async await best practices


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


  • faulted
  • successful - potentially return a result (Task)


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.


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


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.