Stephen Toub ([email protected]) Parallel Computing Platform Microsoft Corporation.

An Insider’s View to Concurrency at MicrosoftStephen Toub ([email protected])Parallel Computing PlatformMicrosoft Corporation

Agenda

• Why We (I) Care• What We’ve Built for Developers• What We’re Building for Developers

Moore’s Law: Alive and Well

http://upload.wikimedia.org/wikipedia/commons/2/25/Transistor_Count_and_Moore%27s_Law_-_2008_1024.png

MS Apps Using ParallelismExample: Visual Studio

• Background compilation

• Regex-based file search

• Graph layout• Reference

highlighting• IntelliSense sorting• Project build system

• Code analysis• Unit testing• …

But it’s not just about core count…• Increasingly connected applications

• More latency• e.g. everything as a service

• More UI responsiveness problems• e.g. the toilet bowl of death

• More scalability issues• Server, Cloud

• e.g. streaming data sources, data distribution

• Client• e.g. modeling interacting biological entities

• Async-only APIs• e.g. Silverlight

The Challenges of Concurrency• A different way of thinking

• Forcing the square peg (concurrency) into the round hole (sequential) is a common (inadequate) mistake

• Parallel patterns are not prevalent, well known, nor easy to implement• CS curriculum is still largely “sequential”: Cormen, et. al; Knuth; etc.

• A different way of writing software• Indeterminate program behavior

• No longer: “A happens, then B happens, then C happens”• It’s just: “A, B, and C happen”

• With distinct costs, too• Deadlocks, livelocks, latent race conditions, priority inversions,

hardware-specific memory model reordering, …

• Businesses have little desire to go deep• Best devs should focus on business value, not concurrency• Need simple ways to allow all devs to write concurrent code

Example: Searching and Sorting

IEnumerable<RaceCarDriver> drivers = ...;var results = new List<RaceCarDriver>();foreach(var driver in drivers){ if (driver.Name == queryName && driver.Wins.Count >= queryWinCount) { results.Add(driver); }}results.Sort((b1, b2) => b1.Age.CompareTo(b2.Age));

Manual Parallel Solution

IEnumerable<RaceCarDriver> drivers = …;var results = new List<RaceCarDriver>();int partitionsCount = Environment.ProcessorCount;int remainingCount = partitionsCount;var enumerator = drivers.GetEnumerator();try { using (var done = new ManualResetEvent(false)) { for(int i = 0; i < partitionsCount; i++) { ThreadPool.QueueUserWorkItem(delegate { while(true) { RaceCarDriver driver; lock (enumerator) { if (!enumerator.MoveNext()) break; driver = enumerator.Current; } if (driver.Name == queryName && driver.Wins.Count >= queryWinCount) { lock(results) results.Add(driver); } } if (Interlocked.Decrement(ref remainingCount) == 0) done.Set(); }); } done.WaitOne(); results.Sort((b1, b2) => b1.Age.CompareTo(b2.Age)); }}finally { if (enumerator is IDisposable) ((IDisposable)enumerator).Dispose(); }

LINQ Solution

IEnumerable<RaceCarDriver> drivers = ...; var results = from driver in drivers where driver.Name == queryName && driver.Wins.Count >= queryWinCount orderby driver.Age ascending select driver;

.AsParallel()

P

DemoPLINQ

Visual Studio 2010Tools, Programming Models, Runtimes

Parallel Pattern Library

Resource Manager

Task Scheduler

Task Parallel Library

Parallel LINQ

Managed NativeKey:

ThreadsOperating System

Concurrency Runtime

Programming Models

ThreadPool

Task Scheduler

Resource Manager

Data

Stru

ctu

res

Data

Str

uctu

res

Tools

Tooling

ParallelDebugge

r Tool Windows

ProfilerConcurren

cy Visualizer

AsyncAgentsLibrary

UMS Threads

.NET Framework 4 Visual C++ 2010Visual Studio2010

Windows

Investigations for the future…

This is somesynchronous code with .NET 4…

public void CopyStreamToStream(Stream source, Stream destination){    byte[] buffer = new byte[0x1000];    int numRead;    while ((numRead = source.Read(buffer, 0, buffer.Length)) != 0)    {        destination.Write(buffer, 0, numRead);    }}

This is an expert’s asynchronous code with .NET 4…

public void CopyStreamToStream(Stream source, Stream destination){    byte[] buffer = new byte[0x1000];    int numRead;    while ((numRead = source.Read(buffer, 0, buffer.Length)) != 0)    {        destination.Write(buffer, 0, numRead);    }}

public IAsyncResult BeginCopyStreamToStream( Stream source, Stream destination){    var tcs = new TaskCompletionSource<object>();    byte[] buffer = new byte[0x1000];

    Action<IAsyncResult> readWriteLoop = null;    readWriteLoop = iar =>    {        try        {            for (bool isRead = iar == null; ; isRead = !isRead)            {                switch (isRead)                {                    case true:                        iar = source.BeginRead(buffer, 0, buffer.Length,  readResult =>                        {                            if (readResult.CompletedSynchronously) return;                            readWriteLoop(readResult);                        }, null);                        if (!iar.CompletedSynchronously) return;                        break;

                    case false:                        int numRead = source.EndRead(iar);                        if (numRead == 0)                        {                            tcs.TrySetResult(null);                            return;                        }                        iar = destination.BeginWrite(buffer, 0, numRead, writeResult =>                        {                            if (writeResult.CompletedSynchronously)  return;                            destination.EndWrite(writeResult);                            readWriteLoop(null);                        }, null);                        if (!iar.CompletedSynchronously) return;                        destination.EndWrite(iar);                        break;                }            }        }        catch (Exception e) { tcs.TrySetException(e); }    };    readWriteLoop(null);

    return tcs.Task;}

public void EndCopyStreamToStream(IAsyncResult asyncResult){    ((Task)asyncResult).Wait();}

A compiler could do the work for us…

public void CopyStreamToStream(Stream source, Stream destination){    byte[] buffer = new byte[0x1000];    int numRead;    while ((numRead = source.Read(buffer, 0, buffer.Length)) != 0)    {        destination.Write(buffer, 0, numRead);    }}

public Task CopyStreamToStream(Stream source, Stream destination){    byte[] buffer = new byte[0x1000];    int numRead;    while ((numRead = await source.ReadAsync(buffer, 0, buffer.Length)) != 0)    {         await destination.WriteAsync(buffer, 0, numRead);    }}

public Task CopyStreamToStream(Stream source, Stream destination){    byte[] buffer = new byte[0x1000];    int numRead;    while ((numRead = await source.ReadAsync(buffer, 0, buffer.Length)) != 0)    {         await destination.WriteAsync(buffer, 0, numRead);    }}

Q&A

© 2010 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.