Huseyin YILDIZ Software Design Engineer Microsoft Corporation SESSION CODE: DEV314

Op1 Op2 Op3 Op4 Op5 CPU1 CPU2 CPU3 CPU4

IEnumerable records = GetRecords(); List results = new List (); foreach(Record record in records) { Result res = ProcessRecord(record); // non-trivial computation per record if (Filter(res)) results.Add(res); // check if result matches our criteria, if so add it into results } // can also be expressed as a simple LINQ statement List results = records.Select(rec => ProcessRecord(rec)).Where(res => Filter(res)).ToList();

IEnumerable records = GetRecords(); List results = new List (); int numWorkers = Environment.ProcessorCount; int activeWorkers = numWorkers; IEnumerator enumerator = records.GetEnumerator(); ManualResetEvent completionEvent = new ManualResetEvent(false); for(int i = 0; i < numWorkers; i++) { ThreadPool.QueueUserWorkItem(delegate { // launch P workers while(true) { Record currentRecord; lock (enumerator) { // grab a record under the lock before processing it if (!enumerator.MoveNext()) break; currentRecord = enumerator.Current; } Result res = ProcessRecord(currentRecord); // non-trivial computation per record if (Filter(res)) // check if result matches our criteria { lock(results) results.Add(res); // if so add it into results list under a lock } if (Interlocked.Decrement(ref activeWorkers) == 0) completionEvent.Set(); }); } completionEvent.WaitOne(); // wait until all workers are done

SAME CODE PARALLELIZED USING PLINQ

Visual Studio IDE.NET Framework 4 Parallel Debugger Concurrency Visualizer Thread Pool Task Scheduler Task Parallel Library Parallel LINQ Sync Primitives Concurrent Collections CLR

PARALLEL LOOPS src Thread 1 rec 1 rec 1 Thread P rec P+1 rec P+1 rec 2P+1 rec 2P+1 rec 2P rec 2P rec 3P rec 3P rec P Parallel.For(0, 100, i => DoWork(i)); Parallel.ForEach(src, rec => DoWork(rec)); Thread 1 i=0 Thread P Thread 2 i=C+1 i=C+2 i=C+3 i=1 i=2 i=P*C+1 i=P*C+2

// Breaking from a parallel loop Parallel.For(0, 1000, (i, state) => { if (SearchFunc(i)) state.Stop(); } // Controlling Degree Of Parallelism ParallelOptions po = new ParallelOptions() { MaxDegreeOfParallelism = 4 }; Parallel.ForEach(source, po, element => ProcessRecord(element) } // Using thread local state Dictionary counts = GetGlobalCounts(); Parallel.ForEach(enumSource, () => { //once per worker thread local init return new List (); }, (record, loopState, threadLocal) => { // actual loop body var result = ProcessRecord(record); if (result.InterestingFlag) threadLocal.Add(result); //cache results }, (threadLocal) => { //end of loop, once per worker combine delegate lock (counts) foreach (Result res in threadLocal) counts[res.GUID] += res.Count; });

PARALLEL LINQ

HOW PLINQ WORKS src Thread 1 where f(x) select y(x) Sum() Thread P where f(x) select y(x) Sum()

PARALLEL LINQ (cont’d)

Enqueue Global Queue (FIFO) Thread 1 Dispatch Loop Thread 2 Dispatch Loop Thread N Dispatch Loop Dequeue T2T2 T3T3 T1T1

Enqueue Global Queue (FIFO) Thread 1 Dispatch Loop Thread 1 Local Queue (LIFO) Thread 2 Dispatch Loop Thread 2 Local Queue (LIFO) Thread N Dispatch Loop Thread N Local Queue (LIFO) Dequeue Enqueue Steal T2T2 T3T3 T4 T4 T5T5 T6T6 T7T7 T8T8 T1T1

// Producer consumer pattern BlockingCollection bc = new BlockingCollection (); // Start the producer Task Task t1 = Task.Factory.StartNew(() => { while(!streamReader.EndOfStream) bc.Add(streamReader.ReadLine()); bc.CompleteAdding(); }); // Start the consumer Task Task t2 = Task.Factory.StartNew(() => { try { // Consume from the blocking collection while (true) Console.WriteLine(bc.Take()); } catch (InvalidOperationException) { // IOE thrown from Take() indicated completed collection Console.WriteLine("That's All!"); } });

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Required Slide Track PMs will supply the content for this slide, which will be inserted during the final scrub.

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