Whether to use TPL or async /await

Question

There is an existing third party Rest API available which would accept one set of input and return the output for the same. (Think of it as Bing's Geo coding service, which would accept address and return location detail)

My need would be is to call this API multiple times (say 500-1000) for a single asp.net request and each call may take close to 500ms to return.

I could think of three approaches on how to do this action. Need your input on which could be best possible approach keeping speed as criteria.

1. Using Http Request in a for loop

Write a simple for loop and for each input call the REST API and add the output to the result. This by far could be the slowest. But there is no overhead of threads or context switching.

2. Using async and await

Use async and await mechanisms to call REST Api. It could be efficient as thread continues to do other activites while waiting for REST call to return. The problem I am facing is that, as per recommendations I should be using await all the way to the top most caller, which is not possible in my case. Not following it may lead to dead locks in asp.net as mentioned here http://msdn.microsoft.com/en-us/magazine/jj991977.aspx

3. Using Task Parallel Library

Using a Parallel.ForEach and use the Synchronuos API to invoke the Server parallely and use ConcurrentDictionary to hold the result. But may result in thread overhead

Also, let me know is there any other better way to handle things. I understand people might suggest to track performance for each approach, but would like to understand how people has solved this problem before

Answer 1

The best solution is to use async and await, but in that case you will have to take it async all the way up the call stack to the controller action.

The for loop keeps it all sequential and synchronous, so it would definitely be the slowest solution. Parallel will block multiple threads per request, which will negatively impact your scalability.

Since the operation is I/O-based (calling a REST API), async is the most natural fit and should provide the best overall system performance of these options.