[Libwebsockets] v1.7.1 high CPU load in LWSS_SHUTDOWN state

Andy Green andy at warmcat.com
Wed Feb 24 14:35:31 CET 2016

On 02/24/2016 09:19 PM, Andrejs Hanins wrote:
> Hi,
>      It's me again about v1.7.1 regressions...
>      This time I get high CPU load due to continuously repeating calls of lws_service_fd from external message loop because of pending POLLOUT. The WSI is in mode=LWSCM_WS_SERVING and state=LWSS_SHUTDOWN. It seems that if lws_callback_on_writable is called in this state then LWS_POLLOUT polling flag is added and it causes immediate trigger of the lws_service_fd which doesn't call lws_handle_POLLOUT_event due to state checks and falls down to handled label without doing anything. But as socket is still writable, lws_service_fd is called again and again, so causing high CPU load.
>      The fix which works for me is ignore lws_callback_on_writable requests is WSI is in LWSS_SHUTDOWN state.
>      Andy, you might have a better fix in mind.

Thanks I pushed a matching fix


The code already took care about defeating POLLOUT when entering 
LWSS_SHUTDOWN but I didn't think about something coming afterwards and 
setting POLLOUT again.


> BR, Andrey
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