protected void onRequestAdded(R request) {
            // to be overridden by subclasses
        }
A hook to be run when a request is successfully added to this buffer. Called by
{@code addIfAllowed} with a lock on {@code this} held.

@param request
           the request that was added
aws-java-sdk-sqs/src/main/java/com/amazonaws/services/sqs/buffered/SendQueueBuffer.java