PATH Mac OS 8 Developer Documentation
> Operating System Services
> Multiprocessing Services
>
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Adding Multitasking Capability to Applications Using Multiprocessing Services
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PATHMac OS 8 Developer Documentation
> Operating System Services
> Multiprocessing Services
>
|
|
Adding Multitasking Capability to Applications Using Multiprocessing Services
|
A message queue is a collection of data (messages) that must be processed by tasks in a first-in, first-out order. Several tasks can wait on a single queue, but only one will obtain any particular message. Messages are useful for telling a task what work to do and where to look for information relevant to the request being made. They are also useful for indicating that a given request has been processed and, if necessary, what the results are.
Typically a task has two message queues, one for input and one for output. You can think of message queues as In boxes and Out boxes. For example, your In box at work may contain a number of papers (messages) indicating work to do. After completing a job, you would place another message in the Out box. Note that if you have more than one person assigned to an In box/Out box pair, each person can work independently, allowing data to be processed in parallel.
In Multiprocessing Services, a message is 96-bits of data that can convey any desired information.
Message queues incur more overhead than the other two notification mechanisms. If you must synchronize frequently, you should try to use semaphores instead of message queues whenever possible.