[Xenomai-help] syslog safe?

[Xenomai-help] syslog safe?

[Kent Borg]

Is syslog() safe to call from real time userland code?  (If not, what
is the right way to do such output?)


Thanks,

-kb

Re: [Xenomai-help] syslog safe?

[Philippe Gerum]

Kent Borg wrote:
> Is syslog() safe to call from real time userland code?  (If not, what
> is the right way to do such output?)

No problem using it, but it will trigger an automatic switch to 
secondary mode in order to issue the right Linux syscalls. The thread 
will switch back to primary automatically again as soon as a (usually 
blocking) Xenomai syscall is issued.

-- 

Philippe.

Re: [Xenomai-help] syslog safe?

[Kent Borg]

On Tue, Apr 25, 2006 at 07:52:48PM +0200, Philippe Gerum wrote:
> No problem using it, but it will trigger an automatic switch to 
> secondary mode in order to issue the right Linux syscalls. The thread 
> will switch back to primary automatically again as soon as a (usually 
> blocking) Xenomai syscall is issued.

And, looking at strace output, it appears that is a syslog() is too
low a priority to be logged it doesn't make a system call and so will
not drop us out of realtime.


Thanks,

-kb

Re: [Xenomai-help] syslog safe?

[Philippe Gerum]

Kent Borg wrote:
> On Tue, Apr 25, 2006 at 07:52:48PM +0200, Philippe Gerum wrote:
> 
>>No problem using it, but it will trigger an automatic switch to 
>>secondary mode in order to issue the right Linux syscalls. The thread 
>>will switch back to primary automatically again as soon as a (usually 
>>blocking) Xenomai syscall is issued.
> 
> 
> And, looking at strace output, it appears that is a syslog() is too
> low a priority to be logged it doesn't make a system call and so will
> not drop us out of realtime.
> 
> 

Do not trust strace there, it heavily relies on other glibc services, 
like buffered I/O, which might issue syscalls under various conditions. 
For instance, internal mutex locking might cause a syscall to deal with 
any contended request, or malloc called indirectly might ask for 
extending the caller's data segment, and so on. Additionally, some 
syslog flags, like LOG_CONS, do cause file I/O.

-- 

Philippe.