How can I run 2 QueryFeaturesAsync in parallel ?

MarcHillman

Having just discovered ServiceFeatureTable I am now converting my code to use them. I have an opportunity to execute 2 queries in parallel, but I can't work out how to do it.

Code fragment 1 shows my Serial code. It works correctly.

 

        Dim sft_SA4 As New ServiceFeatureTable(New Uri($"{MAPSERVER_SA4}"))
        Dim sft_SA3 As New ServiceFeatureTable(New Uri($"{MAPSERVER_SA3}"))
        Dim myquery As New QueryParameters
        Dim fc1 As FeatureQueryResult, fc2 As FeatureQueryResult

        fc1 = Await sft_SA4.QueryFeaturesAsync(myquery).ConfigureAwait(False)
        fc2 = Await sft_SA3.QueryFeaturesAsync(myquery).ConfigureAwait(False)

 

Code fragment 2 shows my attempt to run both these queries in parallel. It compiles, but when run it just hangs at the WhenAll statement

Dim sft_SA4 As New ServiceFeatureTable(New Uri($"{MAPSERVER_SA4}"))
Dim sft_SA3 As New ServiceFeatureTable(New Uri($"{MAPSERVER_SA3}"))
Dim myquery As New QueryParameters
Dim fc1 As FeatureQueryResult, fc2 As FeatureQueryResult
Dim t1 = sft_SA4.QueryFeaturesAsync(myquery)
Dim t2 = sft_SA3.QueryFeaturesAsync(myquery)
Await Task.WhenAll(t1, t2)      ' both complete
fc1 = t1.Result
fc2 = t1.result

 What have I done wrong? (myquery is populated elsewhere, but left out for clarity)

MichaelBranscomb

Apologies. 

I just tried your code and it appear to work fine: control returns to the UI thread and the async tasks continue to run effectively in the background. For the query I'm using 1=1 which retrieves all features which appear to be about 100 per layer. Note it took almost 1min from submitting the query to the service responding so I do think the server/service appears to be running a little slowly.

 

string MAPSERVER_SA4 = "https://geo.abs.gov.au/arcgis/rest/services/ASGS2021/SA4/MapServer/0";
string MAPSERVER_SA3 = "https://geo.abs.gov.au/arcgis/rest/services/ASGS2021/SA4/MapServer/1";
ServiceFeatureTable sft_SA4 = new ServiceFeatureTable (new Uri($"{MAPSERVER_SA4}"));
ServiceFeatureTable sft_SA3 = new ServiceFeatureTable(new Uri($"{MAPSERVER_SA3}"));
QueryParameters myquery = new QueryParameters() { WhereClause="1=1"};
FeatureQueryResult fc1; FeatureQueryResult fc2;

var t1 = sft_SA4.QueryFeaturesAsync(myquery);
var t2 = sft_SA3.QueryFeaturesAsync(myquery);
await Task.WhenAll(t1, t2);    // both complete
fc1 = t1.Result;
fc2 = t1.Result;