How to manage a series of PATCH calls to Azure DevOps REST API to avoid HTTP Response Conflict error 409

In a custom C# Winforms app, I'm using the Azure DevOps REST API Update Comments call to update work item comments using async/await

My call to UpdateComment_Async is in a tight loop designed to submit all update comment requests for a single work item and then process each comment update as it completes.

Following is a mix of p-code and C# for (almost) working code. In the case where there are 2 (or more) comments to update, the first update returns HttpResponseMessage.Status 200 (success), but the second update submitted returns HttpResponseMessage.Status 409 "Conflict". I assume that ADS has the work item locked for the first update, and so the 2nd update fails with the 409. I think I proved this by sleeping the thread for 5 seconds after the call to UpdateComment_Async. With the sleep in place, both updates work.

Is there a way to manage the series of calls to UpdateComment_Async so that subsequent calls aren't done until the previous one is complete?

CODE

// get comment(s) for one work item .......

foreach (comment in workItem)
{
    newCommentText = "new comment text blah-blah-blah";

    Task<Tuple<string, string, HttpResponseMessage>> updateCommentTask = UpdateComment_Async(projectUrl, workItem.Id.ToString(), comment.Id.ToString(), newCommentText);
    
    // I put a thread.sleep(5000) right here

    updateCommentTaskList.Add(updateCommentTask);
}

// Process update comments tasks as they complete
while (updateCommentTaskList.Count > 0)
{
    Task<Tuple<string, string, HttpResponseMessage>> finishedUpdateCommentTask = await Task.WhenAny(updateCommentTaskList);

    // Get Results
    Tuple<string, string, HttpResponseMessage> updateCommentTaskResult = finishedUpdateCommentTask.Result;

    // process updateCommentTaskResult
    // etc
    // etc
    // etc
    
    updateCommentTaskList.Remove(finishedUpdateCommentTask);
}

//*******************************

public async Task<Tuple<string, string, HttpResponseMessage>> UpdateComment_Async(string projectUrl, string workItemId, string commentId, string commentNumber, string newCommentText)
{
    HttpResponseMessage responseResult = null;

    #region MAKE JSON REQUEST BODY

    IList<ClsUpdateComment> updateFieldJsonList = new List<ClsUpdateComment>();
    updateFieldJsonList.Clear();

    // Note: This code works but is not in compliance with MS docs on 2 counts.
    //
    // 1) The MS docs on comment update say that the body should look like fig 1.
    // The only I could do this was to create a new ClsUpdateComment and then add it to  
    // List<ClsUpdateComment>. Adding the ClsUpdateComment object to a list causes the [ ] 
    // to be created when the list is serialized. To make this work, I had to serialize
    // just the ClsUpdateComment object so that when serialzed, it ends up looking like Fig 2 (no brackets)
    //
    // 2) application/json-patch+json causes error 415 - unsupported media type to occur. application/json
    // works.

    /*
    Fig 1

    [
        {
            "text": "Moving to the right area path - Fabrikam-Git"
        }
    ]

    Fig 2

    {
        "text": "Moving to the right area path - Fabrikam-Git"
    }

    */

    ClsUpdateComment updateFieldJson = new ClsUpdateComment
    {
        Text = $"{newCommentText}"
    };

    updateFieldJsonList.Add(updateFieldJson);

    #endregion MAKE JSON REQUEST BODY

    #region SUBMIT UPDATE REQUEST

    string request = $"{projectUrl}/_apis/wit/workitems/{workItemId}/comments/{commentId}?api-version=5.1-preview.3";

    JsonSerializerSettings jsonSerializerSettings = new JsonSerializerSettings
    {
        StringEscapeHandling = StringEscapeHandling.EscapeHtml,
    };

    string updateFieldJsonSerialized = JsonConvert.SerializeObject(updateFieldJson, Formatting.None, jsonSerializerSettings);

    using (HttpClient client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true, ClientCertificateOptions = ClientCertificateOption.Manual }))
    {
        client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));

        HttpRequestMessage httpRequestMessage = new HttpRequestMessage(new HttpMethod("PATCH"), request)
        {
            Content = new StringContent(updateFieldJsonSerialized, Encoding.UTF8, "application/json")
        };

        using (responseResult = await client.SendAsync(httpRequestMessage))
        {
            // don't need Content, just the HttpResponseMessage
            // //string content = await responseResult.Content.ReadAsStringAsync();
        }
    }

    #endregion SUBMIT UPDATE REQUEST

    return Tuple.Create(workItemId, commentNumber, responseResult);
}