Fix to main loop timeout calculation

leading to a tight loop for a max period of 1 ms

When the main thread loop was awakened less than 1 ms
before the expiration of a timeout, it was serving with a zero timeout,
leading to increased CPU usage until the timeout was reached.
Happening since 1.x

CHANGELOG.md

@@ -11,6 +11,8 @@ librdkafka v2.3.1 is a maintenance release:
    and updating the topic id corresponding to the partition name (#4660)
  * Fixes to metadata cache expiration, metadata refresh interruption and
    to avoid usage of stale metadata (#4660).
+ * Fix to main loop timeout calculation leading to a tight loop for a
+   max period of 1 ms (#4671).
 
 
 ## Fixes
@@ -32,6 +34,10 @@ librdkafka v2.3.1 is a maintenance release:
    was undergoing a validation and being retried because of an error.
    Solved by doing a partition migration only with a non-stale leader epoch.
    Happening since 2.1.0 (#4660).
+ * When the main thread loop was awakened less than 1 ms
+   before the expiration of a timeout, it was serving with a zero timeout,
+   leading to increased CPU usage until the timeout was reached.
+   Happening since 1.x (#4671).
 
 
 

src/rdkafka.c

@@ -2127,7 +2127,10 @@ static int rd_kafka_thread_main(void *arg) {
                                        RD_KAFKA_CGRP_STATE_TERM)))) {
                 rd_ts_t sleeptime = rd_kafka_timers_next(
                     &rk->rk_timers, 1000 * 1000 /*1s*/, 1 /*lock*/);
-                rd_kafka_q_serve(rk->rk_ops, (int)(sleeptime / 1000), 0,
+                /* Use ceiling division to avoid calling serve with a 0 ms
+                 * timeout in a tight loop until 1 ms has passed. */
+                int timeout_ms = (sleeptime + 999) / 1000;
+                rd_kafka_q_serve(rk->rk_ops, timeout_ms, 0,
                                  RD_KAFKA_Q_CB_CALLBACK, NULL, NULL);
                 if (rk->rk_cgrp) /* FIXME: move to timer-triggered */
                         rd_kafka_cgrp_serve(rk->rk_cgrp);