guava/src/com/google/common/util/concurrent/RateLimiter.java
public boolean tryAcquire(int permits, long timeout, TimeUnit unit) {
    long timeoutMicros = max(unit.toMicros(timeout), 0);
    checkPermits(permits);
    long microsToWait;
    synchronized (mutex()) {
      long nowMicros = stopwatch.readMicros();
      if (!canAcquire(nowMicros, timeoutMicros)) {
        return false;
      } else {
        microsToWait = reserveAndGetWaitLength(permits, nowMicros);
      }
    }
    stopwatch.sleepMicrosUninterruptibly(microsToWait);
    return true;
  }
public boolean tryAcquire(int permits, long timeout, TimeUnit unit) {
    long timeoutMicros = max(unit.toMicros(timeout), 0);
    checkPermits(permits);
    long microsToWait;
    synchronized (mutex()) {
      long nowMicros = stopwatch.readMicros();
      if (!canAcquire(nowMicros, timeoutMicros)) {
        return false;
      } else {
        microsToWait = reserveAndGetWaitLength(permits, nowMicros);
      }
    }
    stopwatch.sleepMicrosUninterruptibly(microsToWait);
    return true;
  }
public boolean tryAcquire ( int permits , long timeout , TimeUnit unit ) { long timeoutMicros = max ( unit . toMicros ( timeout ) , 0 ) ; checkPermits ( permits ) ; long microsToWait ; synchronized ( mutex ( ) ) { long nowMicros = stopwatch . readMicros ( ) ; if ( ! canAcquire ( nowMicros , timeoutMicros ) ) { return false ; } else { microsToWait = reserveAndGetWaitLength ( permits , nowMicros ) ; } } stopwatch . sleepMicrosUninterruptibly ( microsToWait ) ; return true ; }
Acquires the given number of permits from this {@code RateLimiter} if it can be obtained
without exceeding the specified {@code timeout}, or returns {@code false} immediately (without
waiting) if the permits would not have been granted before the timeout expired.

@param permits the number of permits to acquire
@param timeout the maximum time to wait for the permits. Negative values are treated as zero.
@param unit the time unit of the timeout argument
@return {@code true} if the permits were acquired, {@code false} otherwise
@throws IllegalArgumentException if the requested number of permits is negative or zero
Acquires the given number of permits from this { @code RateLimiter } if it can be obtained without exceeding the specified { @code timeout } or returns { @code false } immediately ( without waiting ) if the permits would not have been granted before the timeout expired .