private static RateLimiter one=RateLimiter.create(2);//每秒2个
  private static RateLimiter two=RateLimiter.create(2);//每秒2个
  private RateLimitUtil(){};
  public static void acquire(RateLimiter r,int num){
    double time =r.acquire(num);
    System.out.println("wait time="+time);
  }
  public static void main(String[] args) throws InterruptedException {
    acquire(one,1);
    acquire(one,1);
    acquire(one,1);
    System.out.println("-----");
    acquire(two,10);
    acquire(two,1);
  }

wait time=0.0
wait time=0.499163
wait time=0.489308
-----
wait time=0.0
wait time=4.497819

public double acquire(int permits) {
  long microsToWait = reserve(permits);//先计算获取这些请求需要让线程等待多长时间
  stopwatch.sleepMicrosUninterruptibly(microsToWait);//让线程阻塞microTowait微秒长的时间
  return 1.0 * microsToWait / SECONDS.toMicros(1L);//返回阻塞的时间
 }

final long reserve(int permits) {
  checkPermits(permits);//检查参数是否合法
  synchronized (mutex()) {
   return reserveAndGetWaitLength(permits, stopwatch.readMicros());
  }
 }
    ↓
    ↓
    ↓
 final long reserveAndGetWaitLength(int permits, long nowMicros) {
  long momentAvailable = reserveEarliestAvailable(permits, nowMicros);
  return max(momentAvailable - nowMicros, 0);
 }
    ↓
    ↓
    ↓
 final long reserveEarliestAvailable(int requiredPermits, long nowMicros) {
  resync(nowMicros);//here
  long returnValue = nextFreeTicketMicros;
  double storedPermitsToSpend = min(requiredPermits, this.storedPermits);
  double freshPermits = requiredPermits - storedPermitsToSpend;
  long waitMicros = storedPermitsToWaitTime(this.storedPermits, storedPermitsToSpend)
    + (long) (freshPermits * stableIntervalMicros);
  this.nextFreeTicketMicros = nextFreeTicketMicros + waitMicros;
  this.storedPermits -= storedPermitsToSpend;
  return returnValue;
 }

private void resync(long nowMicros) {
  // if nextFreeTicket is in the past, resync to now
  if (nowMicros > nextFreeTicketMicros) {
   storedPermits = min(maxPermits,
     storedPermits + (nowMicros - nextFreeTicketMicros) / stableIntervalMicros);
   nextFreeTicketMicros = nowMicros;
  }
 }

final long reserveEarliestAvailable(int requiredPermits, long nowMicros) { //1
  resync(nowMicros);   //2
  long returnValue = nextFreeTicketMicros;//3
  double storedPermitsToSpend = min(requiredPermits, this.storedPermits);//4
  double freshPermits = requiredPermits - storedPermitsToSpend;//5
  long waitMicros = storedPermitsToWaitTime(this.storedPermits, storedPermitsToSpend)
    + (long) (freshPermits * stableIntervalMicros);//6
  this.nextFreeTicketMicros = nextFreeTicketMicros + waitMicros;//7
  this.storedPermits -= storedPermitsToSpend;//8
  return returnValue;//9
 }

final long reserveAndGetWaitLength(int permits, long nowMicros) {
  long momentAvailable = reserveEarliestAvailable(permits, nowMicros);
  return max(momentAvailable - nowMicros, 0);//取较大的值
 }

public double acquire(int permits) {
  long microsToWait = reserve(permits);
  stopwatch.sleepMicrosUninterruptibly(microsToWait);
  return 1.0 * microsToWait / SECONDS.toMicros(1L);
 }

private static RateLimiter too=RateLimiter.create(2);//每秒2个
  private RateLimitUtil(){};
  public static void acquire(RateLimiter r,int num){
    double time =r.acquire(num);
    System.out.println("wait time="+time);
  }
  public static void main(String[] args) throws InterruptedException {
    acquire(too,1);
    acquire(too,10);//只等待了0.5秒就获取了10个
    acquire(too,10);//等待了5秒就获取了10个
    acquire(too,1);//虽然只获取1个，也是等待5秒
  }