synchronized boolean waitForZero() throws InterruptedException {
            while (value > 0) {
                wait();
            }
            return true;
        }
Implement replyHandler from messagebus. Called when a reply is received from messagebus.
Tries to find the callback from the reply context and updates the pending state for the callback.

@param r the reply to process.
vespaclient-core/src/main/java/com/yahoo/feedapi/SharedSender.java