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Procrastinator: Pacing Mobile Apps’ Usage of the Network. mobisys 2014. Outline. Motivation Design and Implementation Evaluation Overhead. Motivation.
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Procrastinator: Pacing Mobile Apps’ Usage of the Network mobisys 2014
Outline • Motivation • Design and Implementation • Evaluation • Overhead
Motivation • App developers rely heavily on prefetching network content at the launch of an app to hide the network latency of cellular communication.
Motivation • For some users, they don’t visit off-screen content. • This waste harm three sets of users • 1. users that are always conscious about data because they are on a pay-per-byte plan. • 2.users that start their monthly cellular billing cycle with a large number of bytes, but eventually run low and want the remaining bytes to last them through the end of their cycle. • 3.users that have large data plans at home but are temporarily roaming.
How to save data? • 1. It should automatically identify asynchronous network calls that are candidates for procrastination • 2. decide whether to procrastinate each candidate call, and when to execute a previously procrastinated call. • present Procrastinator • Instrumenter • Procrastinator Runtime
How to prefetch network content? • Three programming patterns • Pattern 1: the app developer assigns an image to an image element that is not visible on screen. example: news reader app only top 3 or 4 is visible. • Pattern 2: additional processing is required before displaying the fetched data. The UI elements may not be visible. • Pattern 3: the assignment to the UI element is delayed even further. For example, weather app. At launch, the app fetches data about hurricane warnings, which it stores in a global variable. The data is used only if the user navigates to a specific tab or a “page”.
How to look for prefetching patterns? • Pattern 1 • the instrumenter looks for any HTTP fetch API calls that are set to a UI element’s source.
How to look for prefetchingpatterns? • Pattern 2 • the developer passes a callback function to the network call. The network call asynchronously fetches data and invoke the callback with the data. The UI elements are then accessed and updated in the callback. • static analysis: • find the callback method associated with the call • generate a conservative call graph that is rooted in the callback method. • analyze code in the conservative call graph to discover all UI elements being update • analyze code in the call graph to ensure it has no side effect.
How to look for prefetchingpatterns? • Pattern 3 • two passes of static analysis • In the first pass • analyze network callbacks to identify global variables used in store operations.(similar to Pattern 2) • In the second pass • analyze the rest of the app code to identify code where the same global variables are accessed in load operations.
Procrastinator Runtime • Procrastinator Runtime behavior for pattern 1,2
Procrastinator Runtime • Procrastinator Runtime behavior for pattern 3
Define • necessary • If we cannot deduce whether the content of web objects is used in the screen, we conservatively assume them to be “necessary” • If a web object is not necessary, then it is either “skipped” or “prefetched” • skipped • If Procrastinator correctly deduces that a network is not necessary and doesn’t download it. • prefetched • If Procrastinator allows an object to be downloaded that is not necessary. (delayed)
