Types of Frameworks in AsyncTask (Part 1)schmidt/cs891s/2018-PDFs/L2... · 2018. 3. 14. · 3 • Understand what black-box & white-box framework are… & how AsyncTask implements

Douglas C. [email protected]

www.dre.vanderbilt.edu/~schmidt

Institute for Software Integrated Systems

Vanderbilt University Nashville, Tennessee, USA

Types of Frameworks in AsyncTask (Part 1)

mailto:[email protected]

2

Learning Objectives in this Part of the Lesson• Understand what black-box & white-box framework are…

See www.dre.vanderbilt.edu/~schmidt/PDF/DRC.pdf

White-boxBlack-box

http://www.dre.vanderbilt.edu/%7Eschmidt/PDF/DRC.pdf

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• Understand what black-box & white-box framework are… & how AsyncTaskimplements both types of frameworks

Learning Objectives in this Part of the Lesson

White-boxBlack-box

4

Common Types of Frameworks

5

Common Types of Frameworks• Black-box frameworks only

require understanding external interfaces of objects

6


require understanding external interfaces of objects• Framework elements typically

reused by parameterizing & assembling objects

7




• White-box frameworks require understanding some parts of the framework implementation

8




• White-box frameworks require understanding some parts of the framework implementation• Framework elements typically

reused by subclassing & overridding

9


• Each category of OO framework uses different sets of patterns

• Black-box frameworks only require understanding external interfaces of objects


10



See en.wikipedia.org/wiki/Strategy_pattern& en.wikipedia.org/wiki/Decorator_pattern



Black-box frameworks apply patterns that emphasize extensibility via object composition

http://en.wikipedia.org/wiki/Strategy_patternhttp://en.wikipedia.org/wiki/Decorator_pattern

11


See en.wikipedia.org/wiki/Template_method& en.wikipedia.org/wiki/State_pattern




White-box frameworks apply patterns that emphasize

extensibility via subclassing

http://en.wikipedia.org/wiki/Template_methodhttp://en.wikipedia.org/wiki/State_pattern

12


require understanding external interfaces of objects



Android’s AsyncTask combines elements of black-box & white-box frameworks

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White-box Elements of the AsyncTask Framework

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: DownloadTask

: WorkerRunnable

: DefaultExecutor

: ThreadedDownload

doInBackground()

execute()

execute()onPreExecute() call()

onPostExecute()postResult()

UI Thread

White-box Elements of the AsyncTask Framework • White-box framework

elements enable long duration operations to interact with UI thread

See en.wikipedia.org/wiki/Template_method

BackgroundThread

http://en.wikipedia.org/wiki/Template_method

15

: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread

Template method

• White-box framework elements enable long duration operations to interact with UI thread

BackgroundThread

: DownloadTask

: ThreadedDownload

See xp123.com/wwake/fw/ch12-bb.htm for more on framework design


http://xp123.com/wwake/fw/ch12-bb.htm

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: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread

• Framework dictatescontrol flow via hook method callbacks

BackgroundThread

: DownloadTask

: ThreadedDownload


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: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread

BackgroundThread

Initialization actions


: DownloadTask

: ThreadedDownload


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: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread

Perform long-running task


BackgroundThread

: DownloadTask

: ThreadedDownload


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: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread

Display results in UI


BackgroundThread

: DownloadTask

: ThreadedDownload


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: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread


BackgroundThread

: DownloadTask

: ThreadedDownload


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: WorkerRunnable

: DefaultExecutor

doInBackground()

execute()



UI Thread


BackgroundThread

ThisTemplate Method variant allows hook methods to run in different threads

: DownloadTask

: ThreadedDownload


22

Black-box Elements of the AsyncTask Framework

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• Black-box framework elements control the background thread(s)

Black-box Elements of the AsyncTask Framework: Download

Task: WorkerRunnable

: Executor: ThreadedDownload

doInBackground()

execute()


postResult()

UI Thread

BackgroundThreads

See en.wikipedia.org/wiki/Strategy_pattern

onPostExecute()

http://en.wikipedia.org/wiki/Strategy_pattern

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• Black-box framework elements control the background thread(s)• Default concurrency

model has changed

: DownloadTask

: WorkerRunnable


doInBackground()

execute()

execute() call()

postResult()

UI Thread

BackgroundThreads

See developer.android.com/reference/android/os/AsyncTask.html

onPreExecute()

onPostExecute()


http://developer.android.com/reference/android/os/AsyncTask.html

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• Black-box framework elements control the background thread(s)• Default concurrency

model has changed

: DownloadTask

: WorkerRunnable


doInBackground()

execute()

execute() call()

postResult()

