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Adding Multitasking Capability to Applications Using Multiprocessing Services

   

Event Groups

An event group is essentially a group of binary semaphores. You can use event groups to indicate a number of simple events. For example, a task running on a server may need to be aware of multiple message queues. Instead of trying to poll each one in turn, the server task can wait on an event group. Whenever a message is posted on a queue, the poster can also set the bit corresponding to that queue in the event group. Doing so notifies the task, and it then knows which queue to access to extract the message. In Multiprocessing Services, an event group consists of thirty-two 1-bit flags, each of which may be set independently. When a task receives an event group, it receives all 32-bits at once (that is, it cannot poll individual bits), and all the bits in the event group are subsequently cleared.