IoUring: Only fire IoUringBufferRingExhaustedEvent if we could not (#15474)

normanmaurer · chrisvest · web-flow · commit ea823dda3539 · 2025-07-12T09:21:04.000+02:00
expand the ring

Motivation:

When we use a buffer ring we usually increase its size up to a maximum
in batches. Because of this it can happen that we see an ENOBUF but
still can increase the number of buffers in the ring, which means we did
not hit the hard limit yet. If this happens we should better NOT fire an
IoUringBufferRingExhaustedEvent as in reality its not exhausted yet but
just not completely filled to the max.

Modifications:

Only fire IoUringBufferRingExhaustedEvent if we real hit the limit of
the number of buffers that we can put in the ring.

Result:

Less confusing event propagation

---------

Co-authored-by: Chris Vest &lt;christianvest_hansen@apple.com&gt;
diff --git a/transport-classes-io_uring/src/main/java/io/netty/channel/uring/AbstractIoUringStreamChannel.java b/transport-classes-io_uring/src/main/java/io/netty/channel/uring/AbstractIoUringStreamChannel.java
@@ -431,13 +431,13 @@ protected void readComplete0(byte op, int res, int flags, short data, int outsta
             try {
                 if (res < 0) {
                     if (res == Native.ERRNO_NOBUFS_NEGATIVE) {
-                        // recv with provider buffer failed, Fire the BufferRingExhaustedEvent to notify users.
-                        // About the failure. If this happens to often the user should most likely increase the
-                        // buffer ring size.
-                        pipeline.fireUserEventTriggered(bufferRing.getExhaustedEvent());
-
                         // try to expand the buffer ring by adding more buffers to it if there is any space left.
-                        bufferRing.expand();
+                        if (!bufferRing.expand()) {
+                            // We couldn't expand the ring anymore so notify the user that we did run out of buffers
+                            // without the ability to expand it.
+                            // If this happens to often the user should most likely increase the buffer ring size.
+                            pipeline.fireUserEventTriggered(bufferRing.getExhaustedEvent());
+                        }
 
                         // Let's trigger a read again without consulting the RecvByteBufAllocator.Handle as
                         // we can't count this as a "real" read operation.
diff --git a/transport-classes-io_uring/src/main/java/io/netty/channel/uring/IoUringBufferRing.java b/transport-classes-io_uring/src/main/java/io/netty/channel/uring/IoUringBufferRing.java
@@ -159,9 +159,12 @@ private void add(int tail, short bid, int offset, ByteBuf byteBuf) {
 
     /**
      * Try to expand by adding more buffers to the ring if there is any space left, this will be done lazy.
+     *
+     * @return {@code true} if we can expand the number of buffers in the ring, {@code false} otherwise.
      */
-    void expand() {
+    boolean expand() {
         needExpand = true;
+        return allocatedBuffers < buffers.length;
     }
 
     private void fill(short startBid, int buffers) {
