[BUG] Azure Search: Deadlock searching for documents with DocumentsOperationsExtensions.Search()

[tomillie]

Describe the bug
We've upgraded our existing Azure Search implementation to use the newest 9.0.0 version of .NET SDK, resolved all breaking changes, but the synchronous search methods seem to deadlock.

Stack Trace

mscorlib.dll!System.Threading.ManualResetEventSlim.Wait(int millisecondsTimeout = -1, System.Threading.CancellationToken cancellationToken)
mscorlib.dll!System.Threading.Tasks.Task.SpinThenBlockingWait(int millisecondsTimeout, System.Threading.CancellationToken cancellationToken)
mscorlib.dll!System.Threading.Tasks.Task.InternalWait(int millisecondsTimeout = -1, System.Threading.CancellationToken cancellationToken)
mscorlib.dll!System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(System.Threading.Tasks.Task task = Id = 2351, Status = WaitingForActivation, Method = "{null}", Result = "{Not yet computed}")
Microsoft.Azure.Search.Data.dll!Microsoft.Azure.Search.DocumentsOperationsExtensions.Search(Microsoft.Azure.Search.IDocumentsOperations operations, string searchText, Microsoft.Azure.Search.Models.SearchParameters searchParameters, Microsoft.Azure.Search.Models.SearchRequestOptions searchRequestOptions)
CMSApp.dll!CMSWebParts_DancingGoat_Samples_DancingGoatSmartSearchAzure.Page_Load(object sender = CMSAbstractWebPart("SampleDancingGoat_SmartSearchAzure"), System.EventArgs e = {System.EventArgs})
....

Code Snippet

result = searchIndexClient.Documents.Search(searchString, searchParams);

It seems the following code in DocumentsOperationsExtensions.cs is missing a ConfigureAwait(false) before synchronously waiting for the result.

public static DocumentSearchResult<Document> Search(
            this IDocumentsOperations operations,
            string searchText,
            SearchParameters searchParameters = null,
            SearchRequestOptions searchRequestOptions = default(SearchRequestOptions))
        {
            return operations.SearchAsync(searchText, searchParameters, searchRequestOptions).GetAwaiter().GetResult();
}

Similar methods possibly with the same issue:
Microsoft.Azure.Search.DocumentsOperationsExtensions.Search(...)
Microsoft.Azure.Search.DocumentsOperationsExtensions.Search\<T\>(...)
Microsoft.Azure.Search.DocumentsOperationsExtensions.Count(...)
Microsoft.Azure.Search.DocumentsOperationsExtensions.Autocomplete(...)
etc.

Expected behavior
No deadlock. Synchronous search is possible.

Setup (please complete the following information):

• Azure Search .NET SDK version 9

Additional context
I can see the JSON response in Fiddler, but the method doesn't return anything.

Information Checklist
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[brjohnstmsft]

Thanks for reporting this. We're aware of the issue and are looking into it.

[brjohnstmsft]

@tomillie The code you pointed out hasn't changed since 5.0.3. There is a missing ConfigureAwait(false), but I don't think it's there.

I have a few questions that will help confirm my hypothesis:

1. Can you confirm whether the other methods block too, or is it only Search?
2. If you set UseHttpGetForQueries to true, does the issue go away?

[tomillie]

Hi, sorry for the delay...

1. I tried the methods I mentioned in the first comment and they don't deadlock. So it seems only Search() is affected.
2. Yes, that helped.

By the way, we had no problem with the version 5.0.3, only 9.0.0 seems faulty.

[brjohnstmsft]

@tomillie Thanks for confirming. I have a PR out for the fix and I hope to be able to push it to NuGet today.

[brjohnstmsft]

Version 9.0.1, which includes this fix, is now available on NuGet.