Hi Jérémy,
On Tue, 15 Dec 2009, Jérémy Zurcher wrote:
- don't use all these static methods, or go all static
I don't follow. What do you mean?
- singleton pattern is used amongst other to not
explicitly instanciate and destroy objects, so do so
Some comments on this:
+ The explicit instantiation is required to make
sure that the classes initialize in the correct
order. We kept getting bugs because of a
tangled web of dependencies between various
singletons like Logger, Hydrogen, AudioEngine,
Preferences, Sampler, Playlist, etc.
+ They have to be instantiated /somewhere/. If
the constructor is done at the global scope,
we have no control of the order in which they
are created.
+ The singleton pattern is abused in Hydrogen.
With the exception of Logger (and /maybe/
Preferences), there is no reason for these
classes to be singleton. They amount to
being global variables.
+ Since they're just global variables, why not
make them global variables instead of
singletons?[1]
+ For Composite/Tritium, I have UN-singleton-ed
almost all the classes (as of yesterday):
http://gitorious.org/composite/composite/commit/cafcb6416220b33d192a506275f3ab793c437a58
(Note that Tritium::Engine used to be
H2Core::Hydrogen.) The GUI uses a global
variable for the audio engine.
I also would like to propose to remove the thread from Logger class.
IMO this thread is nothing but resources consuming when things are running well.
And not really usefull when everything goes bad.
While processing audio, there must NOT be any IO, dynamic
memory allocation, or anything that "could wait a long time"
(like a mutex).[2] However, we wish to be able to have some
manner of logging from within the audio parts of Hydrogen.
Therefore, a queue was set up to pass the messages to the
Logger (which can be done in real-ish time[3]). The Logger
has its own thread where it can output the messages at its
leisure.
If you remove the logger thread, you will need some other
thread (GUI?) to do its work... because it must not happen
in the audio parts of the application.
Peace,
Gabriel
[1] See: Hyslop and Sutter, "Once is Not Enough", Dr. Dobb's
Journal March 1, 2003 (http://www.ddj.com/cpp/184401625)
[2] See:
http://jackaudio.org/files/docs/html/group__ClientCallbacks.html#ga62351a5803421b6c21b9ffb9124801ef
[3] QString's constructor and assignment operators
are not realtime safe... so they technically should
not be used in the audio sections either. But,
they remain because the benefits outweight the risks.------------------------------------------------------------------------------
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