operands that can be interleaved (overlapping in time) and the critical region is used to define a set of traces that must be executed atomically within the context of the lifelines that are enclosed within the fragment.