private boolean dispatchFirst() {
        Operation operation = operations.poll();
        if (operation == null)
            return false;

        if (operation.dispatch()) {
            enqueued.decrementAndGet();
            return true;
        }
        operations.push(operation);
        return false;
    }
Attempts to dispatch the first enqueued operations, and returns whether this was successful.
vespaclient-container-plugin/src/main/java/com/yahoo/document/restapi/resource/DocumentV1ApiHandler.java