public void completeEvent(int token) {
        if (token == this.barrierToken) {
            --eventCount;
            return;
        }
        --queue.get(queue.size() - (this.barrierToken - token)).eventCount;
        while (!queue.isEmpty() && queue.get(0).eventCount == 0) {
            queue.remove(0).handler.completeBarrier();
        }
    }
Signal the completion of an event. The value passed to this
method must be the same as the return value previously obtained
from the startEvent method. This method will signal the
completion of all pending barriers that were completed by the
completion of this event.

@param token Opaque token identifying the completed event.
vespajlib/src/main/java/com/yahoo/concurrent/EventBarrier.java