异步循环调用的异步方法的任何好处

Question

I'm writing a program that must pull data from an external api via an SDK. I'm not well versed in await/async operations - but know the SDK for each of the calls offers an Async method. GetResultsAsync<TObject>()

Each query has a limit of records returned - so in order to get all records for the month - I must order by ID, and loop. Here's some sample code of the current Synchronous calls out. As long as I get results - I check for more.

public List<TimeEntry> ListTimeEntries(DateTime startDate, DateTime endDate)
{
    var page = 1;
    var hasMore = false;
    var qry = string.Format("timeStart >= [{0}] and timeEnd <= [{1}]", startDate, endDate); //For example
    var results = List<TimeEntry>();
    do
    {
        var newItems = api.GetEntries(qry, "id desc", maxPageSize, page).GetResults<List<TimeEntry>>();
        results.AddRange(newItems);
        hasMore = newItems.Any();
        page++;
    } while (hasMore);
    return results;
}

This could make up to say 4-5 loops (or more depending on dates), but is obviously time consuming.

If I simply convert this to an async method - would I be able to have other synchronous calls being made at the same time? Let's assume I also need to get Service Tickets and Project Tickets for the same time period - but don't do any logical processing until all are returned. Could I have all three calls running asynchronously?

Here's the Goal

var startDate = DateTime.Now.AddDays(-30);
var endDate = DateTime.Now;

var timeTask = ListTimeEntries(startDate, endDate);
var serviceTask = ListServiceTickets(startDate, endDate);
var projectTask = ListProjectTickets(startdDate, endDate);

var timeEntries = await timeTask;
var serviceTickets = await serviceTask;
var projectTickets = await projectTask;

// Do what ever processing logic I need now.

How to Achieve?

For example #1 - would simply making the Method as async work? EG:

public async Task<List<TimeEntry>> ListTimeEntries(DateTime startDate, DateTime endDate)
{
    var page = 1;
    var hasMore = false;
    var qry = string.Format("timeStart >= [{0}] and timeEnd <= [{1}]", startDate, endDate); //For example
    var results = List<TimeEntry>();
    do
    {
        var newItems = api.GetEntries(qry, "id desc", maxPageSize, page).GetResults<List<TimeEntry>>();
        results.AddRange(newItems);
        hasMore = newItems.Any();
        page++;
    } while (hasMore);
    return results;
}

Or would there be any benefit for actually using the SDK's GetResultsAsync<> method such as Example 2 :

public async Task<List<TimeEntry>> ListTimeEntries(DateTime startDate, DateTime endDate)
{
    var page = 1;
    var hasMore = false;
    var qry = string.Format("timeStart >= [{0}] and timeEnd <= [{1}]", startDate, endDate); //For example
    var results = List<TimeEntry>();
    do
    {
        var newItemsTask = api.GetEntries(qry, "id desc", maxPageSize, page).GetResultsAsync<List<TimeEntry>>();
        var newItems = await newItemsTask;
        results.AddRange(newItems);
        hasMore = newItems.Any();
        page++;
    } while (hasMore);
    return results;
}

While I understand that these methods internally are still running Synchronously - I'm hoping to make each call to ListTimeEntries , ListServiceTickets , and ListProjectTickets happen asynchronously to speed up.

I guess my thought/hope - with lack of knowledge - would be that each Synchronous call would utilize a different thread - thus speeding up the overall process. Am I way off base?

Answer 1

I'd do something like the following. You will need to be aware of potential issues around API limits and of course there is the possibility for having at least three additional requests in-flight before all 4 threads complete - a small price to pay if you have lots of pages to retrieve.

public async Task<IList<TimeEntry>> CallSomething(DateTime startDate, DateTime endDate)
{
    var qry = string.Format("timeStart >= [{0}] and timeEnd <= [{1}]", startDate, endDate); //For example

    const threadCount = 4;

    var isComplete = new ManualResetEvent();
    var page = 0;
    var results = new ConcurrentBag<TimeEntry>();
    var thread = new Task[threadCount];
    for(var i = 0; i < threadCount; ++i)
    {
        thread[i] = Task.Run(
            async () =>
            {
                while(!isComplete.WaitOne(TimeSpan.Zero))
                {
                    var localPage = Interlocked.Increment(ref page);

                    var newItems = await api
                        .GetEntries(qry, "id desc", maxPageSize, localPage)
                        .GetResultsAsync<List<TimeEntry>>()
                        .ConfigureAwait(false);

                    if (!newItems.Any())
                    {
                        isComplete.Set();
                    }
                    else
                    {
                        foreach (var item in newItems)
                        {
                            results.Add(item);
                        }
                    }
                }
            })
        )
    }

    await Task.WhenAll(thread).ConfigureAwait(false);

    return results.OrderByDescending(f => f.Id).ToList();
}