“Parallel Programming with

“Parallel Programming with Async and Await”

Joe Hummel, PhDjoe@joehummel.netTechnical Staff: PluralsightAdjunct Professor: UIC, LUC

http://www.joehummel.net/downloads.html

MotivationExecution modelParallel programming with TasksParallel programming with Async / AwaitDemos

2

Agenda

3

Async vs. Parallel?

Async programming:Better responsiveness…GUIs (desktop, web, mobile)CloudWindows 8

Parallel programming:Better performance…EngineeringOil and GasPharmaScienceSocial media

C

C

C

C

C

C

C

C

Disk and network I/O

tasks

number crunching and big data processing

4

Execution model

C

C

C

C

C

C

C

C

Main

thread

C

Main

<<start Work>>

if…

while…

Work

Stmt1;

Stmt2;

Stmt3;

Main

<<start Work1>>

<<start Work2>>

if…

while…

Work1

Stmt1;

Stmt2;

Stmt3;

Work2

Stmt4;

Stmt5;

Stmt6;

Worker

thread

Worker

thread

Worker

thread

Main

thread

Threads

share,

run asynchronously

Threads run in parallel

Single core:

Multicore:

Threads (.NET 1.0)Async DelegatesQueueUserWorkItemBackgroundWorkerTask Parallel Library (.NET 4.0)Async / Await (.NET 4.5)

5

Numerous ways to program

Easier…

Mandelbrot set…

6

Demo ― Performance

Programming model based on concept of a Task

7

Task-based

Task

==

a unit of work

; an object denoting an

ongoing operation or computation

.

8

Task-based execution model

C

C

C

C

C

C

C

C

Windows Process (.NET)

App

Domain

App

Domain

App

Domain

.NET Thread

Pool

worker

thread

worker

thread

worker

thread

worker

thread

Parallel.For

( ... );

task

task

task

task

Task Parallel Library

Resource Manager

Task Scheduler

Windows

Asian options financial modeling…

9

Demo ― Responsiveness

10

Async solution #1: Tasks

void button1_Click(…){ var uictx = // grab UI thread context to run UI task: TaskScheduler.FromCurrentSynchronizationContext(); Task.Factory.StartNew(()=> { return DoLongLatencyOp(); } ).ContinueWith((antecedent) => { lstBox.Items.Add(antecedent.Result); }, uictx // execute this task on UI thread: );}

void button1_Click(…){ var result = DoLongLatencyOp(); lstBox.Items.Add(result);}

11

Async solution #2: Async / Await

void button1_Click(…){ var result = DoLongLatencyOp(); lstBox.Items.Add(result);}

async void button1_Click(…) { var result = await Task.Run( () => DoLongRunningOp()); lstBox.Items.Add(result); }

T

ells compiler that method *may* perform an async, long-latency op

Tells compiler to execute operation but

don’t wait.

Instead, start op as a separate task, and setup a continuation to execute the remaining code when op finishes ― RUNNING ON THE SAME THREAD CONTEXT!

For operations that may involve long latencyFile and network I/O are the classic use-caseFor chunks of work you want to run in parallelAnd you have multi-core hardware

12

When to use

Async

/ Await?

Hides the complexities of async programmingNo visible callback, predictable exception handling, …Think chunky, not chattyi.e. designed for coarse-grain work / long-latency operationsDesigned to be used with APM patternAsynchronous Programming ModelAPIs that offer async calls via APM?File I/ONetwork I/OWindows 8 API

13

Observations…

Async web calls are a classic use-case

14

Example

private byte[] GetURLContents(string url) { var content = new MemoryStream(); var webReq = (HttpWebRequest)WebRequest.Create(url); using (WebResponse response = webReq.GetResponse()) { using (Stream responseStream = response.GetResponseStream()) { responseStream.CopyTo(content); } } return content.ToArray();}

Synchronous Version

Asynchronous web requests…Work bottom-up changing sync calls to async callsAdd await, async, and Task or Task<T> as needed

15

Demo

private async Task<byte[]> GetURLContentsAsync(string url) { var content = new MemoryStream(); var webReq = (HttpWebRequest)WebRequest.Create(url); using (WebResponse response = await webReq.GetResponseAsync()) { using (Stream responseStream = response.GetResponseStream()) { await responseStream.CopyToAsync(content); } } return content.ToArray();}

Asynchronous

Version

16

That’s it!

Thread-based execution model at very bottomTask-based execution model on topFor Performance:Prefer Task Parallel LibraryFor Responsiveness:Prefer Async / Await

17

Summary

Presenter: Joe HummelEmail: joe@joehummel.netMaterials: http://www.joehummel.net/downloads.html For more info:MSDN Magazine, October 2011 (3 articles):“Easier Asynchronous Programming with the New Visual Studio Async CTP”“Pause and Play with Await”“Async Performance: Understanding the Costs of Async and Await”

18

Thank you for attending!