[Spice-devel] [PATCH 00/17] WIP: Refactor the streaming agent towards a more standard C++ style

Tue Feb 20 14:36:29 UTC 2018

On Tue, 2018-02-20 at 15:22 +0100, Christophe de Dinechin wrote:
> > On 19 Feb 2018, at 18:29, Lukáš Hrázký <lhrazky at redhat.com> wrote:
> > 
> > On Fri, 2018-02-16 at 17:15 +0100, Christophe de Dinechin wrote:
> > > From: Christophe de Dinechin <dinechin at redhat.com>
> > > 
> > > The streaming agent started as C code. This series converts
> > > the style to something that is more usual for C++, notably:
> > > 
> > > - Adds encapsulation and RAII for resources such as the stream
> > > - Splits functionality into several classes with clear roles
> > > - Puts message formatting and writing in a reused based class
> > > - Isolate what's specific to each message in three derived classes
> > > - Isolate X11-specific code in separate classes, one for cursor messages,
> > >  one for the thread polling the data.
> > > 
> > > Reasons for marking this WIP:
> > > 
> > > 1. This series is, unfortunately, not correctly tested, because on my
> > >   machine, I currently have a black screen with the 'master' streaming
> > >   agent, server, protocol, common, plugin and spicy. Fallback to MJPEG
> > >   leads to a large repetition of messages like:
> > > 
> > >   (spicy:4217): GSpice-CRITICAL **: need more input data
> > > 
> > >   What I have tested using the -d option is that the syslog output
> > >   from the agent looks similar (size of data captured, etc) relative
> > >   to master both for the MJPEG plugin and with fallback. But without
> > >   a picture, I am still concerned about the lack of testing.
> > 
> > Christophe already knows, but in case anyone will benefit from this,
> > it's the incomplete frame bug, fix should be on the ML here:
> > 
> > [Spice-devel] [PATCH spice-server 8/8] stream-channel: Send the full
> > frame in a single message
> > 
> > Christophe, I've tested your patches, it's streaming, but the cursor
> > disappears after a while, so something's not entirely right.
> 
> So there is probably an issue with the cursor message… I will look into it.

See my reply to 12/17 of the series, should probably be the issue.

> What guest type (e.g. f25, rhel…)? I’ve not seen that. I’ll try again and see if I can reproduce.

f27, should not be related.

> > 
> > > 2. The classes were isolated, but not moved in separate headers. This
> > >   is intentional. I prefer to make sure that the changes on the code
> > >   are agreed on before we move the individual classes to their own
> > >   headers. It thinks it will also faclitate history browsing
> > 
> > I'd like to point out the classes are not entirely isolated, there is
> > still the static bool streaming_requested (besides the necessary
> > quit_requested, although I have an idea for that), which ties together
> > the ConcreteAgent::CaptureLoop and Stream::read_command_from_device.
> 
> Interesting. That will force me to re-review the whole thing, because I definitely remember moving streaming_requested within the Stream class, but I don’t see that anymore. Unless I ran into some issue and decided to postpone that?

Must've gotten lost... But the solution to put client_codecs and
supposedly the streaming_requested is honestly ugly :) and seems like
you started taking shortcuts :) I was actually working on that part
myself, so it turned out ok as I have some rough solution, which I'll
need to incorporate with your design, if I can manage that :)

> > 
> > I have an unfinished patch for this, which will need heavy rebasing. In
> > case you are/will be looking into it, Christophe, let me know.
> 
> My reading is that you have a patch for the coupled case (quit). Is it OK if I add one for streaming_requested to the next spin, or do you plan to do that?

I don't have the patch yet, just an idea for the quit. As for
streaming_requested, see above. I'd like to do that, on top of your
patches, once the dust settles a bit...

> > 
> > Lukas
> > 
> > > 3. This series compiles without warnings both with GCC in C++11 mode
> > >   and by clang in gnu++11 mode. However, Frediano pointed out that it
> > >   uses a designated intiializer syntax that is presently a GNU
> > >   extension (the C99 designated initializer syntax). We may consider
> > >   it a problem or not. If it's a problem, it's sufficient to remove
> > >   the designators, but I think they add to readability.
> > > 
> > > 4. Our current configure.ac requires a warning if all initializers are
> > >   not present. Since padding was made explicit in the protocol, this
> > >   requires the code to initialize padding fields, which I don't like.
> > > 
> > > 5. The series integrates off-topic patches sent in a separate series, but
> > >   which are necessary to successfully build with both clang and gcc.
> > > 
> > > This series can also be browsed at
> > > https://gitlab.com/c3d/spice-streaming-agent/merge_requests/1/commits
> > > 
> > > Christophe de Dinechin (17):
> > >  Add missing <string> header
> > >  log_binary is really a boolean
> > >  Eliminate signed/unsigned warning
> > >  Do not create std::string for constants
> > >  Use RAII to cleanup stream in case of exception or return
> > >  Replace inefficient C-style initialization with C++-style
> > >  Get rid of C-style memset initializations, use C++ style aggregates
> > >  Use C++ style for cursor message initialization instead of C style
> > >  Reorder headers according to style guide
> > >  Since we use a namespace, simplify name of local classes
> > >  Move read, write and locking into the 'Stream' class
> > >  Convert message writing from C style to C++ style
> > >  Add more meaningful syslog reporting
> > >  Create a class encapsulating the X11 display cursor capture
> > >  Create FrameLog class to abstract logging of frames
> > >  Remove client_codecs global variable, moved inside the 'Stream' class
> > >  Move the capture loop in the ConcreteAgent, get rid of global agent
> > >    variable
> > > 
> > > src/concrete-agent.cpp        |   1 +
> > > src/concrete-agent.hpp        |   4 +
> > > src/mjpeg-fallback.cpp        |   2 +-
> > > src/spice-streaming-agent.cpp | 521 +++++++++++++++++++++++++-----------------
> > > 4 files changed, 311 insertions(+), 217 deletions(-)
> 
> 