Fix to main loop timeout calculation (#4671)

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

@@ -7,6 +7,8 @@ librdkafka v2.3.1 is a maintenance release:
  * Integration tests can be started in KRaft mode and run against any
    GitHub Kafka branch other than the released versions.
  * Fix pipeline inclusion of static binaries (#4666)
+ * Fix to main loop timeout calculation leading to a tight loop for a
+   max period of 1 ms (#4671).
 
 
 ## Fixes
@@ -20,6 +22,10 @@ librdkafka v2.3.1 is a maintenance release:
    Solved by correctly excluding the binary configured with that library,
    when targeting a static build.
    Happening since v2.0.2, with specified platforms, when using static binaries (#4666).
+ * 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

@@ -2120,7 +2120,10 @@ 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);