OpenSim.exe causes cpu spike (Re: supervise causes cpu spike)

[Charlie Brady <charlieb-supervision@budge.apana.org.au>]

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On Sun, 14 Dec 2008, Count László de Almásy wrote:

> I'm hoping someone can help me diagnose why supervising my OpenSim
> process causes it to go up to 100% cpu, while when not supervised, I
> have no such problems. This is on Debian/Linux amd64, with djb's
> latest stock daemontools.
>
> Here's my run script:
>
> ======
> bee:/~# cat /service/opensim/run
> #!/bin/sh
> ulimit -s 262144
> cd /home/opensim/opensim/bin
> exec setuidgid opensim mono OpenSim.exe
> ======

Try:

exec setuidgid opensim mono OpenSim.exe </dev/null

or

exec </dev/null
exec setuidgid opensim mono OpenSim.exe

> stopping/restarting with svc works as expected. it's just, the cpu
> goes right up to 100% with the supervised mono process. running strace
> on the process shows what's happening:
>
> read(0, ""..., 1024)                    = 0
> read(0, ""..., 1024)                    = 0

> [...]
>
> over and over. it's like something is sending the process an empty
> character repeatedly.

No, it's that the process is repeatedly reading standard input in 
non-blocking mode, without first checking that there are any bytes to 
read.

That's a bug in OpenSim.exe (or in mono).

If it is a supervised daemon process, why is it reading standard input?