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

From: josh
Subject: Re: [fluid-dev] Qsynth broken with FluidSynth 1.1.0
Date: Sat, 07 Nov 2009 01:44:31 -0800
User-agent: Internet Messaging Program (IMP) H3 (4.1.6)

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?


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