Re: [fluid-dev] Qsynth broken with FluidSynth 1.1.0

[josh]

Hello Rui,

I notice that QSynth makes use of fluid_synth_get_channel_preset().   
There have been a number of thread safety issues with FluidSynth, many  
of which have been fixed in 1.1.0.  The issue with that particular  
function, is that presets are allocated when they are assigned to a  
channel and freed when another preset is assigned (a program change  
for example).  This means that currently there are no guarantees that  
the preset returned by fluid_synth_get_channel_preset() will be valid,  
in a multi-thread environment.

I'd like to resolve this issue.  The ideal solution would be to add  
reference counting to presets, but this would require an additional  
API function (fluid_synth_ref_channel_preset() and  
fluid_preset_unref() for example).  Another option would be to add a  
function to query the current preset info, without having to retrieve  
the preset, something like:
fluid_synth_channel_preset_info (synth, chan, &name, &bank, &program);

Trying to get fluid_synth_get_channel_preset() to be thread safe,  
isn't so straightforward though, since there is no way for FluidSynth  
to know how long the calling application will access the preset.  Its  
documented as a "low level access" function, so I was considering just  
making it a function restricted to synthesis context (from a note-on  
method or in the audio driver) and providing other methods of safely  
retrieving the preset info.

By the way, this issue is nothing new.  Older versions of FluidSynth  
could potentially crash QSynth if a program change occurred at the  
right moment.

Any ideas or preferences?

Josh