Parallel Programming in.NET 4.0 Tasks and Threading Ingo Rammer, thinktecture

Ingo Rammer and thinktecture Support and consulting for software architects and developers Architectural Consulting and Prototyping Developer-Coaching and -Mentoring Application Optimization, Troubleshooting, Debugging Architecture and Code Reviews Slides/Samples:

The Problem

128 cores (Yes, this is a real screenshot) 128 cores (Yes, this is a real screenshot)

The future brings more lower speed

Multithreading vs. Parallelism

What do we need? Parallelism, not just multithreading Partitioning of work Queue management Synchronization Today Threads ThreadPool (==> limited API)

.NET <= 3.5 Manual management of parallelism Important Threads: unit of scheduling, not unit of work! ThreadPool: limited API

.NET 4.0 Fine-Grained Parallelism: Task-API and coordination structures (the foundation of it all) Structured Parallelism: Parallel Declarative Parallelism: PLINQ And some underlying optimizations in the ThreadPool

Task API Task t1 = Task.Factory.StartNew(DoSomething); Task t2 = Task.Factory.StartNew(delegate {DoSomething();}); Task t3 = Task.Factory.StartNew(()=>DoSomething()); Something tmp = GetData(); // just dummy parameter Task t4 = Task.Factory.StartNew(p=>((Something)p).DoIt(), tmp); Task t5 = Task.Factory.StartNew(()=>tmp.DoIt()); t1.Wait(); Task.WaitAll(t2,t3,t4); Task.WaitAny(t3,t4,t6); Task t1 = Task.Factory.StartNew(DoSomething); Task t2 = Task.Factory.StartNew(delegate {DoSomething();}); Task t3 = Task.Factory.StartNew(()=>DoSomething()); Something tmp = GetData(); // just dummy parameter Task t4 = Task.Factory.StartNew(p=>((Something)p).DoIt(), tmp); Task t5 = Task.Factory.StartNew(()=>tmp.DoIt()); t1.Wait(); Task.WaitAll(t2,t3,t4); Task.WaitAny(t3,t4,t6);

Tasks with Results Task t1 = Task.Factory.StartNew (() => data.Process()); int val = t1.Result; // blocks until t1 is finished Task t1 = Task.Factory.StartNew (() => data.Process()); int val = t1.Result; // blocks until t1 is finished

Task Continuation var firstTask = new Task (() => First()); var secondTask = firstTask.ContinueWith((t) => Second()); firstTask.Start(); secondTask.Wait(); var firstTask = new Task (() => First()); var secondTask = firstTask.ContinueWith((t) => Second()); firstTask.Start(); secondTask.Wait();

Debugging: Parallel Tasks

Debugging: Parallel Stacks

Structured Parallelism Parallel.Invoke Parallel.Invoke( () => Foo(), () => Bar(), () => Baz()); Parallel.Invoke( () => Foo(), () => Bar(), () => Baz());

Structured Parallelism Parallel.ForEach string[] foo = {"bar","baz","qux"}; Parallel.ForEach(foo, (p) => { DoIt(p); }); // OR...to support stopping: Parallel.ForEach(foo, (p,s) => { DoIt(p); if (p == "baz") s.Stop(); }); // s is implicitly of type ParallelLoopState string[] foo = {"bar","baz","qux"}; Parallel.ForEach(foo, (p) => { DoIt(p); }); // OR...to support stopping: Parallel.ForEach(foo, (p,s) => { DoIt(p); if (p == "baz") s.Stop(); }); // s is implicitly of type ParallelLoopState

int sum2 = lst.Where(p=>p.Index>3123 && p.Index<5892).Sum(p => p.Process()); int sum2 = lst.Where(p=>p.Index>3123 && p.Index<5892).Sum(p => p.Process()); List lst =...; var lst = from p in lst.AsParallel() where p.Index > 3123 && p.Index < 5892 select p; List lst =...; var lst = from p in lst.AsParallel() where p.Index > 3123 && p.Index < 5892 select p; Declarative Parallelism: PLINQ

PLINQ Options lst.AsParallel().WithDegreeOfParallelism(10).AsOrdered().WithMergeOptions(ParallelMergeOptions.FullyBuffered) lst.AsParallel().WithDegreeOfParallelism(10).AsOrdered().WithMergeOptions(ParallelMergeOptions.FullyBuffered)

Cancellation Support Unified cancellation with CancellationSource and CancellationToken Tasks can be manually cancelled, or automatically when parent is cancelled PLINQ-Queries can specify a CancellationToken CancellationSource src = new CancellationSource(); lst.AsParallel().WithCancellation(src.Token).Sum(...); src.Cancel(); CancellationSource src = new CancellationSource(); lst.AsParallel().WithCancellation(src.Token).Sum(...); src.Cancel();

BlockingCollection void ThreadProc() { while (!_workitems.IsCompleted) { var itm = _workitems.Take(); Process(itm); } void ThreadProc() { while (!_workitems.IsCompleted) { var itm = _workitems.Take(); Process(itm); } static BlockingCollection _workItems; void EnqueueProc() { _workItems.Add(123); _workItems.CompleteAdding(); } static BlockingCollection _workItems; void EnqueueProc() { _workItems.Add(123); _workItems.CompleteAdding(); }

ThreadPool Optimizations Local queues Work stealing Locality by LIFO

What you get with.NET 4.0 Fine-Grained Parallelism: Task, Task Structured Parallelism: Parallel.Invoke, Parallel.ForEach Declarative Parallelism: PLINQ //.AsParallel()

Next steps… Think of possible ways to add parallel capabilities to your existing applications. Otherwise you'll only ever use 1/128th of That Big Machine. Resources Daniel Moth's weblog: PFX Team blog: Home:

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