This avoids use-after-free when handle_start() is called following
handle_stop() during the lifetime of the MetaProfiler. This happens
on repeated profiling sessions using Sysprof.
Fixes: e16d68372 ("profiler: Add API to register profiler threads")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3076>
Otherwise the profiling backend (cogl-trace.c) doesn't actually stop,
and will complain if we try to start it up again.
Fixes: ab39eaf131 ("cogl/trace: Make global start/stop more explicit")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3068>
Don't try to handle things by threads enabling/disabling the main trace
context on-demand, just have a clear start/stop API. For the D-Bus API,
it becomes more straight forward, and for the persistent variant too, as
it avoids having to pass garbage input when it's known that arguments
will be discarded.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2998>
Persistent profiling was started via an env var, but that's rather hard
to discover and remember without grepping; change to use a command line
argument.
The profiler is started early, even during (though late in)
configuration, but configuration should ideally be instant and pointless
to configure.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2998>
It's not really a backend thing, and we'll want to profile e.g. loading
the backend too, so create it very early and destroy it very late and
let MetaContextMain own it.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2678>
