[Libwebsockets] libwebsocket message loop thread take 100% of the CPU

Andy Green andy at warmcat.com
Tue Aug 25 07:33:01 CEST 2020

On 8/24/20 4:58 PM, Nagendra Kumar Goel (नगेन्द्र गोयल) wrote:
> What I have specifically seen is that we have a number of worker threads 
> that handle incoming web requests (on the LWS based server) and the main 
> thread has the message processing. The main thread would normally 
> consume 0-1% CPU. However very occasionally (let's say after 10 days of 
> uptime) It would start consuming 100% CPU. Then we have to restart the 
> program to get it back to 0% CPU  usage. I have not yet identified the 
> source of this problem. Interestingly only one binary displays this 
> behavior, and attaching a gdb to the process and pausing it takes me to 
> a join() statement.

Like pthread_join()?  Lws only has one of those in threadpool, which is 
off by default.  If you have other threads active, you'll need to switch 
the gdb thread context to the other threads (info threads, t 2 or 
whatever) and see what they are doing.  pthread_join() is just one 
thread waiting for another to exit, it does not spin.

On Linux you can also come at spinning with perf top, to get a breakdown 
of where the code is spending its time.


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