Re: [linux-audio-dev] Re: Plug-in API progress?

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Subject: Re: [linux-audio-dev] Re: Plug-in API progress?
From: Juhana Sadeharju (kouhia_AT_nic.funet.fi)
Date: ke syys   22 1999 - 12:04:04 EDT


>From: Paul Barton-Davis <pbd_AT_Op.Net>
>
>Just to float an idea: instead of having the GUI run by anything
>related to the engine, put the parameters in shared memory (*).

In my list too. I actully made the playline position transfer via shared
memory in my improved XWave2. There were some problems... it was like
the shared memory would have some delay before showing in another process.
I printed the content of the shared memory play position and it was
 -1 for a long time even the engine updated the position (I heard the audio).
Then when the value was finally available (after 1 to 2 seconds) in GUI
process, the value was jumped to the current position (I never saw the
earlier positions). Perhaps Linux did something weird paging stuff, who
knows?

The code is available at "http://www.funet.fi/~kouhia/waves". Look at
files audio.c (play file stuff) and... and graphics.c (the play button
stuff). I'm not responsible to the complete mess in those files. The code
is very messy and a reason why I started to write my own editor and
not to continue improving the XWave. (My wave editor is not yet available
even I'm using it already --- I need to complete my major audio engine first.)

>manipulation and possibly display of the parameters and other data,
>accessed via shared memory. Benno will love this idea, I'm sure :)

Me too! If GUI peaks the signal level (say) from one memory address, then
there is no buffers or event queues which could freeze the system or cause
delay (of the length of buffer) if GUI freezes for a moment.
Ok, the engine would not freeze at all (if message queues are used for
events, the engine should use nonblocking mode).

Yours,

Juhana


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