 Parallel Programming in C# Pro.Net Programming in C#, Adam Freeman

Parallel C#  Task Parallel Library (TPL)  TPL tasks vs. Threads  Benefits & Pitfalls of Parallel Programming  Overhead  Coordinating fata  Scaling Applications

Task Programming  Creating and starting tasks  Task.Factory.StartNew()  Task.Start()  Setting task state  System.Action  Passing parameters to tasks  Getting a result  Task.Result

Task Programming  Task creation options  PreferFairness  LongRunning  AttachedToParent  Identifying tasks  Task.CurrentId

Cancelling tasks  Simpler, more consistent and reduced risk task creation  Steps:  Create a new instance of CancellationTokenSource  Call CancellationTokenSource.Token property to get a Cancellationtoken  Create a new task with this token  Call Start() method of the task to start this task  Call CancellationTokenSource.Cancel() method to cancel the task

Cancelling tasks  Who is responsible of cancelling a task?  Cancellation procedure in a task  Polling  Using a delegate  Cancelling with a wait handle  Cancelling several tasks  Composite cancellation tokens  Determine task is cancelled

Waiting time to pass  Sleeping  Using cancellation token wait handle  Using classic Thread.Sleep()  Using Thread.SpinWait()

Waiting for tasks  What if there is no Task.Result?  Waiting for single task: Wait(), Wait(CancellationToken), Wait(Int32), Wait(TimeSpan), Wait(Int32, CancellationToken)  Wait for several tasks: WaitAll(), WaitAny()

Handling exceptions  Basic exceptions: AggregateException  Iterative handler: AggregateException.Handle()  Reading task properties:  IsCompleted  IsFaulted  IsCancelled  Exception

Getting status of a task  Created  WaitingForActivation || WaitingToRun  Running  WaitingForChildrenToComplete  RanToCompletion  Canceled  Faulted

Executing tasks lazily  Execute task when needed.  Anonymous functions  Lazy

Common problems  Task dependency deadlock  Local variable evaluation  Excessive spinning