Local and global fairness in concurrent systems

Concurrency theory suggests the use of fairness as a criterion for a reasonable execution: a transition or a process should not wait an unbounded amount of time to execute if it is enabled continuously (under weak fairness) or infinitely often (under strong fairness). Unlike multiprocessing, in actual concurrent systems one may rely on the physical nature of the system to act in a “fair” manner. However, in many realistic concurrent systems, performing the next transition may involve several smaller steps that can include negotiation and communication, and fairness can be hard to achieve. It is useful to be able to control the global fairness guaranteed by enforcing local constraints on processes. We define local fairness conditions and study their relationship with common notions of global fairness constraints.