Add rate limit API

2013-10-09 22:55:29 +02:00
parent 08a50d8cfe
commit 06083a054e
2 changed files with 151 additions and 0 deletions
@@ -0,0 +1,70 @@
+#ifndef UC_RATE_LIMIT_H_
+#define UC_RATE_LIMIT_H_
+
+/** This is a rate limiter, based on the token bucket principle.
+ * We have X amount of tickets(=our rate) per Y amount of time,
+ *  
+ * The allowed tickets increases with X per Y amount of time.
+ * 
+ * Bursts will be allowed up till the number of tickets initially
+ * specified.
+ * e.g. if we are limited to 50 tickets * per 2 second, 50 tickets 
+ * can be immedietely handed out in the
+ * first second. At the 2. second, 25 more tickets become available
+ * handed out, at the 3. second 25 more, and so on. 
+ * (So this is throttleed, so no more than the initial tickets, 50 in 
+ * this case, can be handed out in any given period)
+ *
+ * Another example is if we rate 1000 tickets per 60 seconds,
+ * 1000 tickets can be handed out the 1. second, 16/17 more the 
+ * next second, 16/17 more the 3. second and so on.
+ *
+ * Specify how many tickes we have available per period of time.
+ * when work is performed, call uc_ratelimit_cllow() with the current
+ * time. 
+ * The unit of time passed to uc_ratelimit_allow must be the same as 
+ * for uc_ratelimit_init.
+ *
+ * Example for rate limiting accepting connections:
+ * struct RateLimit r;
+ * //Limit to 20 per 1 second, which also limits us to max 20 
+ * per second. (1 second since we will pass in time that have 1 second resolution)
+ * 40 per 2 second would even out to the same rate, but allow a burst of 40
+ * (if there's 40 tickets available)
+ *
+ * uc_ratelimit_init(&r,20, 1, time(NULL));
+ *
+ * for (;;) {
+ *    int fd = accept(..);
+ *    if (uc_ratelimit_allow(&r, time(NULL)) {
+ *       //handle new connection
+ *    } else {
+ *      //exceeded limit
+ *      close(fd);
+ *    }
+ *  }
+ */
+struct RateLimit {
+    //how many tickets we want
+    long tickets;
+    //per this period of time
+    long period;
+
+    //internal fields:
+
+    //scaled up number of tickets, to avoid floating point
+    //math
+    long scaled_tickets;
+
+    //number of tickets we have (scaled up)
+    long available_tickets;
+    //time of the previos period
+    long last_ts;
+};
+
+void uc_ratelimit_init(struct RateLimit *r, long tickets, long period, long current_ts);
+void uc_ratelimit_reset(struct RateLimit *r, long current_ts);
+int uc_ratelimit_allow(struct RateLimit *r, long current_ts);
+
+#endif
+