Task

An abstraction over the state and outcome of an async operation. This operation may be executed now, later or never (cancelled before it starts). State:

• not started
• running
• completed

Outcome:

• faulted
• successful - potentially return a result (Task<TResult>)

async

IO Bound: an IO operation utilising the IO Completion ports CPU bound: an operation that requires an active thread.

Concurrent vs Parallel

Concurrent: A scheduler switching between operations Parallel: To operations in progress at the same time. Usually the outcome is to do work faster.

Continuation

A function that is executed after the previous async operation has completed

Starting Task(s)

For CPU bound work

Task.Run(() => CpuBoundWork);

For I/O bound work

Task.Factory.StartNew

Awaiting Task(s)

• This is sequential:

async Task SomeMethod()
{
    await Operation();
    DoSomethingElse(); // a continuation that executes after Operation
}

• To wait for multiple Tasks in progress:

// This would take as long as the longest task
await Task.WhenAll(task1, task2, task3);

// This would take as long as the quickest task
await Task.WhenAny(task1, task2, task3);

Marking a method async vs returning a Task

• If there is only one async operation, favour returning a Task to avoid generating an unnecessary state machine
• When there are multiple async operations, it is usually preferable to mark the method as async.

References

• Danial Marbach's Webinar