Re: runsv spinning 100% CPU (was Re: runsv and EAGAIN)

[Gerrit Pape <pape@smarden.org>]

Charlie Brady <charlieb-supervision <at> budge.apana.org.au> writes:
> I've finally found time to look at this issue again, and have found a way 
> to replicate the issue at will.
> 
> To replicate, create a service directory containing an empty file 
> supervise/control in place of the fifo. Create a symlink so that runsvdir 
> spawns a new runsv process. runsv will then behave as shown in the strace 
> plus commentary shown below.
> 
> The unexpected behaviour comes from a combination of two factors - 
> supervise/control is a file and not a fifo, and linux poll() sets POLLIN 
> for a regular file at EOF:
> 
> http://www.greenend.org.uk/rjk/2001/06/poll.html

Yes, I see.

> IMO this is an error condition which runsv should handle more gracefully. 
> The question is - how should the error be handled or corrected? One way 
> would be for runsv to replace any existing supervise/control at startup 
> unless it is a fifo.

Another option would be to have runsv print out an error message like
'supervise/control exists but is not a fifo.' and exit with 111.  This
may be better than forcefully removing a file.

Regards, Gerrit.