Operating Systems: Concurrent and Distributed Software Design

11.7. Eventcounts and sequencers

The data types eventcount and sequencer have been proposed (Reed and Kanodia, 1979) as an alternative to semaphores. The operations on them are designed for any combination of concurrent execution. The notion of counts of event occurrences, increasing indefinitely from the time the system is started, is used. The fact that the 32nd and 33rd occurrences of a given event are distinguished feels better, intuitively, for a multiprocessor implementation than, for example, semaphore values 1 (event 32 occurs), 0 (handled), 1 (event 33 occurs), 0 (handled), or 1 (event 32 occurs), 2 (event 33 occurs), 1 (event 32 handled), 0 (event 33 handled). Also, the values of these counts are made available to processes through ...