Android Concurrency & Synchronization: Part 6
Android’s UI has several design Message constraints • Android therefore supports various concurrency idioms for processing long-running operations in background thread(s) & communicating with the UI Thread • Handlers, Messages, & Runnables • Allows an app to spawn threads that perform background operations & publish results on the UI thread
Android Concurrency: The Active Object Pattern
Challenge: Invoking Methods in Another Thread Context • Android clients that access objects running in separate threads of control • A “client” is any Android code that invokes a object’s method, e g , • A background Thread invoking sendMessage() on a Handler associated with the UI Thread • More generally, any Threads that interact
Threading overview - UMD
Do work on a background thread, but update the UI on the UI Thread Android provides several methods that are guaranteed to run in the UI Thread booleanView post(Runnable action) void Activity runOnUiThread(Runnable action)
Retrofitting Concurrency for Android Applications through
java lang Thread to fork concurrent asynchronous execu-tion, it is cumbersome to communicate with the main thread Android framework provides a better alternative, AsyncTask , which is a high-level concurrent construct AsyncTask can also interact with the UI thread by updating the UI via event handlers For example, the event handler onPostExecute
Finding Errors in Multithreaded GUI Applications
• UI thread: a single special thread to handle UI events • Non-UI thread: other threads • UI-accessing method: a method whose execution may read or write a GUI object • Safe UI method: message-passing methods to execute code on the UI thread 12 A GUI Application UI-thread Non-UI thread asyncExec( ) Safe UI method void runTask() {
Efficiently Manifesting Asynchronous Programming Errors in
Specifically, UI thread fetches system or user events off an event queue, and dispatches them either to a responsible app component’s handler or to a UI widget’s event handler These handlers run on the UI thread and exclusively update GUIs if necessary Due to this single-GUI-thread model, it is vital to avoid block-ing the UI thread
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Android’s UI Thread The Handler class Conceptual view Parallel computation running in a process Implementation view A program counter and a stack
Android Tips and Tricks Brian Ricks Fall 2015
Threads - Handler The Handler class provides a callback framework to handle operations in a different thread from the one invoking the callback – Basic steps: Instantiate some subclass of Handler in the UI thread Pass this instance to the worker thread which will update the UI When you want to update UI in this worker thread, call
Refactorings for Android Asynchronous Programming
to communicate with the main thread Android framework provides a better alternative, AsyncTask, which is a high-level concurrent construct AsyncTask can also interact with the UI thread by updating the UI via event handlers For example, the event handler onPostExecute executes after the task is finished, and can update the UI with the task
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