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 +1,81 @@
+#include "ucore/rate_limit.h"
+
+#define SCALE_FACTOR 1000
+
+
+void uc_ratelimit_init(struct RateLimit *r, long tickets, long period, long current_ts)
+{
+    r->tickets = tickets;
+    r->scaled_tickets = tickets * SCALE_FACTOR;
+    r->period = period;
+    r->available_tickets = r->scaled_tickets;
+    r->last_ts = current_ts;
+}
+
+void uc_ratelimit_reset(struct RateLimit *r, long current_ts)
+{
+    r->available_tickets = r->scaled_tickets;
+
+    if (current_ts)
+        r->last_ts = current_ts;
+}
+
+int uc_ratelimit_allow(struct RateLimit *r, long current_ts)
+{
+    int allowed;
+    long diff_period;
+
+    //Find elapsed time
+    diff_period = current_ts - r->last_ts;
+
+    //If time went backwards, we halt the time for this round
+    if (diff_period < 0) 
+        diff_period = 0;
+
+    //Calculate the number of tickets that became available since 
+    //the last time. (+ ScALE_FACTOR/2 is to round up at halfway points for
+    //integer arithmetics)
+    r->available_tickets += diff_period  * 
+                            ((r->scaled_tickets + SCALE_FACTOR/2) / r->period);
+
+    //throttle handing out tickets
+    //
+    if (r->available_tickets > r->scaled_tickets) 
+        r->available_tickets = r->scaled_tickets;
+
+    //If we have at least onen ticket, we can allow 
+    if (r->available_tickets >=  1 * SCALE_FACTOR) {
+        r->available_tickets -= 1 * SCALE_FACTOR;
+        allowed = 1;
+    } else {
+        //no more tickets.
+        allowed = 0;
+    }
+
+    //save this period. 
+    r->last_ts = current_ts;
+
+    return allowed;
+}
+
+#if 0
+int main()
+{
+    int i;
+    struct RateLimit r;
+    time_t start;
+
+    uc_ratelimit_init(&r, 10, 60, time(NULL));
+
+    for(i = 0; i < 120; i++) {
+        int k;
+        long allowed = 0;
+        sleep(1);
+        for (k = 0; k < 500; k++) 
+            allowed += uc_ratelimit_allow(&r, time(NULL));
+        printf("%ld of 500 can pass\n", allowed);
+    }
+
+    return 0;
+}
+#endif