Leaky Bucket Algorithm

 
 /**
     * Leaky bucket algorithm to prevent huge amounts of SMS text messages
     * from being dispatched by any insane processes. Each SMS message
     * sent adds a drop to the
     * bucket which leaks at a constant rate. Once the bucket fills, no
     * message can be sent until a drop has leaked out.
     */
    private class LeakyBucketLimiter {

        private int numDropsInBucket = 0;
        private Date timeOfLastDropLeak = null;
        private final int _BUCKET_SIZE_IN_DROPS = 20;
        private final long _MS_BETWEEN_DROP_LEAKS = 1000 * 60 * 60; // 1 hour

        public synchronized boolean addDropToBucket() {
            Date now = new Date();
            // first of all, let the bucket leak by the appropriate amount
            if (timeOfLastDropLeak != null) {
                long deltaT = now.getTime() - timeOfLastDropLeak.getTime();
                // note round down as part of integer arithmetic
                long numberToLeak = deltaT / _MS_BETWEEN_DROP_LEAKS;
                if (numberToLeak > 0) { //now go and do the leak
                    if (numDropsInBucket <= numberToLeak) {
                        numDropsInBucket = 0;
                    } else {
                        numDropsInBucket -= (int) numberToLeak;
                    }
                    timeOfLastDropLeak = now;
                }
            }

            if (numDropsInBucket < _BUCKET_SIZE_IN_DROPS) {
                numDropsInBucket++;
                return true; // drop added
            }

            return false; // overflow
        }
    }


    // here is how you use it
    bucketLimiter = new LeakyBucketLimiter();
    if (bucketLimiter.addDropToBucket()) {
        // dispatch SMS
    }