Actual Behavior

The current implementation uses separate goroutines to process each message retrieved by sqsClient.ReceiveMessageWithContext, which is executed when concurrencyMode is set to parallel. The consumeSubscription function waits for all spawned goroutines to complete before receiving the next batch. However, this design has a critical flaw: it starves the consumer if new messages are published during the processing of an existing batch. These newly published messages won't be processed until all goroutines from the original batch have finished their work, effectively blocking the consumption of the new messages.

Expected Behavior

Message handling should not be block until the batch is completely processed.

Steps to Reproduce the Problem

• Set a handler that blocks for a long time.
• Publish one sns message.
• Message will be handled.
• Publish another message
• Message will not be handled until the first finishes.