Azure Service Bus Queue: How the ordering of the message work? - azure

Question

public static async Task DoMessage()
{
const int numberOfMessages = 10;
queueClient = new QueueClient(ConnectionString, QueueName);
await SendMessageAsync(numberOfMessages);
await queueClient.CloseAsync();
}
private static async Task SendMessageAsync(int numOfMessages)
{
try
{
for (var i = 0; i < numOfMessages; i++)
{
var messageBody = $"Message {i}";
var message = new Message(Encoding.UTF8.GetBytes(messageBody));
message.SessionId = i.ToString();
await queueClient.SendAsync(message);
}
}
catch (Exception e)
{
}
}
This is my sample code to send message to the service bus queue with session id.
My question is if I call DoMessage function 2 times: Let's name it as MessageSet1 and MessageSet2, respectively. Will the MessageSet2 be received and processed by the received azure function who dealing with the receiving ends of the message.
I want to handle in order like MessageSet1 then the MessageSet2 and never handle with MessageSet2 unless MessageSet1 finished.

Answer 1

There are a couple of issues with what you're doing.
First, Azure Functions do not currently support sessions. There's an issue for that you can track.
Second, the sessions you're creating are off. A session should be applied on a set of messages using the same SessionId. Meaning your for loop should be assigning the same SessionId to all the messages in the set. Something like this:
private static async Task SendMessageAsync(int numOfMessages, string sessionID)
{
try
{
var tasks = new List<Task>();
for (var i = 0; i < numOfMessages; i++)
{
var messageBody = $"Message {i}";
var message = new Message(Encoding.UTF8.GetBytes(messageBody));
message.SessionId = sessionId;
tasks.Add(queueClient.SendAsync(message));
}
await Task.WhenAll(tasks).ConfigureAwait(false);
}
catch (Exception e)
{
// handle exception
}
}
For ordered messages using Sessions, see documentation here.