计数器

public class LatencyTracker {

    private final AtomicLong opCount = new AtomicLong(0);
    private final AtomicLong totalLatency = new AtomicLong(0);
    private long lastLatency = 0;
    private long lastOpCount = 0;

    /**
     * takes nanoseconds *
     */
    public void addNano(long nanos) {
        // convert to microseconds.  1 millionth
        addMicro(nanos / 1000);
    }

    public void addMicro(long micros) {
        opCount.incrementAndGet();
        totalLatency.addAndGet(micros);
    }

    public long getOpCount() {
        return opCount.get();
    }

    /**
     * returns microseconds
     */
    public long getTotalLatencyMicros() {
        return totalLatency.get();
    }

    /**
     * returns microseconds
     */
    public double getRecentLatencyMicros() {
        long ops = opCount.get();
        long n = totalLatency.get();
        try {
            return ((double) n - lastLatency) / (ops - lastOpCount);
        } finally {
            lastLatency = n;
            lastOpCount = ops;
        }
    }

    @Override
    public String toString() {
        long average = totalLatency.get() / (opCount.get() + 1);
        return "LatencyTracker{" + "opCount=" + opCount + ", totalLatency=" + totalLatency + ", averageLatency=" + average + "}";
    }
}