Multiple Events

Abstract

Avoiding deadlock is the principal concern involved when working with multiple mutexes — however, this is typically less of a problem for multiple events where the prime difficulty is usually accommodating the unpredictable order in which different events may occur. There are basically two common modes of operation — either a thread can wait for one out of several events to be signalled or alternatively the thread can wait for all events in a set to become signalled simultaneously. In the latter case several threads may be waiting for some of the same events so that the various event sets overlap — to prevent holding up other threads unnecessarily a thread must only receive a signal for one of the events it is waiting for if it can do so for all such events together. The MULTI_EVENT class is designed to support both of these modes of operation — each MULTI_EVENT object manages a collection of events internally and each of these events may be referenced using a unique integer ‘cookie’ value. The key topics covered by this chapter include:

• overlapping event sets

• random event monitoring

• the MULTI_EVENT class

• implementation details for UNIX and Windows