[Development] QtCS 2017 logging/tracing session notes
thiago.macieira at intel.com
Tue Oct 10 16:28:13 CEST 2017
On Tuesday, 10 October 2017 15:12:52 CEST Christian Gagneraud wrote:
> On 10 October 2017 at 22:48, Thiago Macieira <thiago.macieira at intel.com>
> > do not change qdebug but provide structured tracing as a new facility
> Any chance this can be made lock-free from a caller point of view?
No, we cannot provide a lock-free solution. There's a lot of global state that
needs to be queried so I don't think there's a solution that won't involve a
I'm talking about the implementation. User code should never need to use
> (PS: I don't even know if qDebug streaming is lock-free and i'm
> interested to know the answer:))
It's not. There are mutexes inside.
> A lock-free callee site has the advantage of not influencing (much)
> multi-threading issues. Observing is disturbing as they say.
Which is why it's not going to be lock-free. Even printf has a lock.
> Could this "Structured logging" be it?
> I have as well investigated LTTng, but didn't like their userspace
> boiler plate. In the past, I used LTT in kernel mode and it was very
> simple (LTT was originally made for the Linux Kernel). My (personal)
> conclusion is: if in userspace, better implement your own solution.
Not sure. I looked at the proposed LTTng support for Qt and though it looks
interesting but didn't like the boilerplate either.
> Looking quickly at the code review, I can see that a very few qtbase
> source files have been patched, and a new tool has been added.
That's just proof of concept. The idea was to work on more tracepoints and
more types after the base functionality got merged.
> Could this "Structured logging" provide something along the lines of
> event handler and event dispatcher profiling/tracing?
Possibly, I'm not sure. We concluded during the session we needed more
Thiago Macieira - thiago.macieira (AT) intel.com
Software Architect - Intel Open Source Technology Center
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