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T E C H N O T E :
On the Deferred
Task Manager
By Matthew Xavier Mora
Apple Developer Technical Support (DTS)
This Note highlights two points ‹ interrupt latency, and task record ownership ‹ that might be unclear after reading the chapter ÒDeferred Task ManagerÓ in Inside Macintosh:Processes.
This Note is intended for all developers who need to install a lengthy interrupt task capable of running with all interrupts enabled.
About Deferred Task Latency
There may be significant latency incurred between installing a deferred task with DTInstall and when that task is performed. This time is not deterministic and cannot be controlled. Real-time response cannot be guaranteed on Macintosh computers with or without the use of deferred tasks.
About the Ownership of the DeferredTask Reco #rd
When you install a deferred task with DTInstall, you are giving your DeferredTask record to the system; the system owns the record until the routine designated by the DeferredTask recordÕs dtAddr field is entered. During the time the system owns a DeferredTask record, you must not change any of the fields of that record.
Similarly, you must not depend on the contents of the record when it is owned by the system. The system is free to alter the record in any fashion while it has ownership and restores the record to its original state pri Ôor to invoking the deferred task. You must not install a DeferredTask record which is already owned by the system. Finally, you must not use the dtReserved field for any purpose; it should be set to zero prior to installing a deferred task with DTInstall.
Further Reference
¥ Inside Macintosh: Processes, Chapter 6, The Deferred Task Manager
¥ develop, Issue 13, Asynchronous Routines on the Macintosh
Change History
This Technote was originally written by Jim Luther, in July, 1992. Most of the original information has been incorporated into Inside Macintosh: Processes,
The references section has been updated. Information found in the chapter ÒDeferred Task ManagerÓ in Inside Macintosh:Processes, has been deleted.
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