PDF Presentation - Uplinq

Event Handling
• A backlog in the event queue translates into perceived delay for the user
– Validate that the event arrival rate of your design, combined with the other system events can be
processed by the system without a queue becoming so deep that it impacts the users perception
of responsiveness, or that the system elects to drop events
– When exceeding this threshold one needs to consider if the "event" being processed is more
optimally treated as data. Touch screen events are a common example. Handwriting recognition
improves with the number of samples per second. Treating every sample as an event can flood
the even handling mechanism. Grouping down events into a list of data, with a time derived event,
can improve performance.
• Event prioritization and/or creating independent UI tasks can have an advantage
– Take the example of a single threaded UI downloading a web page. If single threaded, and polling
a queue, the page download would not be interruptible until the download is complete. This is an
extreme hypothetical, example.
• Do not use the event queue as a polling mechanism
– For example, in Brew ® , do not post an event to yourself, check some conditions in the event
handler, and then re-post the same event if the condition hasn't been satisfied yet. If you must
periodically check some condition, use a timer with a non-zero delay and check the conditions
in the timer callback handler.
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