[Design] Limit the Request per Second - Shuatiblog.com

[Design] Limit the Request per Second - Shuatiblog.com

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有一个接口叫 void setRPS(int num);
接下来不断有request过来，如何实现下面的接口，返回accept或者deny，

maintain a variable for the number of request processed/rejected.

1. This variable must be atomic, thus a AtomicInteger.
2. the variable is called 'count'

have a method to process request

1. if count < limit, do it
2. otherwise, reject

This is the most important: clear the count every 1 seconds!

1. eg. LIMIT = 5r/s, so:
2. the first 5 number of requests in every second are getting fulfilled
3. from 6th request onward, the request all rejected, until the next second.

public class SetRps {

    AtomicInteger count = new AtomicInteger(0);
    int limit = -1;
    int printIndex = 1;
    long startTimestamp = -1;

    void setRPS(int num) {
        limit = num;
    }

    boolean process(long timestamp) {
        // suppose timestamp is ms
        synchronized (this) {
            if (timestamp - startTimestamp >= 1000) {
                // every 1 seconds, reset
                count.set(0);
                startTimestamp = timestamp;
                System.out.println("clear!");
                return true;
            }      
            if (count.get() < limit) {
                // can process
                count.incrementAndGet();
                System.out.println(printIndex++ + ". processing request "
                        + timestamp % 100000 / 1000 + "," + timestamp % 1000);
                return true;
            }
        }
        return false;
    }
}
Google的Guava里提供了一个RateLimiter的class,可以做参考
Google Guava RateLimiter

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