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Events: improved error event handling for UDP sockets.
Normally, the epoll module calls the read and write handlers depending
on whether EPOLLIN and EPOLLOUT are reported by epoll_wait(). No error
processing is done in the module, the handlers are expected to get an
error when doing I/O.
If an error event is reported without EPOLLIN and EPOLLOUT, the module
set both EPOLLIN and EPOLLOUT to ensure the error event is handled at
least in one active handler.
This works well unless the error is delivered along with only one of
EPOLLIN or EPOLLOUT, and the corresponding handler does not do any I/O.
For example, it happened when getting EPOLLERR|EPOLLOUT from
epoll_wait() upon receiving "ICMP port unreachable" while proxying UDP.
As the write handler had nothing to send it was not able to detect and
log an error, and did not switch to the next upstream.
The fix is to unconditionally set EPOLLIN and EPOLLOUT in case of an
error event. In the aforementioned case, this causes the read handler
to be called which does recv() and detects an error.
In addition to the epoll module, analogous changes were made in
devpoll/eventport/poll.
| author | Dmitry Volyntsev <xeioex@nginx.com> |
|---|---|
| date | Mon, 21 Nov 2016 16:03:42 +0300 |
| parents | b5ba6f22a0fc |
| children | 1cd63ae46243 |
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<!DOCTYPE html> <html> <head> <title>Error</title> <style> body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; } </style> </head> <body> <h1>An error occurred.</h1> <p>Sorry, the page you are looking for is currently unavailable.<br/> Please try again later.</p> <p>If you are the system administrator of this resource then you should check the <a href="http://nginx.org/r/error_log">error log</a> for details.</p> <p><em>Faithfully yours, nginx.</em></p> </body> </html>