ARTEMIS-2800 Work around (trapping) current race identified on a BZ
https://bugzilla.redhat.com/show_bug.cgi?id=1845326
diff --git a/src/main/c/org_apache_activemq_artemis_nativo_jlibaio_LibaioContext.c b/src/main/c/org_apache_activemq_artemis_nativo_jlibaio_LibaioContext.c
index e057311..d495eb4 100644
--- a/src/main/c/org_apache_activemq_artemis_nativo_jlibaio_LibaioContext.c
+++ b/src/main/c/org_apache_activemq_artemis_nativo_jlibaio_LibaioContext.c
@@ -149,6 +149,24 @@
if (!available) {
return 0;
}
+
+ if (available >= max) {
+ // This is to trap a possible bug from the kernel:
+ // https://bugzilla.redhat.com/show_bug.cgi?id=1845326
+ // https://issues.apache.org/jira/browse/ARTEMIS-2800
+ //
+ // On the race available would eventually be >= max, while ring->tail was invalid
+ // we could work around by waiting ring-tail to change:
+ // while (ring->tail == tail) mem_barrier();
+ //
+ // however eventually we could have available==max in a legal situation what could lead to infinite loop here
+ return io_getevents(aio_ctx, min_nr, max, events, timeout);
+
+ // also: I could have called io_getevents to the one at the end of this method
+ // but I really hate goto, so I would rather have a duplicate code here
+ // and I did not want to create another memory flag to stop the rest of the code
+ }
+
//the kernel has written ring->tail from an interrupt:
//we need to load acquire the completed events here
read_barrier();
@@ -177,6 +195,8 @@
fprintf(stdout, "The kernel is not supoprting the ring buffer any longer\n");
#endif
}
+ // if this next line ever needs to be changed, beware of a duplicate code on this method
+ // I explain why I duplicated the call instead of reuse it there ^^^^
int sys_call_events = io_getevents(aio_ctx, min_nr, max, events, timeout);
#ifdef DEBUG
fprintf(stdout, "consumed sys-call = %d\n", sys_call_events);
