[GitHub] [activemq-artemis-native] JeffMoyer commented on a change in pull request #7: ARTEMIS-2800 Fixes around Linux Kernel Bug

[GitBox <gi...@apache.org>]

JeffMoyer commented on a change in pull request #7:
URL: https://github.com/apache/activemq-artemis-native/pull/7#discussion_r438761134



##########
File path: src/main/c/org_apache_activemq_artemis_nativo_jlibaio_LibaioContext.c
##########
@@ -129,9 +129,24 @@ static int user_io_getevents(io_context_t aio_ctx, unsigned int max,
                     struct io_event *events)
 {
    long i = 0;
-   unsigned head;
+   unsigned head, tail, avail;
    struct aio_ring *ring = to_aio_ring(aio_ctx);
 
+   // continue until the available values are <= max
+   do {
+       head = ring->head;
+       mem_barrier();
+       tail = ring->tail;
+
+       if (tail >= head)
+           avail = tail - head;
+       else
+           avail = ring->nr - (head - tail);
+
+       if (avail <= max)
+           break;
+    } while (1);

Review comment:
       Nothing should be changing the head pointer, so all you need to do is check for updates to tail.  I think what I sent you was about as simple as you can make that loop.  I also think this code change deserves a comment explaining the kernel bug that it is working around.




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