Ts threading

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Threading

Muhammad Mateen| Android Mentor

Threading Topics covered in the presentation

• UI Thread

• Loppers & Handlers

• Async Tasks

• Intent Services

• Executor

• Executor Service

• Callables & Futures


Threading

UI Thread


• When an application is launched, the System creates a Thread

of execution called the Main Thread or the UI Thread.

• Called the UI Thread because it is this thread which interacts

with the UI widgets.

• Don’t execute tasks that take more then 5 seconds? Why ?

Threading

UI Thread


•Things to remember

• No long operations

• Don’t interact other threads with UI thread

•The UI thread runs as a NORMAL PRIORITY thread.

Threading

UI Thread


•UI Thread acts as a Pipeline Thread, similar to those from Swing or

any other UI Framework

•Each action is feed into a Pipeline, and processed

•Any long operation can starve other tasks in the queue

•We can use HANDLERS to interact with this queue

Threading

Loopers and Handlers


•Ordinary thread to Pipeline thread

•Loopers implements the loop

•Handler feeds the task into Queue associated with the Thread

•Together, multi-threaded processes can be handled

•Handlers detect the Looper, implicitly

•Each Handler is always tied to one Looper

Threading

Async Tasks


•Easiest way to offload onto a separate thread.

• Executes task off the UI thread and post result on UI

• Not used for long processes (why ? )

• Works parallel (for less 4.x)

• Tied with Activity

• On memory shortage, it likely to be killed

Threading

Async Tasks


• Why should be take care of point 3 ?

• Well for one the API documentation says so

• Secondly the Resource Queue is created by the System

• Avoid straining resources that you did not allocate

Threading

Async Tasks


Methods

• onPreExecute()

• doInBackground()

• onProgressUpdate()

• onPostExecute()

Threading

Intent Service


• Subclass of Service Class

• Work Queue Process

• Runs off the UI Thread

• Can place long process in onHandleIntent()

• Manages Worker Thread itself.

• Can get a out-of-the-box-queue

• Broadcast intents

Threading

Executor


• Pool of runnable tasks

• Decouples the mechanics of a Task Submission from the process

of how they will be executed.

•We use this instead of creating Threads separately.

Threading

Executor Service


• Add lifecycle methods to Executor

• Create N number of thread pool

• Or Executors.newSingleThreadExecutor() for a Single runnable

pool

• shut down a executor will reject new Tasks

Threading

Executor Service


•Methods

shutDown() – don’t kill the running tasks

shutDownNow() – kill the running tasks

• Unused ExecutorService can be shutdown, to claim for its

resources

•Upon termination, an executor has no tasks actively executing,

no tasks awaiting execution, and no new tasks can be submitted

Threading

Callables And Futures


•Biggest Issue with Runnable ?

•Callable return values after completion

• Submitting callable to executor returns a Future

• Futures can be used to check Callable’s status

•Use the get method to retrieve the result of a Future

Ts threading

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