UI Thread

BackgroundThread

onPreExecute()

onPostExecute()


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• AsyncTask can be configured via a # of Executor strategies

: DownloadTask

: WorkerRunnable


doInBackground()

execute()

execute() call()

postResult()

UI Thread

BackgroundThread

sDefaultExecutor = SERIAL_EXECUTOR

onPreExecute()

onPostExecute()

See developer.android.com/reference/java/util/concurrent/Executor.html


http://developer.android.com/reference/java/util/concurrent/Executor.html

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: DownloadTask

: WorkerRunnable


doInBackground()

execute()

execute() call()

postResult()

UI Thread

BackgroundThread

onPreExecute()

onPostExecute()



SERIAL_EXECUTOR executes tasks one at a time in serial order

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: DownloadTask

: WorkerRunnable




SERIAL_EXECUTOR executes tasks one at a time in serial order

class SerialExecutor implements Executor {final ArrayDeque mTasks = new ArrayDeque();Runnable mActive;

public synchronized void execute(final Runnable r) {mTasks.offer(() -> { try { r.run(); }

finally { scheduleNext(); }}});if (mActive == null) scheduleNext();

}

protected synchronized void scheduleNext() {if ((mActive = mTasks.poll()) != null) THREAD_POOL_EXECUTOR.execute(mActive);

}}

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: DownloadTask

: WorkerRunnable


doInBackground()

execute()



UI Thread

BackgroundThread

Some apps need to run AsyncTask objects in parallel instead of serially



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: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

Allows multiple long duration tasks to run in parallel within a process

onPreExecute()

onPostExecute()

executeOnExecutor(THREAD_POOL_EXECUTOR,params)


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: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

onPreExecute()

onPostExecute()

executeOnExecutor(THREAD_POOL_EXECUTOR,params)


THREAD_POOL_EXECUTOR can be used to execute tasks in parallel

static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();

static final int CORE_POOL_SIZE = CPU_COUNT + 1;static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;static final int KEEP_ALIVE = 1;

static final BlockingQueue sPoolWorkQueue =new LinkedBlockingQueue(128);

static Executor THREAD_POOL_EXECUTOR = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE,

KEEP_ALIVE, TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);

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: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

onPreExecute()

onPostExecute()

executeOnExecutor(MY_CUSTOM_EXECUTOR,params)

See developer.android.com/reference/java/util/concurrent/ExecutorService.html


http://developer.android.com/reference/java/util/concurrent/Executor.html

33


: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

onPreExecute()

onPostExecute()

executeOnExecutor(executorStrategy,params)


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: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

SERIAL_EXECUTOR, THREAD_POOL_EXECUTOR,

or custom Executor strategy

onPreExecute()

onPostExecute()



35


: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

SERIAL_EXECUTOR, THREAD_POOL_EXECUTOR,

or custom Executor strategy

onPreExecute()

onPostExecute()



36


: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

onPreExecute()

onPostExecute()


Executor treated as a black-box


37

• AsyncTask ensures certain operations are safe without explicit synchronizations

: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

onPreExecute()

onPostExecute()



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• AsyncTask ensures certain operations are safe without explicit synchronizations, e.g.• Set fields in the

AsyncTask ctoror onPreExecute(), & refer to them in doInBackground()

: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

onPostExecute()

onPreExecute()



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• AsyncTask ensures certain operations are safe without explicit synchronizations, e.g.• Set fields in the

AsyncTask ctoror onPreExecute(), & refer to them in doInBackground()

• Set member fields in doInBackground()& refer to them inonProgressUpdate()& onPostExecute()

: DownloadTask

: WorkerRunnable


doInBackground()

execute() call()

postResult()

UI Thread

BackgroundThreads

onPreExecute()

onPostExecute()



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End of Types of Frameworks in AsyncTask (Part 2)

Slide Number 1Learning Objectives in this Part of the LessonLearning Objectives in this Part of the LessonSlide Number 4Common Types of FrameworksCommon Types of FrameworksCommon Types of FrameworksCommon Types of FrameworksCommon Types of FrameworksCommon Types of FrameworksCommon Types of FrameworksCommon Types of FrameworksSlide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39End of Types of Frameworks in AsyncTask (Part 2)

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Types of Frameworks in AsyncTask (Part 1)schmidt/cs891s/2018-PDFs/L2... · 2018. 3. 14. · 3 • Understand what black-box & white-box framework are… & how AsyncTask implements