IoUring: Correctly refetch completions that were produced because of … (#15480)

normanmaurer · web-flow · commit a9234c32c6ea · 2025-07-13T09:20:40.000+02:00
…inline submissions

Motivation:

We should ensure we refetch the tail of the completion queue and compare
it to the current head before stop processing because a completion might
trigger a submission and so produce more completions.

Modifications:

Refetch tail one more time before exit while loop

Result:

Process completions that were caused by an inline submission without
delay
diff --git a/transport-classes-io_uring/src/main/java/io/netty/channel/uring/CompletionQueue.java b/transport-classes-io_uring/src/main/java/io/netty/channel/uring/CompletionQueue.java
@@ -112,6 +112,12 @@ int process(CompletionCallback callback) {
                     // Stop processing. as the callback can not handle any more completions for now,
                     break;
                 }
+                if (ringHead == tail) {
+                    // Let's fetch the tail one more time as it might have changed because a completion might have
+                    // triggered a submission (io_uring_enter). This can happen as we automatically submit once we
+                    // run out of space in the submission queue.
+                    tail = (int) INT_HANDLE.getVolatile(ktail, 0);
+                }
             }
             return i;
         } finally {

Original file line number	Diff line number	Diff line change
`@@ -112,6 +112,12 @@ int process(CompletionCallback callback) {`
`112`	`112`	`// Stop processing. as the callback can not handle any more completions for now,`
`113`	`113`	`break;`
`114`	`114`	`}`
	`115`	`+ if (ringHead == tail) {`
	`116`	`+ // Let's fetch the tail one more time as it might have changed because a completion might have`
	`117`	`+ // triggered a submission (io_uring_enter). This can happen as we automatically submit once we`
	`118`	`+ // run out of space in the submission queue.`
	`119`	`+ tail = (int) INT_HANDLE.getVolatile(ktail, 0);`
	`120`	`+ }`
`115`	`121`	`}`
`116`	`122`	`return i;`
`117`	`123`	`} finally {`