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SQS Queue Poller

A pair of console applications demonstrating Amazon SQS message passing. Also the only non-GUI sample in the collection, if you want to see the SDK outside of a desktop app.

The Poller uses TSQSQueuePoller to efficiently receive messages from a queue. The Sender uses TSQSClient.SendMessage to push messages onto it.

What's demonstrated

  • TSQSQueuePoller for long-polling (no manual receive loops needed)
  • TSQSClient.SendMessage for pushing messages
  • TSQSQueuePollerStatistics for request count and received message count
  • Configurable batch size, up to 10 messages per receive
// Poller — three lines to start consuming messages
QueuePoller := TSQSQueuePoller.Create(QueueURL);
QueuePoller.Poll(
  procedure(const AMessages: TSQSMessages)
  begin
    for var LMessage in AMessages do
      WriteLn('Received: ', LMessage.Body);
  end
);
// Sender — one line per message
SQS := TSQSClient.Create;
SQS.SendMessage(QueueURL, 'Order #1234 ready for processing');

Running the sample

  1. Create a queue in the Simple Queue Service Console and take note of the Queue URL.
  2. Open the "SQS Queue Poller.groupproj" project group in Delphi or RAD Studio.
  3. Build all applications using the "Project > Build All Projects" menu item.
  4. Launch two instances of cmd.exe and place them side-by-side so you can see the results.
  5. Change directory into the project output folder (e.g. Win32\Debug) in both command shells.
  6. In the first command shell, run the poller (replace the URL with your Queue URL from step 1): Poller.exe https://sqs.eu-west-1.amazonaws.com/123456789012/MyQueue
  7. In the second command shell, run the sender: Sender.exe Sender1 https://sqs.eu-west-1.amazonaws.com/123456789012/MyQueue

Receiving batches of messages

In a real-world scenario, you'll likely want to receive batches of messages for processing. By default, TSQSQueuePoller fetches one message per batch, but you can specify the upper limit of the batch size (up to 10). To demonstrate this, uncomment the line QueuePoller.MaxNumberOfMessages := 3; in Poller.dpr and recompile.

Once you have restarted the Poller as per the previous instructions, you can run multiple instances of Sender.exe to push more messages into the queue simultaneously. The second argument to Sender.exe is a name to identify the instance of the sender, so set each instance to a unique name (e.g. "Sender1", "Sender2"). Once the queue has enough messages being delivered, you will start to see the Poller output batched:

[20220513T152808] Messages received to date 10
[20220513T152808] Received message: Message 104 from Sender1
[20220513T152808] Received message: Message 105 from Sender2
[20220513T152808] Received message: Message 113 from Sender1
[20220513T152808] Polling iteration 5
[20220513T152808] Messages received to date 13
[20220513T152808] Received message: Message 102 from Sender1
[20220513T152808] Received message: Message 112 from Sender1

Required IAM permissions

Poller:

  • sqs:ReceiveMessage
  • sqs:DeleteMessage
  • sqs:GetQueueAttributes

Sender:

  • sqs:SendMessage