MVC 4 Web Api：从操作返回任务

Question

Probably there is some mess in my head, but I see a kind of confusion in the following:

• Web API controllers are derived from the ApiController class, where the main method is ExecuteAsync, which make the request go through the pipe of filters and action, returning Task at the end;
• Web API actions support ability to return object of type Task, utilizing TPL or async/await.

My question is: do I really benefit from constructing and runing tasks within API actions? As far as I understand, the goal to return threads back into ASP.NET threadpool ASAP is already carried out by ApiController.ExecuteAsync infrastructure, therefore additional level of async gives me nothing (except if I need cancellation for task or performing operations in backend in parallel).

Any thoughts? Thanks.

Answer 1

As with any parallel programming the answer is unfortunately: it completely depends on the kind of processing you're doing.

For starters, the ASP.NET runtime is already providing concurrency per request. Therefore if the work you're doing is entirely compute bound then there is very little benefit to using async. The exception to that rule is if the data your processing in the request is very large and, thus, would benefit from further concurrency.

The most important scenarios where it does make sense to use async is when you're doing any kind of I/O work (disk I/O or network I/O). For example when your ASP.NET controller code...

• communicates with another backend web service
• communicates with the database server
• reads/writes file information to the disk

You want to use async in these cases because there is wait time while the I/O requests are fulfilled: either disk or network latency. By using async you free the CPU thread that would have otherwise been blocked waiting on that data so that it can process some other compute bound work.