7389a50835
Under high load, a queue synchonization issue may occur, starting from the steady state when an app queue message is dequeued immediately after it has been enqueued. In this state, the router always puts the first message in the queue and is forced to notify the app about a new message in an empty queue using a socket pair. On the other hand, the application dequeues and processes the message without reading the notification from the socket, so the socket buffer overflows with notifications. The issue was reproduced during Unit load tests. After a socket buffer overflow, the router is unable to notify the app about a new first message. When another message is enqueued, a notification is not required, so the queue grows without being read by the app. As a result, request processing stops. This patch changes the notification algorithm by counting the notifications in the pipe instead of getting the number of messages in the queue.
NGINX Unit ---------- The documentation and binary packages are available online: http://unit.nginx.org The source code is provided under the terms of Apache License 2.0: http://hg.nginx.org/unit Please ask questions, report issues, and send patches to the mailing list: unit@nginx.org (http://mailman.nginx.org/mailman/listinfo/unit) or via Github: https://github.com/nginx/unit -- NGINX, Inc. http://nginx.com