Asynchronous multiple Web Service requests with ordered result

Question

Given a certain number of request objects (max 9), i need to call a web service endpoint the same number of times asynchronously. With .NET 4.0, we used delegate and IAsyncResult to achieve this.

Is there a better way to do this with asyc/await, TPL or both of them combined with .NET 4.6.1?

Will using Parallel.ForEach with ConcurrentBag be optimal as suggested in this answer?

Synchronous Code Example:

public List<WbsResponse> GetWbsResults()
{
    List<WbsRequest> requests = CompileWbsRequests();
    List<WbsResponse> results = new List<WbsResponse>();
    foreach (var request in requests)
    {
        //Call same web service endpoint n number of times
        var response = CallWebService(request);
        results.Add(response);
    }

    //do something with results

    return results;
}

private WbsResponse CallWebService(WbsRequest request)
{
    //Call web service
}

Edit/Update 1: Based on @Thierry's answer, i've created a sample code assuming there's an Order property in both the request and response objects to mark the request/response ordering:

public List<WbsResponse> GetWbsResults()    
{        
    List<WbsRequest> requests = CompileWbsRequests();
    List<WbsResponse> results = new List<WbsResponse>();

    Parallel.ForEach(requests, (request) => {
        var response = CallWebService(request);
        response.Order = request.Order;
        results.Add(response);
    });

    results = results.OrderBy(r => r.Order).ToList();

    //do something with results

    return results;
}

private WbsResponse CallWebService(WbsRequest request)
{
    //Call web service
}

Edit/Update 2: Based on this thread, i've made a few changes to Update 1:

await Task.Run(() => {
    Parallel.ForEach(requests, (request) => {
        var response = CallWebService(request);
        response.Order = request.Order;
        results.Add(response);
    });
});

Requirement Summary:

Make multiple web service requests asynchronously to the same endpoint with different parameters.
Add web service results to a list in the same order as the request was made (as if it was synchronous).

Antoine V · Accepted Answer · 2018-07-06T08:39:08.900

1

Because each task finish with diffrent moment, I think you should numero the request and ordered the responses by this numero.

In the request, you init a numero and pass this numero for the response associated. Finally, when I have the results, I order it. Like this:

    public async Task<List<WbsResponse>> GetWbsResults()
    {
        List<WbsRequest> requests = CompileWbsRequests();
        List<Task<WbsResponse>> tasks = new List<Task<WbsResponse>>();
        for (var i = 0; i < requests.Count; i++)
        {
            var task = new Task<WbsResponse>(() => { CallWebService(WbsRequest); });
            tasks.Add(task);
        }
        var responses = await Task.WhenAll(tasks);

        var responsesOrdered = responses.OrderBy(r => r.Order)

        //do something with results

        return results;
    }  



    public List<WbsRequest> CompileWbsRequests()
    {
        //create requests
        foreach(var request in requests)
        {
            request.Order += 1;
        }
    }


    private WbsResponse CallWebService(WbsRequest request)
    {
        //Call web service

        reponse.order = request.order;
        return reponse;
    }

edited Jul 06 '18 at 08:39

answered Jul 06 '18 at 07:53

Antoine V

6,998
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You cannot use await without async – Sir Rufo Jul 06 '18 at 08:15
@SirRufo : Thanks for your comment. I updated the answer. – Antoine V Jul 06 '18 at 08:16
My C# compiler only accepts `async void` or `async Task` or `async Task<>` - maybe you have a special one – Sir Rufo Jul 06 '18 at 08:19
@SirRufo non, you were totally right, it should always async because I wrote the code directly on StackOverflow without a compiler with juste the idea how to work. I missed async, it's my mistake :) – Antoine V Jul 06 '18 at 08:21
`async List` will never compile but `async Task>` would – Sir Rufo Jul 06 '18 at 08:37
@ThierryV i've updated my question with a sample code based on your code. It looks cleaner than the `Task` based code. However, i'm not sure if this is efficient. – Sang Suantak Jul 06 '18 at 10:00
@SangSuantak I believe that it should work because ``Task.WhenAll(tasks)`` gives you an array of all task executed. With a simple order by, the results should be in order. – Antoine V Jul 06 '18 at 10:03
@ThierryV, i've made further updates to my question based on another source. Will accept your answer since it pointed me to the right direction. – Sang Suantak Jul 06 '18 at 10:15

Rey · Answer 2 · 2018-07-06T07:34:14.497

0

I think you can use Task.WaitAll to make the code work in async way and it will look prettier as well:

public List<WbsResponse> GetWbsResults()
{
    List<WbsRequest> requests = CompileWbsRequests();
    var responses = await Task.WhenAll(requests.Select(CallWebService));
    return responses;
}

but you have to modify this method as below to return a task:

private async Task<WbsResponse> CallWebService(WbsRequest request)
{
    //Call web service
}

edited Jul 06 '18 at 07:34

answered Jul 06 '18 at 07:21

Rey

3,663
3
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1

This will never compile – Sir Rufo Jul 06 '18 at 07:31
@SirRufo forgot to change the other method, now I think its compiled even thought i did not try it yet – Rey Jul 06 '18 at 07:34
2

This doesn't ensure ordered results as the WhenAll just runs all the tasks in parallel – Ulbo Jul 06 '18 at 07:38
Nope, it still will never compile – Sir Rufo Jul 06 '18 at 08:13
Thanks for the response @RajmondBurgaj, but if it doesn't return results in order like Ulbo said, it would not solve my problem. – Sang Suantak Jul 06 '18 at 09:00

Asynchronous multiple Web Service requests with ordered result

2 Answers2