protected boolean isFull() {
            return requests.size() >= config.getMaxBatchSize();
        }
Checks whether the buffer is now full. Called by {@code addIfAllowed} with a lock on
{@code this} held.

@return whether the buffer is filled to capacity
aws-java-sdk-sqs/src/main/java/com/amazonaws/services/sqs/buffered/SendQueueBuffer.java