当您尝试取消已排队的计划Azure服务总线消息时会发生什么？

Question

I'm trying to come up with the best way to schedule a message for an Azure service bus queue or topic while leaving the option open for immediately sending a message instead of the scheduled message. I want to make sure I can protect myself against creating a duplicate message if I try to send the replacement message right at or after the scheduled time of the first message.

What will happen if I try to cancel a scheduled message with CancelScheduledMessageAsync (for both QueueClient and TopicClient classes) after the message has already been enqueued? Will it throw an exception?

Answer 1

According to your description, I found a blog ( Canceling Scheduled Messages ) talking about the similar issue.

Before version 3.3.1, a scheduled message needs to be canceled prior to becoming visible, it was not possible . And any attempt to access its value would result in InvalidOperationException . Therefore, any messages scheduled in the future and no longer needed would be "stuck" on the broker until the later time.

With Microsoft Azure Service Bus >= 3.3.1 QueueClient or TopicClient can be used to schedule a message and cancel it later.

Also, I have tested it on my side via the following code:

BrokeredMessage brokerMsg= new BrokeredMessage("Hello World!!!");
long sequenceNumber = await queueClient.ScheduleMessageAsync(brokerMsg, DateTimeOffset.UtcNow.AddSeconds(30));

await Task.Delay(TimeSpan.FromMinutes(1));
// Cancel scheduled message
await queueClient.CancelScheduledMessageAsync(sequenceNumber);

I logged into azure portal and checked ACTIVE MESSAGE COUNT and SCHEDULED MESSAGE COUNT . I could cancel the scheduled message before it becomes active, but if I cancel the scheduled message via the sequenceNumber after the scheduled message becomes active, then I would retrieve the exception as follows: