[Libwebsockets] libwebsockets loses an event in the poll loop if another FD is closed during that iteration of the poll loop

Bruce Perens bruce at perens.com
Sat May 30 22:14:20 CEST 2015

Libwebsockets can lose an event in a poll loop, if another of the FDs in
the poll FD array is closed during that iteration of the poll loop.

At the end of* libsocket_service_fd()*,
*libwebsocket_close_and_free_session()* causes a callback to the
application with *LWS_CALLBACK_DEL_POLL_FD*. After that, it sets
= 0;*
But the application has changed the poll fd array in response to
*LWS_CALLBACK_DEL_POLL_FD*, and *pollfd* now points to different data than
it previously did. Thus, *revents* is zeroed for the wrong FD.

The symptom of this is that poll() returns a positive integer, and the
number of FDs with revents set is less than the value poll() returned.


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